ML021710092

Draft Regulatory Guide DG-3021, Site Evaluations and Determination of Design Earthquake Ground Motion for Seismic Design of Independent Spent Fuel Storage Installations and Monitored Retrievable Storage Installations

ML021710092
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Issue date:	07/31/2002
From:	Shah M Office of Nuclear Regulatory Research
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This regulatory guide is being issued in draft form to involve the public in the early stages of the development of a regulatory position in this area. It has not received complete staff review or approval and does not represent an official NRC staff position.

Public comments are being solicited on this draft guide (including any implementation schedule) and its associated regulatory analysis or value/impact statement. Comments should be accompanied by appropriate supporting data. Written comments may be submitted to the Rules and Directives Branch, Office of Administration, U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001. Comments may be submitted electronically or downloaded through the NRCs interactive web site at <WWW.NRC.GOV> through Rulemaking. Copies of comments received may be examined at the NRC Public Document Room, 11555 Rockville Pike, Rockville, MD. Comments will be most helpful if received by October 7, 2002.

Requests for single copies of draft or active regulatory guides (which may be reproduced) or for placement on an automatic distribution list for single copies of future draft guides in specific divisions should be made to the U.S. Nuclear Regulatory Commission, Washington, DC 20555, Attention:

Reproduction and Distribution Services Section, or by fax to (301)415-2289; or by email to DISTRIBUTION@NRC.GOV. Electronic copies of this draft guide are available through NRCs interactive web site (see above), or the NRCs web site <WWW.NRC.GOV> through the Electronic Reading Room under Accession Number ML021710092.

U.S. NUCLEAR REGULATORY COMMISSION July 2002 OFFICE OF NUCLEAR REGULATORY RESEARCH Division 3 DG-3021 DRAFT REGULATORY GUIDE

Contact:

M. Shah (301)415-8537 DRAFT REGULATORY GUIDE DG-3021 SITE EVALUATIONS AND DETERMINATION OF DESIGN EARTHQUAKE GROUND MOTION FOR SEISMIC DESIGN OF INDEPENDENT SPENT FUEL STORAGE INSTALLATIONS AND MONITORED RETRIEVABLE STORAGE INSTALLATIONS A. INTRODUCTION The NRC has recently published proposed amendments to 10 CFR Part 72, Licensing 1

Requirements for the Independent Storage of Spent Nuclear Fuel and High-Level Radioactive Waste, 2

and Reactor-Related Greater Than Class C Waste. The Proposed Section 72.103, Geological and 3

Seismological Characteristics for Applications for Dry Modes of Storage on or after [insert effective date 4

of Final Rule], in paragraph (f)(1), would require that the geological, seismological, and engineering 5

characteristics of a site and its environs be investigated in sufficient scope and detail to permit an 6

adequate evaluation of the proposed site. The investigation must provide sufficient information to 7

support evaluations performed to arrive at estimates of the design earthquake ground motion (DE) and 8

to permit adequate engineering solutions to actual or potential geologic and seismic effects at the 9

proposed site. In the Proposed Section 72.103, paragraph (f)(2) would require that the geologic and 10 seismic siting factors considered for design include a determination of the DE for the site, the potential 11 for surface tectonic and nontectonic deformations, the design bases for seismically induced floods and 12

2 water waves, and other design conditions. In the Proposed Section 72.103, Paragraph (f)(2)(i) 13 would require that uncertainties inherent in estimates of the DE be addressed through an 14 appropriate analysis, such as a probabilistic seismic hazard analysis (PSHA) or suitable 15 sensitivity analyses.

16 This guide is being developed to provide general guidance on procedures acceptable to 17 the NRC staff for (1) conducting a detailed evaluation of site area geology and foundation 18 stability, (2) conducting investigations to identify and characterize uncertainty in seismic sources 19 in the site region important for the PSHA, (3) evaluating and characterizing uncertainty in the 20 parameters of seismic sources, (4) conducting PSHA for the site, and (5) determining the DE to 21 satisfy the requirements of 10 CFR Part 72.

22 This guide contains several appendices that address the objectives stated above.

23 Appendix A contains definitions of pertinent terms. Appendix B describes the rationale used to 24 determine the reference probability for the DE exceedance level that is acceptable to the staff.

25 Appendix C discusses determination of the probabilistic ground motion level and controlling 26 earthquakes and the development of a seismic hazard information base, Appendix D discusses 27 site-specific geological, seismological, and geophysical investigations. Appendix E describes a 28 method to confirm the adequacy of existing seismic sources and source parameters as the basis 29 for determining the DE for a site. Appendix F describes procedures for determination of the DE.

30 This guide applies to the design basis of both dry cask storage Independent 31 Spent Fuel Storage Installations (ISFSIs) and U.S. Department of Energy monitored 32 retrievable storage installations (MRS), because these facilities are similar in design.

33 The reference probability in Regulatory Position 3.4 and Appendix B does not apply to 34 wet storage because applications for this means of storage are not expected, and it is 35 not cost-effective to allocate resources to develop the technical bases for such an 36 expansion of the proposed revision of Part 72.

37 This guide is consistent with Regulatory Guide 1.165 (Ref. 1), but it has been modified to 38 reflect ISFSI and MRS applications, experience in the use of the dry cask storage methodology, 39 and advancements in the state of knowledge in ground motion modeling (for example, see 40 NUREG/CR-6728 (Ref. 2)).

41 Regulatory guides are issued to describe and make available to the public such 42 information as methods acceptable to the NRC staff for implementing specific parts of the NRCs 43 regulations, techniques used by the staff in evaluating specific problems or postulated accidents, 44 and guidance to applicants. Regulatory guides are not substitutes for regulations, and 45 compliance with regulatory guides is not required. Regulatory guides are issued in draft form for 46 public comment to involve the public in the early stages of developing the regulatory positions.

47 Draft regulatory guides have not received complete staff review and do not represent official 48 NRC staff positions.

49 The information collections contained in this draft regulatory guide are covered by the 50 requirements of 10 CFR Part 72, which were approved by the Office of Management and Budget 51 (OMB), approval number 3150-0132. If a means used to impose an information collection does 52 not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a 53 person is not required to respond to, the information collection.

54

3 B. DISCUSSION 55 BACKGROUND 56 A PSHA has been identified in the proposed Section 72.103 as a means to determine the 57 DE for seismic design of an ISFSI or MRS facility. The proposed rule further recognizes that the 58 nature of uncertainty and the appropriate approach to account for it depends on the tectonic 59 environment of the site and on properly characterizing parameters input to the PSHA, such as 60 seismic sources, the recurrence of earthquakes within a seismic source, the maximum 61 magnitude of earthquakes within a seismic source, engineering estimation of earthquake ground 62 motion, and the level of understanding of the tectonics. Therefore, methods other than 63 probabilistic methods such as sensitivity analyses may be adequate to account for uncertainties.

64 Every site and storage facility is unique, and therefore requirements for analysis and 65 investigations vary. It is not possible to provide procedures for addressing all situations. In 66 cases that are not specifically addressed in this guide, prudent and sound engineering judgment 67 should be exercised.

68 PSHA methodology and procedures were developed during the past 20 to 25 years 69 specifically for evaluation of seismic safety of nuclear facilities. Significant experience has been 70 gained by applying this methodology at nuclear facility sites, both reactor and non-reactor sites, 71 throughout the United States. The Western United States (WUS) (west of approximately 104o 72 west longitude) and the Central and Eastern United States (CEUS) (Refs. 3, 4) have 73 fundamentally different tectonic environments and histories of tectonic deformation. Results of 74 the PSHA methodology applications identified the need to vary the fundamental PSHA 75 methodology application depending on the tectonic environment of a site. The experience with 76 these applications also served as the basis for the Senior Seismic Hazard Analysis Committee 77 guidelines for conducting a PSHA for nuclear facilities (Ref. 5).

78 APPROACH 79 The general process to determine the DE at a new ISFSI or MRS site includes:

80 1.

Site-and region-specific geological, seismological, geophysical, and geotechnical 81 investigations, and 82 2.

A PSHA.

83 For ISFSI sites that are co-located with existing nuclear power generating stations, the 84 level of effort will depend on the availability and quality of existing evaluations. In performing this 85 evaluation, the applicant should evaluate whether new data require re-evaluation of previously 86 accepted seismic sources and potential adverse impact on the existing seismic design bases of 87 the nuclear power plant.

88 CENTRAL AND EASTERN UNITED STATES 89 The CEUS is considered to be that part of the United States east of the Rocky Mountain 90 front, or east of longitude 104o west (Refs. 6, 7). To determine the DE in the CEUS, an accepted 91 PSHA methodology with a range of credible alternative input interpretations should be used. For 92 sites in the CEUS, the seismic hazard methods, the data developed, and seismic sources 93 identified by Lawrence Livermore National Laboratory (LLNL) (Refs. 3, 4, 6) and the Electric 94

4 Power Research Institute (EPRI) (Ref. 7) have been reviewed and are acceptable to the staff.

95 The LLNL and EPRI studies developed data bases and scientific interpretations of available 96 information and determined seismic sources and source characterizations for the CEUS (e.g.,

97 earthquake occurrence rates, estimates of maximum magnitude).

98 In the CEUS, characterization of seismic sources is more problematic than in the active 99 plate-margin region because there is generally no clear association between seismicity and 100 known tectonic structures or near-surface geology. In general, the observed geologic structures 101 were generated in response to tectonic forces that no longer exist and have little or no correlation 102 with current tectonic forces. Therefore, it is important to account for this uncertainty by the use of 103 multiple alternative models.

104 The identification of seismic sources and reasonable alternatives in the CEUS considers 105 hypotheses presently advocated for the occurrence of earthquakes in the CEUS (e.g., the 106 reactivation of favorably oriented zones of weakness or the local amplification and release of 107 stresses concentrated around a geologic structure). In tectonically active areas of the CEUS, 108 such as the New Madrid Seismic Zone, where geological, seismological, and geophysical 109 evidence suggest the nature of the sources that generate the earthquakes, it may be more 110 appropriate to evaluate those seismic sources by using procedures similar to those normally 111 applied in the WUS.

112 WESTERN UNITED STATES 113 The WUS is considered to be that part of the United States that lies west of the Rocky 114 Mountain front, or west of approximately 104o west longitude. For the WUS, an information base 115 of earth science data and scientific interpretations of seismic sources and source 116 characterizations (e.g., geometry, seismicity parameters) comparable to the CEUS as 117 documented in the LLNL and EPRI studies (Refs. 3, 4, 6-8) does not exist. For this region, 118 specific interpretations on a site-by-site basis should be applied (Ref. 9, 10).

119 The active plate-margin regions include, for example, coastal California, Oregon, 120 Washington, and Alaska. For the active plate-margin regions, where earthquakes can often be 121 correlated with known tectonic structures, structures should be assessed for their earthquake 122 and surface deformation potential. In these regions, at least three types of sources may exist:

123 (1) faults that are known to be at or near the surface, (2) buried (blind) sources that may often be 124 manifested as folds at the earths surface, and (3) subduction zone sources, such as those in the 125 Pacific Northwest. The nature of surface faults can be evaluated by conventional surface and 126 near-surface investigation techniques to assess orientation, geometry, sense of displacements, 127 length of rupture, quaternary history, etc.

128 Buried (blind) faults are often associated with surficial deformation such as folding, uplift, 129 or subsidence. The surface expression of blind faulting can be detected by mapping the uplifted 130 or down-dropped geomorphological features or stratigraphy, survey leveling, and geodetic 131 methods. The nature of the structure at depth can often be evaluated by deep core borings and 132 geophysical techniques.

133 Continental U.S. subduction zones are located in the Pacific Northwest and Alaska.

134 Seismic sources associated with subduction zones are sources within the overriding plate, on the 135 interface between the subducting and overriding lithospheric plates, and in the interior of the 136 downgoing oceanic slab. The characterization of subduction zone seismic sources includes 137 consideration of the three-dimensional geometry of the subducting plate, rupture segmentation of 138

5 subduction zones, geometry of historical ruptures, constraints on the up-dip and down-dip extent 139 of rupture, and comparisons with other subduction zones worldwide.

140 The Basin and Range region of the WUS, and to a lesser extent the Pacific Northwest 141 and the Central United States, exhibit temporal clustering of earthquakes. Temporal clustering is 142 best exemplified by the rupture histories within the Wasatch fault zone in Utah and the Meers 143 fault in central Oklahoma, where several large late Holocene coseismic faulting events occurred 144 at relatively close intervals (hundreds to thousands of years) that were preceded by long periods 145 of quiescence that lasted thousands to tens of thousands of years. Temporal clustering should 146 be considered in these regions or wherever paleoseismic evidence indicates that it has occurred.

147 C. REGULATORY POSITION 148

1.

GEOLOGICAL, GEOPHYSICAL, SEISMOLOGICAL, AND GEOTECHNICAL 149 INVESTIGATIONS 150 1.1 Comprehensive geological, seismological, geophysical, and geotechnical investigations of 151 the site area and region should be performed. For ISFSIs co-located with existing nuclear power 152 plants, the existing technical information should be used along with all other available information 153 to plan and determine the scope of additional investigations. The investigations described in this 154 regulatory guide are performed primarily to gather data pertinent to the safe design and 155 construction of the ISFSI or MRS. Appropriate geological, seismological, and geophysical 156 investigations are described in Appendix D to this guide. Geotechnical investigations are 157 described in Regulatory Guide 1.132, Site Investigations for Foundations of Nuclear Power 158 Plants (Ref. 11), and NUREG/CR-5738 (Ref. 12). Another important purpose for the site-159 specific investigations is to determine whether there are any new data or interpretations that are 160 not adequately incorporated into the existing PSHA data bases. Appendix E describes a method 161 for evaluating new information derived from the site-specific investigations in the context of the 162 PSHA.

163 Investigations should be performed at four levels, with the degree of detail based on 164 distance from the site, the nature of the Quaternary tectonic regime, the geological complexity of 165 the site and region, the existence of potential seismic sources, the potential for surface 166 deformation, etc. A more detailed discussion of the areas and levels of investigations and the 167 bases for them are presented in Appendix D to this regulatory guide. General guidelines for the 168 levels of investigation are as follows.

169 1.1.1 Regional geological and seismological investigations are not expected to be extensive nor 170 in great detail, but should include literature reviews, the study of maps and remote 171 sensing data, and, if necessary, ground truth reconnaissances conducted within a radius 172 of 320 km (200 miles) of the site to identify seismic sources (seismogenic and capable 173 tectonic sources).

174 1.1.2 Geological, seismological, and geophysical investigations should be carried out within a 175 radius of 40 km (25 miles) in greater detail than the regional investigations to identify and 176 characterize the seismic and surface deformation potential of any capable tectonic 177 sources and the seismic potential of seismogenic sources, or to demonstrate that such 178 structures are not present. Sites with capable tectonic or seismogenic sources within a 179 radius of 40 km (25 miles) may require more extensive geological and seismological 180

6 investigations and analyses (similar in detail to investigations and analysis usually 181 preferred within an 8-km (5-mile) radius).

182 1.1.3 Detailed geologic, seismological, geophysical, and geotechnical investigations should be 183 conducted within a radius of 8 km (5 miles) of the site, as appropriate, to evaluate the 184 potential for tectonic deformation at or near the ground surface and to assess the 185 transmission characteristics of soils and rocks in the site vicinity. Sites in the CEUS 186 where geologically young or recent tectonic activity is not present may be investigated in 187 less detail. Methods for evaluating the seismogenic potential of tectonic structures and 188 geological features developed in Reference 13 should be followed.

189 1.1.4 Very detailed geological, geophysical, and geotechnical engineering investigations should 190 be conducted within the site [radius of approximately 1 km (0.5 miles)] to assess specific 191 soil and rock characteristics as described in Reference 11, updated with NUREG/CR-192 5738 (Ref. 12).

193 1.2 The areas of investigation may be expanded beyond those specified above in regions that 194 include capable tectonic sources, relatively high seismicity, or complex geology, or in regions that 195 have experienced a large, geologically recent earthquake.

196 1.3 Data sufficient to clearly justify all assumptions and conclusions should be presented.

197 Because engineering solutions cannot always be satisfactorily demonstrated for the effects of 198 permanent ground displacement, it is prudent to avoid a site that has a potential for surface or 199 near-surface deformation. Such sites normally will require extensive additional investigations.

200 1.4 For the site and for the area surrounding the site, lithologic, stratigraphic, hydrologic, and 201 structural geologic conditions should be characterized. The investigations should include the 202 measurement of the static and dynamic engineering properties of the materials underlying the 203 site and an evaluation of the physical evidence concerning the behavior during prior earthquakes 204 of the surficial materials and the substrata underlying the site. The properties needed to assess 205 the behavior of the underlying material during earthquakes, including the potential for 206 liquefaction, and the characteristics of the underlying material in transmitting earthquake ground 207 motions to the foundations of the facility (such as seismic wave velocities, density, water content, 208 porosity, elastic moduli, and strength) should be measured.

209

2.

SEISMIC SOURCES SIGNIFICANT TO THE SITE SEISMIC HAZARD 210 2.1 For sites in the CEUS, when the EPRI or LLNL probabilistic seismic hazard analysis 211 methodologies and data bases are used to determine the design earthquake, it still may be 212 necessary to investigate and characterize potential seismic sources that were unknown or 213 uncharacterized and to perform sensitivity analyses to assess their significance to the seismic 214 hazard estimate. The results of the investigation discussed in Regulatory Position 1 should be 215 used, in accordance with Appendix E, to determine whether the LLNL or EPRI seismic sources 216 and their characterization should be updated. The guidance in Regulatory Positions 2.2 and 2.3 217 below and in Appendix D of this guide may be used if additional seismic sources are to be 218 developed as a result of investigations.

219 2.2 When the LLNL or EPRI methods are not used or are not applicable, the guidance in 220 Regulatory Position 2.3 should be used for identification and characterization of seismic sources.

221 The uncertainties in the characterization of seismic sources should be addressed as appropriate.

222 Seismic sources is a general term referring to both seismogenic sources and capable tectonic 223

7 sources. The main distinction between these two types of seismic sources is that a seismogenic 224 source would not cause surface displacement, but a capable tectonic source causes surface or 225 near-surface displacement.

226 Identification and characterization of seismic sources should be based on regional and 227 site geological and geophysical data, historical and instrumental seismicity data, the regional 228 stress field, and geological evidence of prehistoric earthquakes. Investigations to identify seismic 229 sources are described in Appendix D. The bases for the identification of seismic sources should 230 be identified. A general list of characteristics to be evaluated for seismic sources is presented in 231 Appendix D.

232 2.3 As part of the seismic source characterization, the seismic potential for each source 233 should be evaluated. Typically, characterization of the seismic potential consists of four equally 234 important elements:

235

1.

Selection of a model for the spatial distribution of earthquakes in a source.

236

2.

Selection of a model for the temporal distribution of earthquakes in a source.

237

3.

Selection of a model for the relative frequency of earthquakes of various 238 magnitudes, including an estimate for the largest earthquake that could occur in 239 the source under the current tectonic regime.

240

4.

A complete description of the uncertainty.

241 242 For example, in the LLNL study a truncated exponential model was used for the 243 distribution of magnitudes given that an earthquake has occurred in a source. A stationary 244 Poisson process is used to model the spatial and temporal occurrences of earthquakes in a 245 source.

246 For a general discussion of evaluating the earthquake potential and characterizing the 247 uncertainty, refer to Reference 5.

248 2.3.1 For sites in the CEUS, when the LLNL or EPRI method is not used or not 249 applicable (such as in the New Madrid, MO; Charleston, SC; Attica, NY, Seismic Zones), it is 250 necessary to evaluate the seismic potential for each source. The seismic sources and data that 251 have been accepted by the NRC in past licensing decisions may be used, along with the data 252 gathered from the investigations carried out as described in Regulatory Position 1.

253 Generally, the seismic sources for the CEUS are area sources because there is 254 uncertainty about the underlying causes of earthquakes. This uncertainty is due to a lack of 255 active surface faulting, a low rate of seismic activity, or a short historical record. The assessment 256 of earthquake recurrence for CEUS area sources commonly relies heavily on catalogs of 257 observed seismicity. Because these catalogs are incomplete and cover a relatively short period 258 of time, it is difficult to obtain reliable estimates of the rate of activity. Considerable care must be 259 taken to correct for incompleteness and to model the uncertainty in the rate of earthquake 260 recurrence. To completely characterize the seismic potential for a source, it is also necessary to 261 estimate the largest earthquake magnitude that a seismic source is capable of generating under 262 the current tectonic regime. This estimated magnitude defines the upper bound of the 263 earthquake recurrence relationship.

264

8 The assessment of earthquake potential for area sources is particularly difficult because 265 one of the physical constraints most important to the assessment, the dimensions of the fault 266 rupture, is not known. As a result, the primary methods for assessing maximum earthquakes for 267 area sources usually include a consideration of the historical seismicity record, the pattern and 268 rate of seismic activity, the Quaternary (2 million years and younger) characteristics of the 269 source, the current stress regime (and how it aligns with known tectonic structures), paleoseismic 270 data, and analogs to sources in other regions considered tectonically similar to the CEUS.

271 Because of the shortness of the historical catalog and low rate of seismic activity, considerable 272 judgment is needed. It is important to characterize the large uncertainties in the assessment of 273 the earthquake potential.

274 2.3.2 For sites located within the WUS, earthquakes can often be associated with 275 known tectonic structures. For faults, the earthquake potential is related to the characteristics of 276 the estimated future rupture, such as the total rupture area, the length, or the amount of fault 277 displacement. The following empirical relations can be used to estimate the earthquake potential 278 from fault behavior data and also to estimate the amount of displacement that might be expected 279 for a given magnitude. It is prudent to use several of the following different relations to obtain an 280 estimate of the earthquake magnitude.

281 Surface rupture length versus magnitude (Refs. 14-17),

282 Subsurface rupture length versus magnitude (Ref. 18),

283 Rupture area versus magnitude (Ref. 19),

284 Maximum and average displacement versus magnitude (Ref. 18), and 285 Slip rate versus magnitude (Ref. 20).

286 When such correlations as in References 14-20 are used, the earthquake potential is 287 often evaluated as the mean of the distribution. The difficult issue is the evaluation of the 288 appropriate rupture dimension to be used. This is a judgmental process based on geological 289 data for the fault in question and the behavior of other regional fault systems of the same type.

290 In addition to maximum magnitude, the other elements of the recurrence model are 291 generally obtained using catalogs of seismicity, fault slip rate, and other data. In some cases, it 292 may be appropriate to use recurrence models with memory. All the sources of uncertainty must 293 be appropriately modeled. Additionally, the phenomenon of temporal clustering should be 294 considered when there is geological evidence of its past occurrence.

295 2.3.3 For sites near subduction zones, such as in the Pacific Northwest and Alaska, the 296 maximum magnitude must be assessed for subduction zone seismic sources. Worldwide 297 observations indicate that the largest known earthquakes are associated with the plate interface, 298 although intraslab earthquakes may also have large magnitudes. The assessment of plate 299 interface earthquakes can be based on estimates of the expected dimensions of rupture or 300 analogies to other subduction zones worldwide.

301

3.

PROBABILISTIC SEISMIC HAZARD ANALYSIS PROCEDURES 302 A PSHA should be performed for the site as it allows the use of multiple models to 303 estimate the likelihood of earthquake ground motions occurring at a site and systematically takes 304 into account uncertainties that exist in various parameters (such as seismic sources, maximum 305 earthquakes, and ground motion attenuation). Alternative hypotheses are considered in a 306 quantitative fashion in a PSHA. Alternative hypotheses can also be used to evaluate the 307

9 sensitivity of the hazard to the uncertainties in the significant parameters and to identify the 308 relative contribution of each seismic source to the hazard.

309 The following steps describe a procedure that is acceptable to the NRC staff for 310 performing a PSHA.

311 3.1 Perform regional and site geological, seismological, and geophysical investigations in 312 accordance with Regulatory Position 1 and Appendix D.

313 3.2 For CEUS sites, perform an evaluation of LLNL or EPRI seismic sources in accordance 314 with Appendix E to determine whether they are consistent with the site-specific data gathered in 315 Regulatory Position 1 or require updating. The PSHA should only be updated if the new 316 information indicates that the current version significantly underestimates the hazard and there is 317 a strong technical basis that supports such a revision. It may be possible to justify a lower 318 hazard estimate with an exceptionally strong technical basis. However, it is expected that large 319 uncertainties in estimating seismic hazard in the CEUS will continue to exist in the future, and 320 substantial delays in the licensing process will result in trying to justify a lower value with respect 321 to a specific site. For these reasons the NRC staff discourages efforts to justify a lower hazard 322 estimate. In most cases, limited-scope sensitivity studies should be sufficient to demonstrate 323 that the existing data base in the PSHA envelops the findings from site-specific investigations. In 324 general, significant revisions to the LLNL and EPRI data base are to be undertaken only 325 periodically (every 10 years), or when there is an important new finding or occurrence. An overall 326 revision of the data base would also require a reexamination of the acceptability of the reference 327 probability discussed in Appendix B and used in Regulatory Position 4 below. Any significant 328 update should follow the guidance of Reference 5.

329 3.3 For CEUS sites only, perform the LLNL or EPRI PSHA using original or updated sources 330 as determined in Regulatory Position 2. For sites in WUS, perform a site-specific PSHA (Ref. 5).

331 The ground motion estimates should be made for rock conditions in the free-field or by assuming 332 hypothetical rock conditions for a non-rock site to develop the seismic hazard information base 333 discussed in Appendix C.

334 3.4 Using the mean reference probability (5E-4/yr) described in Appendix B, determine the 5 335 percent of critically damped mean spectral ground motion levels for 1 Hz (Sa,1) and 10 Hz (Sa,10) 336 (Ref. 2). The use of an alternative reference probability will be reviewed and accepted on a 337 case-by-case basis.

338 3.5 Deaggregate the mean probabilistic hazard characterization in accordance with Appendix 339 C to determine the controlling earthquakes (i.e., magnitudes and distances), and document the 340 hazard information base, as described in Appendix C.

341 3.6 As an alternative method, instead of the controlling earthquakes approach described in 342 Appendix C and Regulatory Position 4 below, determine the ground motions at a sufficient 343 number of frequencies significant to the ISFSI or MRS design, and then envelope the ground 344 motions to determine the DE.

345

4.

PROCEDURES FOR DETERMINING THE DESIGN EARTHQUAKE GROUND MOTION 346

10 After completing the PSHA (see Regulatory Position 3) and determining the controlling 347 earthquakes, the following procedures should be used to determine the DE. Appendix F 348 contains an additional discussion of some of the characteristics of the DE.

349 4.1 With the controlling earthquakes determined as described in Regulatory Position 3 and by 350 using the procedures in Revision 3 of Reference 21 (which may include the use of ground motion 351 models not included in the PSHA but that are more appropriate for the source, region, and site 352 under consideration or that represent the latest scientific development), develop 5 percent of 353 critical damping response spectral shapes for the actual or assumed rock conditions. The same 354 controlling earthquakes are also used to derive vertical response spectral shapes.

355 4.2 Use Sa,10 to scale the response spectrum shape corresponding to the controlling 356 earthquake. If there is a controlling earthquake for Sa,1, determine that the Sa,10 scaled response 357 spectrum also envelopes the ground motion spectrum for the controlling earthquake for Sa,1.

358 Otherwise, modify the shape to envelope the low-frequency spectrum or use two spectra in the 359 following steps. For a rock site, go to Regulatory Position 4.4.

360 4.3 For non-rock sites, perform a site-specific soil amplification analysis considering 361 uncertainties in site-specific geotechnical properties and parameters to determine response 362 spectra at the free ground surface in the free-field for the actual site conditions. Procedures 363 described in Appendix D of this guide and Reference 21 can be used to perform soil-amplification 364 analyses.

365 4.4 Compare the smooth DE spectrum or spectra used in design at the free-field with the 366 spectrum or spectra determined in Regulatory Position 2 for rock sites or determined in 367 Regulatory Position 3 for the non-rock sites to assess the adequacy of the DE spectrum or 368 spectra.

369 4.5 To obtain an adequate DE based on the site-specific response spectrum or spectra, 370 develop a smooth spectrum or spectra or use a standard broad band shape that envelopes the 371 spectra of Regulatory Position 2 or 3.

372 D. IMPLEMENTATION 373 The purpose of this section is to provide information to applicants and licensees regarding 374 the NRC staffs plans for using this draft regulatory guide.

375 This draft guide has been released to encourage public participation in its development.

376 Except in those cases in which an applicant or licensee proposes an acceptable alternative 377 method for complying with the specified portions of the NRCs regulations, the methods to be 378 described in the active guide reflecting public comments will be used in the evaluation of 379 applications for new dry cask ISFSI and MRS facilities.

380

1 Copies are available at current rates from the U.S. Government Printing Office, P.O. Box 37082, Washington, DC 20402-9328 (telephone (202)512-1800); or from the National Technical Information Service by writing NTIS at 5285 Port Royal Road, Springfield, VA 22161; (telephone (703)487-4650; <http://www.ntis.gov/ordernow>. Copies are available for inspection or copying for a fee from the NRC Public Document Room at 11555 Rockville Pike, Rockville, MD; the PDRs mailing address is USNRC PDR, Washington, DC 20555; telephone (301)415-4737 or (800)397-4209; fax (301)415-3548; email is PDR@NRC.GOV.

2 Copies are available for inspection or copying for a fee from the NRC Public Document Room at 11555 Rockville Pike (first floor), Rockville, MD; the PDRs mailing address is USNRC PDR, Washington, DC 20555; telephone (301)415-4737 or 1-(800)397-4209; fax (301)415-3548; e-mail <PDR@NRC.GOV>.

11 REFERENCES 381

1.

USNRC, Identification and Characterization of Seismic Sources and Determination of 382 Safe Shutdown Earthquake Ground Motion, Regulatory Guide 1.165, March 1997.3 383

2.

R.K. McGuire, W.J. Silva, and C.J. Constantino, Technical Basis for Revision of 384 Regulatory Guidance on Design Ground Motions: Hazard-and Risk-Consistent Ground 385 Motion Spectra Guidelines, NUREG/CR-6728, October 2001.

386

3.

D.L. Bernreuter et al., "Seismic Hazard Characterization of 69 Nuclear Plant Sites East of 387 the Rocky Mountains," NUREG/CR-5250, Volumes 1-8, 1989.1 388

4.

P. Sobel, "Revised Livermore Seismic Hazard Estimates for Sixty-Nine Nuclear Power 389 Plant Sites East of the Rocky Mountains," NUREG-1488, USNRC, April 1994.1 390

5.

R.J. Budnitz et al., "Recommendations for Probabilistic Seismic Hazard Analysis:

391 Guidance on Uncertainty and Use of Experts," NUREG/CR-6372, Volumes 1 and 2, 392 USNRC, April 1997.1 393

6.

J.B. Savy et al., "Eastern Seismic Hazard Characterization Update," UCRL-ID-115111, 394 Lawrence Livermore National Laboratory, June 1993.2 (Accession number 9310190318 395 in NRC's Public Document Room) 396

7.

Electric Power Research Institute (EPRI), "Probabilistic Seismic Hazard Evaluations at 397 Nuclear Power Plant Sites in the Central and Eastern United States," NP-4726, All 398 Volumes, 1989-1991.

399

8.

Electric Power Research Institute (EPRI), The Earthquakes of Stable Continental 400 Regions, Volume 1: Assessment of Large Earthquake Potential, EPRI TR-102261-V1, 401 1994.

402

9.

Pacific Gas and Electric Company, "Final Report of the Diablo Canyon Long Term 403 Seismic Program; Diablo Canyon Power Plant," Docket Nos. 50-275 and 50-323, 1988.2 404

10.

H. Rood et al., "Safety Evaluation Report Related to the Operation of Diablo Canyon 405 Nuclear Power Plant, Units 1 and 2," NUREG-0675, Supplement No. 34, USNRC, June 406 1991.1 407

3 Requests for single copies of draft or active regulatory guides (which may be reproduced) or for placement on an automatic distribution list for single copies of future draft guides in specific divisions should be made in writing to the U.S. Nuclear Regulatory Commission, Washington, DC 20555, Attention: Reproduction and Distribution Services Section, or by fax to (301)415-2289; email <DISTRIBUTION@NRC.GOV>. Copies are available for inspection or copying for a fee from the NRC Public Document Room at 11555 Rockville Pike (first floor),

Rockville, MD; the PDRs mailing address is USNRC PDR, Washington, DC 20555; telephone (301)415-4737 or 1-(800)397-4209; fax (301)415-3548; e-mail <PDR@NRC.GOV>.

12

11.

USNRC, "Site Investigations for Foundations of Nuclear Power Plants," Regulatory Guide 408 1.132, March 1979. (See also DG-1101, the proposed Revision 2 of Regulatory Guide 409 1.132, February 2001.)3 410

12.

N. Torres et al., Field Investigations for Foundations of Nuclear Power Facilities, 411 NUREG/CR-5738, USNRC, 1999.1 412

13.

K.L. Hanson et al., Techniques for Identifying Faults and Determining Their Origins, 413 NUREG/CR-5503, USNRC, July 1999.1 414

14.

D.B. Slemmons, Faults and Earthquake Magnitude, U.S. Army Corps of Engineers, 415 Waterways Experiment Station, Misc. Papers S-7-1, Report 6, 1997.

416

15.

D.B. Slemmons, Determination of Design Earthquake Magnitudes for Microzonation, 417 Proceedings of the Third International Microzonation Conference, University of 418 Washington, Seattle, Volume 1, pp. 119-130, 1982.

419

16.

M.G. Bonilla, H.A. Villalobos, and R.E. Wallace, Exploratory Trench Across the Pleasant 420 Valley Fault, Nevada, Professional Paper 1274-B, U.S. Geological Survey, pp. B1-B14, 421 1984.2 422

17.

S.G. Wesnousky, Relationship Between Total Affect, Degree of Fault Trace 423 Complexibility, and Earthquake Size on Major Strike-Slip Faults in California, (Abs),

424 Seismological Research Letters, Volume 59, No. 1, p.3, 1988.

425

18.

D.L. Wells and K.J. Coppersmith, New Empirical Relationships Among Magnitude, 426 Rupture Length, Rupture Width, Rupture Area, and Surface Displacement, Bulletin of the 427 Seisomological Society of America, Volume 84, 1994.

428

19.

M. Wyss, Estimating Maximum Expectable Magnitude of Earthquakes from Fault 429 Dimensions, Geology, Volume 7 (7), pp. 336-340, 1979.

430

20.

D.P. Schwartz and K.J. Coppersmith, Seismic Hazards: New Trends in Analysis Using 431 Geologic Data, Active Tectonics, National Academy Press, Washington, DC, pp. 215-432 230, 1986.

433

21.

USNRC, Standard Review Plan for the Review of Safety Analysis Reports for Nuclear 434 Power Plants, NUREG-0800, Section 2.5.2, Revision 3, 1997.3 435 APPENDIX A 436 DEFINITIONS 437

13 Capable Tectonic Source A capable tectonic source is a tectonic structure that can generate 438 both vibratory ground motion and tectonic surface deformation such as faulting or folding at or 439 near the earths surface in the present seismotectonic regime. It is described by at least one of 440 the following characteristics:

441

a.

Presence of surface or near-surface deformation of landforms or geologic 442 deposits of a recurring nature within the last approximately 500,000 years or at 443 least once in the last approximately 50,000 years.

444

b.

A reasonable association with one or more moderate to large earthquakes or 445 sustained earthquake activity, usually accompanied by significant surface 446 deformation.

447

c.

A structural association with a capable tectonic source that has characteristics of 448 either a or b above such that movement on one could be reasonably expected to 449 be accompanied by movement on the other.

450 In some cases, the geological evidence of past activity at or near the ground surface along a 451 potential capable tectonic source may be obscured at a particular site. This might occur, for 452 example, at a site having a deep overburden. For these cases, evidence may exist elsewhere 453 along the structure from which an evaluation of its characteristics in the vicinity of the site can be 454 reasonably based. Such evidence is to be used in determining whether the structure is a 455 capable tectonic source within this definition.

456 Notwithstanding the foregoing paragraphs, the association of a structure with geological 457 structures that are at least pre-Quaternary, such as many of those found in the Central and 458 Eastern regions of the United States, in the absence of conflicting evidence, will demonstrate that 459 the structure is not a capable tectonic source within this definition.

460 Controlling Earthquakes Controlling earthquakes are the earthquakes used to determine 461 spectral shapes or to estimate ground motions at the site. There may be several controlling 462 earthquakes for a site. As a result of the probabilistic seismic hazard analysis (PSHA),

463 controlling earthquakes are characterized as mean magnitudes and distances derived from a 464 deaggregation analysis of the mean estimate of the PSHA.

465 Design Earthquake Ground Motion (DE) The DE is the vibratory ground motion for which 466 certain structures, systems, and components, classified as important to safety, are designed, 467 pursuant to Part 72. The DE for the site is characterized by both horizontal and vertical free-field 468 ground motion response spectra at the free ground surface.

469 Earthquake Recurrence Earthquake recurrence is the frequency of occurrence of 470 earthquakes having various magnitudes. Recurrence relationships or curves are developed for 471 each seismic source, and they reflect the frequency of occurrence (usually expressed on an 472 annual basis) of magnitudes up to the maximum, including measures of uncertainty.

473 Intensity The intensity of an earthquake is a qualitative description of the effects of the 474 earthquake at a particular location, as evidenced by observed effects on humans, on human-built 475 structures, and on the earths surface at a particular location. Commonly used scales to specify 476 intensity are the Rossi-Forel, Mercalli, and Modified Mercalli. The Modified Mercalli Intensity 477 (MMI) scale describes intensities with values ranging from I to XII in the order of severity. MMI of 478

14 I indicates an event that was not felt except by a very few, while MMI of XII indicates total 479 damage of all works of construction, either partially or completely.

480 Magnitude An earthquakes magnitude is a measure of the strength of an earthquake as 481 determined from seismographic observations and is an objective, quantitative measure of the 482 size of an earthquake. The magnitude is expressed in various ways based on the seismograph 483 record, e.g., Richter Local Magnitude, Surface Wave Magnitude, Body Wave Magnitude, and 484 Moment Magnitude. The most commonly used magnitude measurement is the Moment 485 Magnitude, Mw, which is based on the seismic moment computed as the rupture force along the 486 fault multiplied by the average amount of slip, and thus is a direct measure of the energy 487 released during an earthquake event. The Moment Magnitude of an earthquake event (Mw or M) 488 varies from 2.0 and higher values, and since magnitude scales are logarithmic, a unit change in 489 magnitude corresponds to a 32-fold change in the energy released during an earthquake event.

490 Maximum Magnitude The maximum magnitude is the upper bound to recurrence curves.

491 Mean Annual Probability of Exceedance Mean annual probability of exceedance of an 492 earthquake event of a given magnitude or an acceleration level is the probability that the given 493 magnitude or acceleration level may exceed in a year. The mean annual probability of 494 exceedance of an earthquake event is a reciprocal of the return period of the event.

495 Nontectonic Deformation Nontectonic deformation is distortion of surface or near-surface 496 soils or rocks that is not directly attributable to tectonic activity. Such deformation includes 497 features associated with subsidence, karst terrain, glaciation or deglaciation, and growth faulting.

498 Reference Probability - The reference probability of occurrence of an earthquake event is the 499 mean annual probability of exceeding the design earthquake.

500 Response Spectrum A plot of the maximum values of responses (acceleration, velocity, or 501 displacement) of a family of idealized single-degree-of-freedom damped oscillators as a function 502 of its natural frequencies (or periods) to a specified vibratory motion input at their supports.

503 Return Period The return period of an earthquake event is an inverse of the mean annual 504 probability of exceedance of the earthquake event.

505 Safe Shutdown Earthquake (SSE) The SSE is the vibratory ground motion for which certain 506 structures, systems, and components in a nuclear power plant are designed, pursuant to 507 Appendix S to 10 CFR Part 50, to remain functional. The SSE for the site is characterized by 508 both horizontal and vertical free-field ground motion response spectra at the free ground surface.

509 Seismic Potential A model giving a complete description of the future earthquake activity in a 510 seismic source zone. The model includes a relation giving the frequency (rate) of earthquakes of 511 any magnitude, an estimate of the largest earthquake that could occur under the current tectonic 512 regime, and a complete description of the uncertainty. A typical model used for PSHA is the use 513 of a truncated exponential model for the magnitude distribution and a stationary Poisson process 514 for the temporal and spatial occurrence of earthquakes.

515 Seismic Source Seismic source is a general term referring to both seismogenic sources and 516 capable tectonic sources.

517

15 Seismogenic Source A seismogenic source is a portion of the earth that is assumed to have 518 a uniform earthquake potential (same expected maximum earthquake and recurrence 519 frequency), distinct from the seismicity of the surrounding regions. A seismogenic source will 520 generate vibratory ground motion but is assumed not to cause surface displacement.

521 Seismogenic sources cover a wide range of possibilities, from a well-defined tectonic structure to 522 simply a large region of diffuse seismicity (seismotectonic province) thought to be characterized 523 by the same earthquake recurrence model. A seismogenic source is also characterized by its 524 involvement in the current tectonic regime (the Quaternary, or approximately the last 2 million 525 years).

526 Stable Continental Region (SCR) A stable continental region is composed of continental 527 crust, including continental shelves, slopes, and attenuated continental crust, and excludes active 528 plate boundaries and zones of currently active tectonics directly influenced by plate margin 529 processes. It exhibits no significant deformation associated with the major Mesozoic-to-Cenozoic 530 (last 240 million years) orogenic belts. It excludes major zones of Neogene (last 25 million years) 531 rifting, volcanism, or suturing.

532 Stationary Poisson Process A probabilistic model of the occurrence of an event over time 533 (or space) that has the following characteristics: (1) the occurrence of the event in small intervals 534 is constant over time (or space), (2) the occurrence of two (or more) events in a small interval is 535 negligible, and (3) the occurrence of the event in non-overlapping intervals is independent.

536 Tectonic Structure A tectonic structure is a large-scale dislocation or distortion, usually within 537 the earths crust. Its extent may be on the order of tens of meters (yards) to hundreds of 538 kilometers (miles).

539

16 APPENDIX B 540 REFERENCE PROBABILITY FOR THE EXCEEDANCE LEVEL OF THE 541 DESIGN EARTHQUAKE GROUND MOTION 542 B.1 INTRODUCTION 543 This appendix provides a rationale for a reference probability that is acceptable to the 544 NRC staff. The reference probability is used in conjunction with the probabilistic seismic hazard 545 analysis (PSHA) for determining the Design Earthquake Ground Motion (DE) for ISFSI or MRS 546 designs.

547 B.2 QUESTION ON REFERENCE PROBABILITY FOR DESIGN EARTHQUAKE 548 The reference probability is the mean annual probability of exceeding the DE. It is the 549 reciprocal of the return period for the design earthquake.

550 The NRC staff welcomes comments on all aspects of this draft regulatory guide, but is 551 especially interested in receiving comments on the appropriate mean annual probability of 552 exceedance value to be used for the seismic design of an ISFSI or MRS. Please note the 553 following considerations and include a justification for the appropriate mean annual probability of 554 exceedance value.

555 The present mean annual probability of exceedance value for determining the DE for an 556 ISFSI or MRS is approximately 1.0E-04 (i.e., in any one year, the probability is 1 in 10,000, which 557 is the reciprocal of 1.0E-04, that the DE established for the site will be exceeded). This value is 558 based on requirements for nuclear plants. The NRC is considering allowing for the use of a 559 mean annual probability of exceedance value in the range of 5.0E-04 (i.e., in any one year, the 560 probability is 1 in 2,000 that the DE established for the site will be exceeded) to 1.0E-04 for ISFSI 561 or MRS applications. This Draft Regulatory Guide DG-3021, Site Evaluations and Determination 562 of Design Earthquake Ground Motion for Seismic Design of Independent Spent Fuel Storage 563 Installations and Monitored Retrievable Storage Installations, is being developed to provide 564 guidelines that are acceptable to the NRC staff for determining the DE for an ISFSI or MRS. DG-565 3021 proposes to recommend a mean annual probability of exceedance value of 5.0E-04 as an 566 appropriate risk-informed value for the design of a dry storage ISFSI or MRS. However, the NRC 567 staff is undertaking further analysis to support a specific value. An ISFSI or MRS license 568 applicant would have to demonstrate that the use of a higher probability of exceedance value 569 would not impose any undue radiological risk to public health and safety. In view of this 570 discussion, the NRC staff is requesting comments on the appropriate mean annual probability of 571 exceedance value to be used for the seismic design of an ISFSI or MRS and a justification for 572 this probability.

573 B.3 RATIONALE FOR THE REFERENCE PROBABILITY 574 The following describes the rationale for determining the reference probability for use in 575 the PSHA for a dry cask storage system (DCSS) during a seismic event. The mean reference 576 probability of exceedance of 5.0E-4/yr for a seismic event is considered appropriate for the 577 design of a DCSS. The use of a higher reference probability will be reviewed and accepted on a 578 case-by-case basis.

579 B.3.1 Part 72 Approach 580

17 Part 72 regulations classify the structures, systems, and components (SSC) in an ISFSI 581 or MRS facility based on their importance to safety. SSCs are classified as important to safety if 582 they have the function of protecting public health and safety from undue risk and preventing 583 damage to the spent fuel during handling and storage. These SSCs are evaluated for a single 584 level of DE as an accident condition event only (section 72.106). For normal operations and 585 anticipated occurrences (section 72.104), earthquake events are not included.

586 The DCSSs for ISFSIs or MRSs are typically self-contained massive concrete or steel 587 structures, weighing approximately 40 to 100 tons when fully loaded. There are very few, if any, 588 moving parts. They are set on a concrete support pad. Several limitations have been set on the 589 maximum height to which the casks can be lifted, based on the drop accident analysis. There is 590 a minimum center-to-center spacing requirement for casks stored in an array on a common 591 support pad. The most conservative estimates of structural thresholds of seismic inertia 592 deceleration from a drop accident event, before the confinement is breached so as to exceed the 593 permissible radiation levels, is in the range of 30 g to 40 g.

594 B.3.2 Reference Probability 595 The present DE is based on the requirements contained in 10 CFR Part 100 for nuclear 596 power plants. In the Statement of Considerations accompanying the initial Part 72 rulemaking, 597 the NRC recognized that the design peak horizontal acceleration for structures, systems, and 598 components (SSCs) need not be as high as for a nuclear power reactor and should be 599 determined on a case-by-case basis until more experience is gained with licensing of these 600 types of units (45 FR 74697; November 12, 1980). With over 10 years of experience in licensing 601 dry cask storage and with analyses that demonstrate robust behavior of dry cask storage 602 systems (DCSSs) in accident scenarios (10 specific licenses have been issued and 9 locations 603 use the general license provisions), the NRC now has a reasonable basis to consider lower and 604 more appropriate DE parameters for a dry cask ISFSI or MRS. Therefore, the NRC proposes to 605 reduce the DE for new ISFSI or MRS license applicants to be commensurate with the lower risk 606 associated with these facilities. Factors that result in lower radiological risk at an ISFSI or MRS 607 compared to a nuclear power plant include the following:

608 609

In comparison with a nuclear power plant, an operating ISFSI or MRS is a relatively 610 simple facility in which the primary activities are waste receipt, handling, and storage. An 611 ISFSI or MRS does not have the variety and complexity of active systems necessary to 612 support an operating nuclear power plant. After the spent fuel is in place, an ISFSI or 613 MRS is essentially a static operation.

614

During normal operations, the conditions required for the release and dispersal of 615 significant quantities of radioactive materials are not present. There are no high 616 temperatures or pressures present during normal operations or under design basis 617 accident conditions to cause the release and dispersal of radioactive materials. This is 618 primarily due to the low heat-generation rate of spent fuel that has undergone more than 619 1 year of decay before storage in an ISFSI or MRS, and to the low inventory of volatile 620 radioactive materials readily available for release to the environment.

621

The long-lived nuclides present in spent fuel are tightly bound in the fuel materials and 622 are not readily dispersible. Short-lived volatile nuclides, such as I-131, are no longer 623 present in aged spent fuel. Furthermore, even if the short-lived nuclides were present 624 during a fuel assembly rupture, the canister surrounding the fuel assemblies would 625 confine these nuclides. Therefore, the Commission believes that the seismically induced 626

18 radiological risk associated with an ISFSI or MRS is significantly less than the risk 627 associated with a nuclear power plant. Also, it is NRC policy to use risk-informed 628 regulation as appropriate.

629

The critical element for protection against radiation release is the sealed cask containing 630 the spent fuel assemblies. The standards in Part 72 in Subparts E, Siting Evaluation 631 Factors, and F, General Design Criteria, ensure that the dry cask storage designs are 632 very rugged and robust. The casks must maintain structural integrity during a variety of 633 postulated non-seismic events, including cask drops, tip-overs, and wind-driven missile 634 impacts. These non-seismic events challenge cask integrity significantly more than 635 seismic events. Therefore, the casks are expected to have substantial design margins to 636 withstand forces from a seismic event greater than the design earthquake.

637

During a seismic event at an ISFSI or MRS, a cask may slide if lateral seismic forces are 638 greater than the frictional resistance between the cask and the concrete pad. The sliding 639 and resulting displacements are computed by the applicant to demonstrate that the 640 casks, which are spaced to satisfy the thermal criteria in Subpart F of Part 72, are 641 precluded from impacting other adjacent casks. Furthermore, the NRC staff guidance in 642 reviewing cask designs is to show that public health and safety is maintained during a 643 postulated DE. This can be demonstrated by showing that either casks are designed to 644 prevent sliding or tip over during a seismic event, or the consequences of the calculated 645 cask movements are acceptable. Even if the casks slide or tip over and then impact 646 other casks or the pad during a seismic event significantly greater than the proposed DE, 647 there are adequate design margins to ensure that the casks maintain their structural 648 integrity.

649

The combined probability of the occurrence of a seismic event and operational failure that 650 leads to a radiological release is much smaller than the individual probabilities of either of 651 these events. This is because the handling building and crane are used for only a fraction 652 of the licensed period of an ISFSI or MRS and for only a few casks at a time.

653 Additionally, dry cask ISFSIs are expected to handle only sealed casks and not individual 654 fuel assemblies. Therefore, the potential risk of a release of radioactivity caused by 655 failure of the cask handling or crane during a seismic event is small.

656 Additional factors for reducing the DE for new ISFSI or MRS license applicants include:

657

Because the DE is a smooth broad-band spectrum that envelops the controlling 658 earthquake responses, the vibratory ground motion specified is conservative.

659

The crane used for lifting the casks in the building is designed using the same industry 660 codes as for a nuclear power plant, and has a safety factor of 5 or greater for lifted loads 661 using the ultimate strength of the materials. Therefore, the crane would perform 662 satisfactorily during an earthquake much larger than the design earthquake.

663

1 U.S. Department of Energy, Natural Phenomena Hazards Design Evaluation Criteria for Department of Energy Facilities, DOE-STD-1020-2002, January 2002. Copies are available at current rates from the U.S. Government Printing Office, P.O. Box 37082, Washington, DC 20402-9328 (telephone (202)512-1800); or from the National Technical Information Service by writing NTIS at 5285 Port Royal Road, Springfield, VA 22161; (telephone (703)487-4650; <http://www.ntis.gov/ordernow>. Copies are available for inspection or copying for a fee from the NRC Public Document Room at 11555 Rockville Pike, Rockville, MD; the PDRs mailing address is USNRC PDR, Washington, DC 20555; telephone (301)415-4737 or (800)397-4209; fax (301)415-3548; email is PDR@NRC.GOV.

19

The determination of a DE for an ISFSI or MRS is consistent with the design approach 664 used in DOE Standard DOE-STD-1020, Natural Phenomena Hazards Design Evaluation 665 Criteria for Department of Energy Facilities,1 for similar type facilities.

666 Based on the preceding analysis, the NRC staff concludes that there is a reasonable 667 basis to design ISFSI or MRS SSCs for a single design earthquake, using a mean annual 668 probability of exceedance 5.0E-04, and adequately protect public health and safety.

669

20 APPENDIX C 670 DETERMINATION OF CONTROLLING EARTHQUAKES AND DEVELOPMENT 671 OF SEISMIC HAZARD INFORMATION BASE 672 C.1 INTRODUCTION 673 This appendix elaborates on the steps described in Regulatory Position 3 of this 674 regulatory guide to determine the controlling earthquakes used to define the Design Earthquake 675 Ground Motion (DE) at the site and to develop a seismic hazard information base. The 676 information base summarizes the contribution of individual magnitude and distance ranges to the 677 seismic hazard and the magnitude and distance values of the controlling earthquakes at 1 and 10 678 Hz. The controlling earthquakes are developed for the ground motion level corresponding to the 679 reference probability as defined in Appendix B to this regulatory guide.

680 The spectral ground motion levels, as determined from a probabilistic seismic hazard 681 analysis (PSHA), are used to scale a response spectrum shape. A site-specific response 682 spectrum shape is determined for the controlling earthquakes and local site conditions.

683 Regulatory Position 4 and Appendix F to this regulatory guide describe a procedure to determine 684 the DE using the controlling earthquakes and results from the PSHA.

685 C.2 PROCEDURE TO DETERMINE CONTROLLING EARTHQUAKES 686 The following approach is acceptable to the NRC staff for determining the controlling 687 earthquakes and developing a seismic hazard information base. This procedure is based on a 688 de-aggregation of the probabilistic seismic hazard in terms of earthquake magnitudes and 689 distances. When the controlling earthquakes have been obtained, the DE response spectrum 690 can be determined according to the procedure described in Appendix F to this regulatory guide.

691 Step 2-1 692 Perform a site-specific PSHA using the Lawrence Livermore National Laboratory (LLNL) 693 or Electric Power Research Institute (EPRI) methodologies (Refs. 1-3) for CEUS sites or perform 694 a site-specific PSHA for sites not in the CEUS or for sites for which LLNL or EPRI methods and 695 data are not applicable, for actual or assumed rock conditions. The hazard assessment (mean, 696 median, 85th percentile, and 15th percentile) should be performed for spectral accelerations at 1, 697 Hz, 10 Hz, and the peak ground acceleration. A lower-bound earthquake moment magnitude, M, 698 of 5.0 is recommended.

699 Step 2-2 700 Using the reference probability (5E-4/yr) as defined in Appendix B to this regulatory guide, 701 determine the ground motion levels for the spectral accelerations at 1 and 10 Hz from the total 702 mean hazard obtained in Step 2-1.

703 Step 2-3 704 Perform a complete PSHA for each of the magnitude-distance bins illustrated in Table 705 C.1. (These magnitude-distance bins are to be used in conjunction with the LLNL or EPRI 706 methods. For other situations, other binning schemes may be necessary.)

707

21 Table C.1 Recommended Magnitude and Distance Bins 708 Moment Magnitude Range of Bins 709 Distance 710 Range of Bin 711 (km) 712 5 - 5.5 5.5 - 6 6 - 6.5 6.5 - 7

>7 0 - 15 713 15 - 25 714 25 - 50 715 50 - 100 716 100 - 200 717 200 - 300 718

>300 719 Step 2-4 720 From the de-aggregated results of Step 2-3, the mean annual probability of exceeding the 721 ground motion levels of Step 2-2 (spectral accelerations at 1 and 10 Hz) are determined for each 722 magnitude-distance bin. These values are denoted by Hmdf1 for 1 Hz, and Hmdf10 for 10 Hz.

723 Using Hmdf values, the fractional contribution of each magnitude and distance bin to the 724 total hazard for the 1 Hz, P(m,d)1, is computed according to:

725 P(m,d)1 = Hmdf1/(

Hmdf1)

(Equation 1) 726 m d 727 The fractional contribution of each magnitude and distance bin to the total hazard for the 10 Hz, 728 P(m,d)10, is computed according to:

729 P(m,d)10 = Hmdf10/(

Hmdf10)

(Equation 2) 730 m d 731 Step 2-5 732 Review the magnitude-distance distribution for the 1 Hz frequency to determine whether 733 the contribution to the hazard for distances of 100 km (63 mi) or greater is substantial (on the 734 order of 5 percent or greater).

735 If the contribution to the hazard for distances of 100 km (63 mi) or greater exceeds 5 736 percent, additional calculations are needed to determine the controlling earthquakes using the 737 magnitude-distance distribution for distances greater than 100 km (63 mi). This distribution, 738 P>100(m,d)1, is defined by:

739 P>100(m,d)1 = P(m,d)1 /

P(m,d)1 (Equation 3) 740 m d>100 741

22 The purpose of this calculation is to identify a distant, larger event that may control low-742 frequency content of a response spectrum.

743 The distance of 100 km (63 mi) is chosen for CEUS sites. However, for all sites the 744 results of full magnitude-distance distribution should be carefully examined to ensure that proper 745 controlling earthquakes are clearly identified.

746 Step 2-6 747 Calculate the mean magnitude and distance of the controlling earthquake associated with 748 the ground motions determined in Step 2 for the 10 Hz frequency. The following relation is used 749 to calculate the mean magnitude using results of the entire magnitude-distance bins matrix:

750 Mc =
m
P(m, d)10 (Equation 4) 751 d m 752 where m is the central magnitude value for each magnitude bin.

753 The mean distance of the controlling earthquake is determined using results of the entire 754 magnitude-distance bins matrix:

755 756 Ln { Dc (10 Hz)} =
Ln (d)
P(m, d)10 (Equation 5) 757 d m 758 where d is the centroid distance value for each distance bin.

759 Step 2-7 760 If the contribution to the hazard calculated in Step 2-5 for distances of 100 km (63 mi) or 761 greater exceeds 5 percent for the 1 Hz frequency, calculate the mean magnitude and distance of 762 the controlling earthquakes associated with the ground motions determined in Step 2-2 for the 763 average of 1 Hz. The following relation is used to calculate the mean magnitude using 764 calculations based on magnitude-distance bins greater than distances of 100 km (63 mi) as 765 discussed in Step 2-5:

766 Mc (1Hz) =
m
P > 100 (m, d)1 (Equation 6) 767 m d>100 768 where m is the central magnitude value for each magnitude bin.

769 The mean distance of the controlling earthquake is based on magnitude-distance bins 770 greater than distances of 100 km as discussed in Step 2-5 and determined according to:

771 Ln { Dc (1 Hz)} =
Ln (d)
P(m, d)10 (Equation 7) 772 d>100 m 773 where d is the centroid distance value for each distance bin.

774 Step 2-8 775 Determine the DE response spectrum using the procedure described in Appendix F of this 776 regulatory guide.

777

23 C.3 EXAMPLE FOR A CEUS SITE 778 To illustrate the procedure in Section C.2, calculations are shown here for a CEUS site 779 using the 1993 LLNL hazard results (Refs. C.1, C.2). It must be emphasized that the 780 recommended magnitude and distance bins and procedure used to establish controlling 781 earthquakes were developed for application in the CEUS where the nearby earthquakes 782 generally control the response in the 10 Hz frequency range, and larger but distant events can 783 control the lower frequency range. For other situations, alternative binning schemes as well as a 784 study of contributions from various bins will be necessary to identify controlling earthquakes 785 consistent with the distribution of the seismicity.

786 Step 3-1 787 The 1993 LLNL seismic hazard methodology (Refs. C.1, C.2) was used to determine the 788 hazard at the site. A lower bound earthquake moment magnitude, M, of 5.0 was used in this 789 analysis. The analysis was performed for spectral acceleration at 1 and 10 Hz. The resultant 790 hazard curves are plotted in Figure C.1.

791 Step 3-2 792 The hazard curves at 1 and 10 Hz obtained in Step 1 are assessed at the reference 793 probability value of 5E-4/yr, as defined in Appendix B to this regulatory guide. The corresponding 794 ground motion level values are given in Table C.2. See Figure C.1.

795 Table C.2 Ground Motion Levels 796 Frequency (Hz) 797 1

10 Spectral Acc. (cm/s/s) 798 88 551 Step 3-3 799 The mean seismic hazard is de-aggregated for the matrix of magnitude and distance bins 800 as given in Table C.1.

801 A complete probabilistic hazard analysis was performed for each bin to determine the 802 contribution to the hazard from all earthquakes within the bin, i.e., all earthquakes with 803 earthquake moment magnitudes greater than 5.0 and distance from 0 km to greater than 300 km.

804 See Figure C.2 where the mean 1 Hz hazard curve is plotted for distance bin 25 - 50 km and 805 magnitude bin 6 - 6.5.

806 The hazard values corresponding to the ground motion levels, found in Step 2-2, and 807 listed in Table C.2, are then determined from the hazard curve for each bin for spectral 808 accelerations at 1 Hz and 10 Hz. This process is illustrated in Figure C.2. The vertical line 809 corresponds to the value 88 cm/s/s listed in Table C.2 for the 1 Hz hazard curve and intersects 810 the hazard curve for the 25 - 50 km distance bin, 6 - 6.5 magnitude bin, at a hazard value 811 (probability of exceedance) of 1.07E-06 per year. Tables C.3 and C.4 list the appropriate hazard 812 value for each bin for 1 Hz and 10 Hz frequencies respectively. It should be noted that if the 813 mean hazard in each of the 35 bins is added up it equals the reference probability of 5.0E-04.

814 815

24 Table C.3 Mean Exceeding Probability Values for Spectral Accelerations 816 at 1 Hz (88 cm/s/s) 817 Moment Magnitude Range of Bins Distance Range of Bin (km) 818 5 - 5.5 5.5 - 6 6 - 6.5 6.5 - 7

>7 0 - 15 819 9.68E-06 4.61E-05 0.0 0.0 0.0 15 - 25 820 0.0 1.26E-05 0.0 0.0 0.0 25 - 50 821 0.0 1.49E-05 1.05E-05 0.0 0.0 50 - 100 822 0.0 7.48E-06 3.65E-05 1.24E-05 0.0 100 - 200 823 0.0 1.15E-06 4.17E-05 2.98E-04 0.0 200 - 300 824 0.0 0.0 0.0 8.99E-06 0.0

> 300 825 0.0 0.0 0.0 0.0 0.0 Table C.4 Mean Exceeding Probability Values for Spectral Accelerations 826 at 10 Hz (551 cm/s/s) 827 Moment Magnitude Range of Bins Distance Range of Bin (km) 828 5 - 5.5 5.5 - 6 6 - 6.5 6.5 - 7

>7 0 - 15 829 1.68E-04 1.44E-04 2.39E-05 0.0 0.0 15 - 25 830 2.68E-05 4.87E-05 4.02E-06 0.0 0.0 25 - 50 831 5.30E-06 3.04E-05 2.65E-05 0.0 0.0 50 - 100 832 0.0 2.96E-06 8.84E-06 3.50E-06 0.0 100 - 200 833 0.0 0.0 0.0 7.08E-06 0.0 200 - 300 834 0.0 0.0 0.0 0.0 0.0

> 300 835 0.0 0.0 0.0 0.0 0.0 Note: The values of probabilities 1.0E-07 are shown as 0.0 in Tables C.3 and C.4.

836 Step 3-4 837 Using de-aggregated mean hazard results, the fractional contribution of each magnitude-838 distance pair to the total hazard is determined. Tables C.5 and C.6 show P(m,d)1 and P(m,d)10 839 for the 1 Hz and 10 Hz, respectively.

840 Step 3-5 841 Because the contribution of the distance bins greater than 100 km in Table C.5 contains 842 more than 5 percent of the total hazard for 1 Hz, the controlling earthquake for the 1 Hz 843 frequency will be calculated using magnitude-distance bins for distance greater than 100 km.

844 Table C.7 shows P>100 (m,d)1 for the 1 Hz frequency.

845 846

25 Table C.5 P(m,d)1 for Spectral Accelerations at 1 Hz 847 Corresponding to the Reference Probability 848 Moment Magnitude Range of Bins Distance Range of Bin (km) 849 5 - 5.5 5.5 - 6 6 - 6.5 6.5 - 7

>7 0 - 15 850 0.019 0.092 0.0 0.0 0.0 15 - 25 851 0.0 0.025 0.0 0.0 0.0 25 - 50 852 0.0 0.030 0.021 0.0 0.0 50 - 100 853 0.0 0.015 0.073 0.025 0.0 100 - 200 854 0.0 0.002 0.083 0.596 0.0 200 - 300 855 0.0 0.0 0.0 0.018 0.0

> 300 856 0.0 0.0 0.0 0.0 0.0 Figures C.3 to C.5 show the above information in terms of the relative percentage 857 contribution.

858 Table C.6 P(m,d)10 for Spectral Accelerations at 10 Hz 859 Corresponding to the Reference Probability 860 Moment Magnitude Range of Bins Distance Range of Bin (km) 861 5 - 5.5 5.5 - 6 6 - 6.5 6.5 - 7

>7 0 - 15 862 0.336 0.288 0.048 0.0 0.0 15 - 25 863 0.054 0.097 0.008 0.0 0.0 25 - 50 864 0.011 0.061 0.053 0.0 0.0 50 - 100 865 0.0 0.059 0.018 0.007 0.0 100 - 200 866 0.0 0.0 0.0 0.014 0.0 200 - 300 867 0.0 0.0 0.0 0.0 0.0

> 300 868 0.0 0.0 0.0 0.0 0.0 Table C.7 P>100 (m,d)1 for Spectral Acceleration at 1 Hz 869 Corresponding to the Reference Probability 870 Moment Magnitude Range of Bins Distance Range of Bin (km) 871 5 - 5.5 5.5 - 6 6 - 6.5 6.5 - 7

>7 100 - 200 872 0.0 0.003 0.119 0.852 0.0 200 - 300 873 0.0 0.0 0.0 0.026 0.0

>300 874 0.0 0.0 0.0 0.0 0.0 Note: The values of probabilities 1.0E-07 are shown as 0.0 in Tables C.5, C.6, and C.7.

875 Steps 3-6 and 3-7 876 To compute the controlling magnitudes and distances at 1 Hz and 10 Hz for the example 877 site, the values of P>100 (m,d)1 and P(m,d)10 are used with m and d values corresponding to the 878 mid-point of the magnitude of the bin (5.25, 5.75, 6.25, 6.75, 7.3) and centroid of the ring area 879 (10, 20.4, 38.9, 77.8, 155.6, 253.3, and somewhat arbitrarily 350 km). Note that the mid-point of 880

26 the last magnitude bin may change because this value is dependent on the maximum magnitudes 881 used in the hazard analysis. For this example site, the controlling earthquake characteristics 882 (magnitudes and distances) are given in Table C.8.

883 Step 3-8 884 The DE response spectrum is determined by the procedures described in Appendix F.

885 Figure C.1 886 Total Mean Hazard Curves 887 C.4 SITE 888 S NOT IN THE CEUS The 889 determination of the controlling 890 earthquakes and the seismic 891 hazard information base for sites not in the CEUS is also carried out using the procedure described in Section C.2 of this 892 appendix. However, because of differences in seismicity rates and ground motion attenuation at 893 these sites, alternative magnitude-distance bins may have to be used. An alternative reference 894 probability may also have to be developed, particularly for sites in the active plate margin region 895 and for sites at which a known tectonic structure dominates the hazard.

896

27 Table C.8 Magnitudes and Distances of Controlling Earthquakes 897 from the LLNL Probabilistic Analysis 898 1 Hz 899 10 Hz Mc and Dc > 100 km 900 Mc and Dc 6.7 and 157 km 901 5.9 and 18 km Figure C.2 1 Hz Mean Hazard Curve for 902 Distance Bin 25-50 km and Magnitude Bin 6-6.5 903 904 905

28 906 907 908 909 Figure C.3 910 Full 911 Distribution 912 of Hazard 913 for 10 Hz 914 5-5.5 5.5-6 6-6.5 6.5-7

>7 Magnitude Bins

29 915 916 917 918 919 920 Figure C.4 921 Full 922 Distribution of Hazard for 1 Hz 923 5-5.5 5.5-6 6-6.5 6.5-7

>7 Magnitude Bins

30 Figure C.5 924 Renormalized Hazard Distribution for 925 Distances Greater than 100 km for 1 Hz 926 5-5.5 5.5-6 6-6.5 6.5-7

>7 Magnitude Bins

1 Copies are available at current rates from the U.S. Government Printing Office, P.O. Box 37082, Washington, DC 20402-9328 (telephone (202)512-1800); or from the National Technical Information Service by writing NTIS at 5285 Port Royal Road, Springfield, VA 22161; <http://www.ntis.gov/ordernow>; telephone (703)487-4650. Copies are available for inspection or copying for a fee from the NRC Public Document Room at 11555 Rockville Pike, Rockville, MD; the PDRs mailing address is USNRC PDR, Washington, DC 20555; telephone (301)415-4737 or (800)397-4209; fax (301)415-3548; email is PDR@NRC.GOV.

2 Copies are available for inspection or copying for a fee from the NRC Public Document Room at 11555 Rockville Pike (first floor), Rockville, MD; the PDRs mailing address is USNRC PDR, Washington, DC 20555; telephone (301)415-4737 or 1-(800)397-4209; fax (301)415-3548; e-mail <PDR@NRC.GOV>.

31 REFERENCES 927 C.1 P. Sobel, "Revised Livermore Seismic Hazard Estimates for Sixty-Nine Nuclear Power 928 Plant Sites East of the Rocky Mountains, NUREG-1488, USNRC, April 1994.1 929 C.2 J.B. Savy et al., "Eastern Seismic Hazard Characterization Update," UCRL-ID-115111, 930 Lawrence Livermore National Laboratory, June 1993. (Accession number 9310190318 in 931 NRC's Public Document Room)2 932 C.3 Electric Power Research Institute (EPRI), "Probabilistic Seismic Hazard Evaluations at 933 Nuclear Power Plant Sites in the Central and Eastern United States," NP-4726, All 934 Volumes, 1989-1991.

935

32 APPENDIX D 936 GEOLOGICAL, SEISMOLOGICAL, AND GEOPHYSICAL INVESTIGATIONS TO 937 CHARACTERIZE SEISMIC SOURCES 938 D.1 INTRODUCTION 939 As characterized for use in probabilistic seismic hazard analyses (PSHA), seismic sources 940 are zones within which future earthquakes are likely to occur at the same recurrence rates.

941 Geological, seismological, and geophysical investigations provide the information needed to 942 identify and characterize source parameters, such as size and geometry, and to estimate 943 earthquake recurrence rates and maximum magnitudes. The amount of data available about 944 earthquakes and their causative sources varies substantially between the WUS (west of the 945 Rocky Mountain front) and the Central and Eastern United States (CEUS), or stable continental 946 region (SCR) (east of the Rocky Mountain front). Furthermore, there are variations in the amount 947 and quality of data within these regions.

948 In active tectonic regions there are both capable tectonic sources and seismogenic 949 sources, and because of their relatively high activity rate they may be more readily identified. In 950 the CEUS, identifying seismic sources is less certain because of the difficulty in correlating 951 earthquake activity with known tectonic structures, the lack of adequate knowledge about 952 earthquake causes, and the relatively lower activity rate. However, several significant tectonic 953 structures exist and some of these have been interpreted as potential seismogenic sources (e.g.,

954 the New Madrid fault zone, Nemaha Ridge, and Meers fault).

955 In the CEUS, there is no single recommended procedure to follow to characterize 956 maximum magnitudes associated with such candidate seismogenic sources; therefore, it is most 957 likely that the determination of the properties of the seismogenic source, whether it is a tectonic 958 structure or a seismotectonic province, will be inferred rather than demonstrated by strong 959 correlations with seismicity or geologic data. Moreover, it is not generally known what 960 relationships exist between observed tectonic structures in a seismic source within the CEUS and 961 the current earthquake activity that may be associated with that source. Generally, the observed 962 tectonic structure resulted from ancient tectonic forces that are no longer present. The historical 963 seismicity record, the results of regional and site studies, and judgment play key roles. If, on the 964 other hand, strong correlations and data exist suggesting a relationship between seismicity and 965 seismic sources, approaches used for more active tectonic regions can be applied.

966 The primary objective of geological, seismological, and geophysical investigations is to 967 develop an up-to-date, site-specific earth science data base that supplements existing 968 information (Ref. D.1). In the CEUS, the results of these investigations will also be used to 969 assess whether new data and their interpretation are consistent with the information used as the 970 basis for accepted probabilistic seismic hazard studies. If the new data are consistent with the 971 existing earth science data base, modification of the hazard analysis is not required. For sites in 972 the CEUS where there is significant new information (see Appendix E) provided by the site 973 investigation, and for sites in the WUS, site-specific seismic sources are to be determined. It is 974 anticipated that for most sites in the CEUS, new information will have been adequately bounded 975 by existing seismic source interpretations.

976 The following are to be evaluated for a seismic source for site-specific source 977 interpretations:

978

33 Seismic source location and geometry (location and extent, both surface and subsurface).

979 This evaluation will normally require interpretations of available geological, geophysical, 980 and seismological data in the source region by multiple experts or a team of experts. The 981 evaluation should include interpretations of the seismic potential of each source and 982 relationships among seismic sources in the region in order to express uncertainty in the 983 evaluations. Seismic source evaluations generally develop four types of sources: (1) 984 fault-specific sources, (2) area sources representing concentrated historic seismicity not 985 associated with known tectonic structure, (3) area sources representing geographic 986 regions with similar tectonic histories, type of crust, and structural features, and (4) 987 background sources. Background sources are generally used to express uncertainty in 988 the overall seismic source configuration interpreted for the site region. Acceptable 989 approaches for evaluating and characterizing uncertainties for input to a seismic hazard 990 calculation are contained in NUREG/CR-6372 (Ref. D.2).

991 Evaluations of earthquake recurrence for each seismic source, including recurrence rate 992 and recurrence model. These evaluations normally draw most heavily on historical and 993 instrumental seismicity associated with each source and paleoearthquake information.

994 Preferred methods and approaches for evaluating and characterizing uncertainty in 995 earthquake recurrence generally will depend on the type of source. Acceptable methods 996 are described in NUREG/CR-6372 (Ref. D.2).

997 Evaluations of the maximum earthquake magnitude for each seismic source. These 998 evaluations will draw on a broad range of source-specific tectonic characteristics, 999 including tectonic history and available seismicity data. Uncertainty in this evaluation 1000 should normally be expressed as a maximum magnitude distribution. Preferred methods 1001 and information for evaluating and characterizing maximum earthquakes for seismic 1002 sources vary with the type of source. Acceptable methods are contained in NUREG/CR-1003 6372 (Ref. D.2).

1004 Other evaluations, depending on the geologic setting of a site, such as local faults that 1005 have a history of Quaternary (last 2 million years) displacements, sense of slip on faults, 1006 fault length and width, area of faults, age of displacements, estimated displacement per 1007 event, estimated earthquake magnitude per offset event, orientations of regional tectonic 1008 stresses with respect to faults, and the possibility of seismogenic folds. Capable tectonic 1009 sources are not always exposed at the ground surface in the WUS as demonstrated by 1010 the buried reverse causative faults of the 1983 Coalinga, 1988 Whittier Narrows, l989 1011 Loma Prieta, and 1994 Northridge earthquakes. These examples emphasize the need to 1012 conduct thorough investigations not only at the ground surface but also in the subsurface 1013 to identify structures at seismogenic depths. Whenever faults or other structures are 1014 encountered at a site (including sites in the CEUS) in either outcrop or excavations, it is 1015 necessary to perform adequately detailed specific investigations to determine whether or 1016 not they are seismogenic or may cause surface deformation at the site. Acceptable 1017 methods for performing these investigations are contained in NUREG/CR-5503 (Ref. D.3).

1018 Effects of human activities such as withdrawal of fluid from or addition of fluid to the 1019 subsurface associated with mining or the construction of dams and reservoirs.

1020 Volcanic hazard is not addressed in this regulatory guide and will be considered on a 1021 case-by-case basis in regions where a potential for this hazard exists. For sites where 1022 volcanic hazard is evaluated, earthquake sources associated with volcanism should be 1023

34 evaluated and included in the seismic source interpretations input to the hazard 1024 calculation.

1025 D.2.

INVESTIGATIONS TO EVALUATE SEISMIC SOURCES 1026 D.2.1 General 1027 1028 Investigations of the site and region around the site are necessary to identify both 1029 seismogenic sources and capable tectonic sources and to determine their potential for generating 1030 earthquakes and causing surface deformation. If it is determined that surface deformation need 1031 not be taken into account at the site, sufficient data to clearly justify the determination should be 1032 presented in the application for an early site permit, construction permit, operating license, or 1033 combined license. Generally, any tectonic deformation at the earths surface within 40 km (25 1034 miles) of the site will require detailed examination to determine its significance. Potentially active 1035 tectonic deformation within the seismogenic zone beneath a site will have to be assessed using 1036 geophysical and seismological methods to determine its significance.

1037 Engineering solutions are generally available to mitigate the potential vibratory effects of 1038 earthquakes through design. However, engineering solutions cannot always be demonstrated to 1039 be adequate for mitigation of the effects of permanent ground displacement phenomena such as 1040 surface faulting or folding, subsidence, or ground collapse. For this reason, it is prudent to select 1041 an alternative site when the potential for permanent ground displacement exists at the proposed 1042 site (Ref. D.4).

1043 In most of the CEUS, instrumentally located earthquakes seldom bear any relationship to 1044 geologic structures exposed at the ground surface. Possible geologically young fault 1045 displacements either do not extend to the ground surface or there is insufficient geologic material 1046 of the appropriate age available to date the faults. Capable tectonic sources are not always 1047 exposed at the ground surface in the WUS, as demonstrated by the buried (blind) reverse 1048 causative faults of the 1983 Coalinga, 1988 Whittier Narrows, 1989 Loma Prieta, and 1994 1049 Northridge earthquakes. These factors emphasize the need to conduct thorough investigations 1050 not only at the ground surface but also in the subsurface to identify structures at seismogenic 1051 depths.

1052 The level of detail for investigations should be governed by knowledge of the current and 1053 late Quaternary tectonic regime and the geological complexity of the site and region. The 1054 investigations should be based on increasing the amount of detailed information as they proceed 1055 from the regional level down to the site area [e.g., 320 km (200 mi) to 8 km (5 mi) distance from 1056 the site]. Whenever faults or other structures are encountered at a site (including sites in the 1057 CEUS) in either outcrop or excavations, it is necessary to perform many of the investigations 1058 described below to determine whether or not they are capable tectonic sources.

1059 The investigations for determining seismic sources should be carried out at three levels, 1060 with areas described by radii of 320 km (200 mi), 40 km (25 mi), and 8 km (5 mi) from the site.

1061 The level of detail increases closer to the site. The specific site, to a distance of at least 1 km 1062 (0.6 mi), should be investigated in more detail than the other levels.

1063 The regional investigations [within a radius of 320 km (200 mi) of the site] should be 1064 planned to identify seismic sources and describe the Quaternary tectonic regime. The data 1065 should be presented at a scale of 1:500,000 or smaller. The investigations are not expected to 1066

35 be extensive or in detail, but should include a comprehensive literature review supplemented by 1067 focused geological reconnaissances based on the results of the literature study (including 1068 topographic, geologic, aeromagnetic, and gravity maps and airphotos). Some detailed 1069 investigations at specific locations within the region may be necessary if potential capable 1070 tectonic sources or seismogenic sources that may be significant for determining the safe 1071 shutdown earthquake ground motion are identified.

1072 The large size of the area for the regional investigations is recommended because of the 1073 possibility that all significant seismic sources, or alternative configurations, may not have been 1074 enveloped by the LLNL/EPRI data base. Thus, it will increase the chances of (1) identifying 1075 evidence for unknown seismic sources that might extend close enough for earthquake ground 1076 motions generated by that source to affect the site and (2) confirming the PSHAs data base.

1077 Furthermore, because of the relatively aseismic nature of the CEUS, the area should be large 1078 enough to include as many historical and instrumentally recorded earthquakes for analysis as 1079 reasonably possible. The specified area of study is expected to be large enough to incorporate 1080 any previously identified sources that could be analogous to sources that may underlie or be 1081 relatively close to the site. In past licensing activities for sites in the CEUS, it has often been 1082 necessary, because of the absence of datable horizons overlying bedrock, to extend 1083 investigations out many tens or hundreds of kilometers from the site along a structure or to an 1084 outlying analogous structure in order to locate overlying datable strata or unconformities so that 1085 geochronological methods could be applied. This procedure has also been used to estimate the 1086 age of an undatable seismic source in the site vicinity by relating its time of last activity to that of 1087 a similar, previously evaluated structure, or a known tectonic episode, the evidence of which may 1088 be many tens or hundreds of miles away.

1089 In the WUS it is often necessary to extend the investigations to great distances (up to 1090 hundreds of kilometers) to characterize a major tectonic structure, such as the San Gregorio-1091 Hosgri Fault Zone and the Juan de Fuca Subduction Zone. On the other hand, in the WUS it is 1092 not usually necessary to extend the regional investigations that far in all directions. For example, 1093 for a site such as Diablo Canyon, which is near the San Gregorio-Hosgri Fault, it would not be 1094 necessary to extend the regional investigations farther east than the dominant San Andreas 1095 Fault, which is about 75 km (45 mi) from the site; nor west beyond the Santa Lucia Banks Fault, 1096 which is about 45 km (27 mi). Justification for using lesser distances should be provided.

1097 Reconnaissance-level investigations, which may need to be supplemented at specific 1098 locations by more detailed explorations such as geologic mapping, geophysical surveying, 1099 borings, and trenching, should be conducted to a distance of 40 km (25 mi) from the site; the data 1100 should be presented at a scale of 1:50,000 or smaller.

1101 Detailed investigations should be carried out within a radius of 8 km (5 mi) from the site, 1102 and the resulting data should be presented at a scale of 1:5,000 or smaller. The level of 1103 investigations should be in sufficient detail to delineate the geology and the potential for tectonic 1104 deformation at or near the ground surface. The investigations should use the methods described 1105 in subsections D.2.2 and D.2.3 that are appropriate for the tectonic regime to characterize 1106 seismic sources.

1107 The areas of investigations may be asymmetrical and may cover larger areas than those 1108 described above in regions of late Quaternary activity, regions with high rates of historical seismic 1109 activity (felt or instrumentally recorded data), or sites that are located near a capable tectonic 1110 source such as a fault zone.

1111

36 Data from investigations at the site (approximately 1 km2) should be presented at a scale 1112 of 1:500 or smaller. Important aspects of the site investigations are the excavation and logging of 1113 exploratory trenches and the mapping of the excavations for the plant structures, particularly 1114 plant structures that are characterized as Seismic Category I. In addition to geological, 1115 geophysical, and seismological investigations, detailed geotechnical engineering investigations, 1116 as described in Regulatory Guide 1.132 (Ref. D.5) and NUREG/CR-5738 (Ref. D.6), should be 1117 conducted at the site.

1118 The investigations needed to assess the suitability of the site with respect to effects of 1119 potential ground motions and surface deformation should include determination of (1) the 1120 lithologic, stratigraphic, geomorphic, hydrologic, geotechnical, and structural geologic 1121 characteristics of the site and the area surrounding the site, including its seismicity and geological 1122 history, (2) geological evidence of fault offset or other distortion such as folding at or near ground 1123 surface within the site area (8 km radius), and (3) whether or not any faults or other tectonic 1124 structures, any part of which are within a radius of 8 km (5 mi) from the site, are capable tectonic 1125 sources. This information will be used to evaluate tectonic structures underlying the site area, 1126 whether buried or expressed at the surface, with regard to their potential for generating 1127 earthquakes and for causing surface deformation at or near the site. This part of the evaluation 1128 should also consider the possible effects caused by human activities such as withdrawal of fluid 1129 from or addition of fluid to the subsurface, extraction of minerals, or the loading effects of dams 1130 and reservoirs.

1131 D.2.2 Reconnaissance Investigations, Literature Review, and Other Sources of 1132 Preliminary Information 1133 Regional literature and reconnaissance-level investigations should be planned based on 1134 reviews of available documents and the results of previous investigations. Possible sources of 1135 information, in addition to refereed papers published in technical journals, include universities, 1136 consulting firms, and government agencies. The following guidance is provided but it is not 1137 considered all-inclusive. Some investigations and evaluations will not be applicable to every site, 1138 and situations may occur that require investigations that are not included in the following 1139 discussion. In addition, it is anticipated that new technologies will be available in the future that 1140 will be applicable to these investigations.

1141 D.2.3 Detailed Site Vicinity and Site Area Investigations 1142 The following methods are suggested but they are not all-inclusive and investigations 1143 should not be limited to them. Some procedures will not be applicable to every site, and 1144 situations will occur that require investigations that are not included in the following discussion. It 1145 is anticipated that new technologies will be available in the future that will be applicable to these 1146 investigations.

1147 D.2.3.1 Surface Investigations 1148 Surface exploration to assess the geology and geologic structure of the site area is 1149 dependent on the site location and may be carried out with the use of any appropriate 1150 combination of the geological, geophysical, and seismological techniques summarized in the 1151 following paragraphs. However, not all of these methods must be carried out at a given site.

1152 D.2.3.1.1. Geological interpretations should be performed of aerial photographs and other 1153 remote-sensing as appropriate for the particular site conditions, to assist in identifying rock 1154

37 outcrops, faults and other tectonic features, fracture traces, geologic contacts, lineaments, soil 1155 conditions, and evidence of landslides or soil liquefaction.

1156 D.2.3.1.2. Mapping topographic, geomorphic, and hydrologic features should be 1157 performed at scales and with contour intervals suitable for analysis and descriptions of 1158 stratigraphy (particularly Quaternary), surface tectonic structures such as fault zones, and 1159 Quaternary geomorphic features. For coastal sites or sites located near lakes or rivers, this 1160 includes topography, geomorphology (particularly mapping marine and fluvial terraces),

1161 bathymetry, geophysics (such as seismic reflection), and hydrographic surveys to the extent 1162 needed to describe the site area features.

1163 D.2.3.1.3. Vertical crustal movements should be evaluated using: (1) geodetic land 1164 surveying and (2) geological analyses (such as analysis of regional dissection and degradation 1165 patterns), marine and lacustrine terraces and shorelines, fluvial adjustments (such as changes in 1166 stream longitudinal profiles or terraces), and other long-term changes (such as elevation changes 1167 across lava flows).

1168 D.2.3.1.4. Analysis should be performed to determine the tectonic significance of offset, 1169 displaced, or anomalous landforms such as displaced stream channels or changes in stream 1170 profiles or the upstream migration of knick-points; abrupt changes in fluvial deposits or terraces; 1171 changes in paleo-channels across a fault; or uplifted, down-dropped, or laterally displaced marine 1172 terraces.

1173 D.2.3.1.5. Analysis should be performed to determine the tectonic significance of 1174 Quaternary sedimentary deposits within or near tectonic zones such as fault zones, including (1) 1175 fault-related or fault-controlled deposits such as sag ponds, graben fill deposits, and colluvial 1176 wedges formed by the erosion of a fault paleo-scarp, and (2) non-fault-related, but offset, 1177 deposits such as alluvial fans, debris cones, fluvial terrace, and lake shoreline deposits.

1178 D.2.3.1.6. Identification and analysis should be performed of deformation features caused 1179 by vibratory ground motions, including seismically induced liquefaction features (sand boils, 1180 explosion craters, lateral spreads, settlement, soil flows), mud volcanoes, landslides, rockfalls, 1181 deformed lake deposits or soil horizons, shear zones, cracks or fissures.

1182 D.2.3.1.7. Analysis should be performed of fault displacements, including the 1183 interpretation of the morphology of topographic fault scarps associated with or produced by 1184 surface rupture. Fault scarp morphology is useful for estimating the age of last displacement (in 1185 conjunction with the appropriate geochronological methods described NUREG/CR-5562 (Ref.

1186 D.6), approximate magnitude of the associated earthquake, recurrence intervals, slip rate, and 1187 the nature of the causative fault at depth.

1188 D.2.3.2 Subsurface Investigations at the Site [within 1 km (0.5 mi)]

1189 Subsurface investigations at the site to identify and describe potential seismogenic 1190 sources or capable tectonic sources and to obtain required geotechnical information are 1191 described in Regulatory Guide 1.132 (Ref. D.5) and updated in NUREG/CR-5738 (Ref. D.7). The 1192 investigations include, but may not be confined to, the following:

1193 D.2.3.2.1. Geophysical investigations that have been useful in the past include magnetic 1194 and gravity surveys, seismic reflection and seismic refraction surveys, bore-hole geophysics, 1195 electrical surveys, and ground-penetrating radar surveys.

1196 1197

38 D.2.3.2.2. Core borings to map subsurface geology and obtain samples for testing such 1198 as determining the properties of the subsurface soils and rocks and geochronological analysis; 1199 D.2.3.2.3. Excavation and logging of trenches across geological features to obtain 1200 samples for the geochronological analysis of those features.

1201 D.2.3.2.4. At some sites, deep unconsolidated material/soil, bodies of water, or other 1202 material may obscure geologic evidence of past activity along a tectonic structure. In such cases, 1203 the analysis of evidence elsewhere along the structure can be used to evaluate its characteristics 1204 in the vicinity of the site.

1205 In the CEUS it may not be possible to reasonably demonstrate the age of youngest 1206 activity on a tectonic structure with adequate deterministic certainty. In such cases the 1207 uncertainty should be quantified; the NRC staff will accept evaluations using the methods 1208 described in NUREG/CR-5503 (Ref. D.3). A demonstrated tectonic association of such 1209 structures with geologic structural features or tectonic processes that are geologically old (at least 1210 pre-Quaternary) should be acceptable as an age indicator in the absence of conflicting evidence.

1211 D.2.3.3 Surface-Fault Rupture and Associated Deformation at the Site 1212 A site that has a potential for fault rupture at or near the ground surface and associated 1213 deformation should be avoided. Where it is determined that surface deformation need not be 1214 taken into account, sufficient data or detailed studies to reasonably support the determination 1215 should be presented. Requirements for setback distance from active faults for hazardous waste 1216 treatment, storage and disposal facilities can be found in U.S. Environmental Protection Agency 1217 regulations (40 CFR Part 264).

1218 The presence or absence of Quaternary faulting at the site needs to be evaluated to 1219 determine whether there is a potential hazard that is due to surface faulting. The potential for 1220 surface fault rupture should be characterized by evaluating (1) the location and geometry of faults 1221 relative to the site, (2) nature and amount of displacement (sense of slip, cumulative slip, slip per 1222 event, and nature and extent of related folding and/or secondary faulting), and (3) the likelihood 1223 of displacement during some future period of concern (recurrence interval, slip rate, and elapsed 1224 time since the most recent displacement). Acceptable methods and approaches for conducting 1225 these evaluations are described in NUREG/CR-5503 (Ref. D.3); acceptable geochronology dating 1226 methods are described in NUREG/CR-5562 (Ref. D.7).

1227 For assessing the potential for fault displacement, the details of the spatial pattern of the 1228 fault zone (e.g., the complexity of fault traces, branches, and en echelon patterns) may be 1229 important as they may define the particular locations where fault displacement may be expected 1230 in the future. The amount of slip that might be expected to occur can be evaluated directly based 1231 on paleoseismic investigations or it can be estimated indirectly based on the magnitude of the 1232 earthquake that the fault can generate.

1233 Both non-tectonic and tectonic deformation can pose a substantial hazard to an ISFSI or 1234 MRS, but there are likely to be differences in the approaches used to resolve the issues raised by 1235 the two types of phenomena. Therefore, non-tectonic deformation should be distinguished from 1236 tectonic deformation at a site. In past nuclear power plant licensing activities, surface 1237 displacements caused by phenomena other than tectonic phenomena have been confused with 1238 tectonically induced faulting. Such structures, such as found in karst terrain; and growth faulting, 1239 occurring in the Gulf Coastal Plain or in other deep soil regions, cause extensive subsurface fluid 1240 withdrawal.

1241

39 Glacially induced faults generally do not represent a deep-seated seismic or fault 1242 displacement hazard because the conditions that created them are no longer present. However, 1243 residual stresses from Pleistocene glaciation may still be present in glaciated regions, although 1244 they are of less concern than active tectonically induced stresses. These features should be 1245 investigated with respect to their relationship to current in situ stresses.

1246 The nature of faults related to collapse features can usually be defined through 1247 geotechnical investigations and can either be avoided or, if feasible, adequate engineering fixes 1248 can be provided.

1249 Large, naturally occurring growth faults as found in the coastal plain of Texas and 1250 Louisiana can pose a surface displacement hazard, even though offset most likely occurs at a 1251 much less rapid rate than that of tectonic faults. They are not regarded as having the capacity to 1252 generate damaging vibratory ground motion, can often be identified and avoided in siting, and 1253 their displacements can be monitored. Some growth faults and antithetic faults related to growth 1254 faults and fault zones should be applied in regions where growth faults are known to be present.

1255 Local human-induced growth faulting can be monitored and controlled or avoided.

1256 If questionable features cannot be demonstrated to be of non-tectonic origin, they should 1257 be treated as tectonic deformation.

1258 D.2.4 Site Geotechnical Investigations and Evaluations 1259 D.2.4.1 Geotechnical Investigations 1260 The geotechnical investigations should include, but not necessarily be limited to, (1) 1261 defining site soil and near-surface geologic strata properties as may be required for hazard 1262 evaluations, engineering analyses, and seismic design, (2) evaluating the effects of local soil and 1263 site geologic strata on ground motion at the ground surface, (3) evaluating dynamic properties of 1264 the near-surface soils and geologic strata, (4) conducting soil-structure interaction analyses, and 1265 (5) assessing the potential for soil failure or deformation induced by ground shaking (liquefaction, 1266 differential compaction, land sliding).

1267 The extent of investigation to determine the geotechnical characteristics of a site depends 1268 on the site geology and subsurface conditions. By working with experienced geotechnical 1269 engineers and geologists, an appropriate scope of investigations can be developed for a 1270 particular facility following the guidance contained in Regulatory Guide 1.132 (Ref. D.5) updated 1271 with NUREG/CR-5738 (Ref. D.6). The extent of subsurface investigations is dictated by the 1272 foundation requirements and by the complexity of the anticipated subsurface conditions. The 1273 locations and spacing of borings, soundings, and exploratory excavations should be chosen to 1274 adequately define subsurface conditions. Subsurface explorations should be chosen to 1275 adequately define subsurface conditions; exploration sampling points should be located to permit 1276 the construction of geological cross sections and soil profiles through foundations of safety-1277 related structures and other important locations at the site.

1278 Sufficient geophysical and geotechnical data should be obtained to allow for reasonable 1279 assessments of representative soil profile and soil parameters and to reasonably quantify 1280 variability. The guidance found in Regulatory Guide 1.132 (Ref. D.5) and NUREG/CR-5738 (Ref.

1281 D.6) is acceptable. In general, this guidance should be adapted to the requirements of the site to 1282 establish the scope of geotechnical investigations for the site as well as the appropriate methods 1283 that will be used.

1284

40 For ISFSIs co-located with existing nuclear plants, site investigations should be conducted 1285 if the existing site information is not available or insufficient. Soil/rock profiles (cross-sections) at 1286 the locations of the facilities should be provided based on the results of site investigations. The 1287 properties required are intimately linked to the designs and evaluations to be conducted. For 1288 example, for analyses of soil response effects, assessment of strain dependent-soil-dynamic 1289 modulus and damping characteristics are required. An appropriate site investigation program 1290 should be developed in consultation with the geotechnical engineering representative of the 1291 project team.

1292 Subsurface conditions should be investigated by means of borings, soundings, well logs, 1293 exploratory excavations, sampling, geophysical methods (e.g., cross-hole, down-hole, and 1294 geophysical logging) that adequately assess soil and ground water conditions and other methods 1295 described in NUREG/CR-5738 (Ref. D.6). Appropriate investigations should be made to 1296 determine the contribution of the subsurface soils and rocks to the loads imposed on the 1297 structures.

1298 A laboratory testing program should be carried out to identify and classify the subsurface 1299 soils and rocks and to determine their physical and engineering properties. Laboratory tests for 1300 both static and dynamic properties (e.g., shear modulus, damping, liquefaction resistance, etc.)

1301 are generally required. The dynamic property tests should include, as appropriate, cyclic triaxial 1302 tests, cyclic simple shear tests, cyclic torsional shear tests, and resonant column tests. Both 1303 static and dynamic tests should be conducted as recommended in American Society for Testing 1304 and Materials (ASTM) standards or test procedures acceptable to the staff. The ASTM 1305 specification numbers for static and dynamic laboratory tests can be found in the annual books of 1306 ASTM Standards, Volume 04.08. Examples of soil dynamic property and strength tests are 1307 shown in Table D.1. Sufficient laboratory test data should be obtained to allow for reasonable 1308 assessments of mean values of soil properties and their potential variability.

1309 For coarse geological materials such as coarse gravels and sand-gravel mixtures, special 1310 testing equipment and testing facility should be used. Larger sample size is required for 1311 laboratory tests on this type of materials (e.g., samples with 12-inch diameter were used in the 1312 Rockfalls Testing Facility). It is generally difficult to obtain in situ undisturbed samples of 1313 unconsolidated gravelly soils for laboratory tests. If it is not feasible to collect test samples and, 1314 thus, no laboratory test results are available, the dynamic properties should be estimated from 1315 the published data of similar gravelly soils.

1316 Table D.1 Examples of Soil Dynamic Property and Strength Tests 1317 D 3999-91 1318 (Ref. D.8) 1319 Standard Test Method for the Determination of the Modulus and Damping Properties of Soils Using the Cyclic Triaxial Apparatus D 4015-92 1320 (Ref. D.9) 1321 Standard Test Methods for Modulus and Damping of Soils by the Resonant-Column Method D 5311-92 1322 (Ref. D10) 1323 Standard Test Method for Load-Controlled Cyclic Triaxial Strength of Soil D.2.4.2 Seismic Wave Transmission Characteristics of the Site 1324 To be acceptable, the seismic wave transmission characteristics (spectral amplification or 1325 deamplification) of the materials overlying bedrock at the site are described as a function of the 1326

41 significant structural frequencies. The following material properties should be determined for 1327 each stratum under the site: (1) thickness, seismic compressional and shear wave velocities, (2) 1328 bulk densities, (3) soil index properties and classification, (4) shear modulus and damping 1329 variations with strain level, and (5) the water table elevation and its variation throughout the site.

1330 Where vertically propagating shear waves may produce the maximum ground motion, a 1331 one-dimensional equivalent-linear analysis or nonlinear analysis may be appropriate. Where 1332 horizontally propagating shear waves, compressional waves, or surface waves may produce the 1333 maximum ground motion, other methods of analysis may be more appropriate. However, since 1334 some of the variables are not well defined and investigative techniques are still in the 1335 developmental stage, no specific generally agreed-upon procedures can be recommended at this 1336 time. Hence, the staff must use discretion in reviewing any method of analysis. To ensure 1337 appropriateness, site response characteristics determined from analytical procedures should be 1338 compared with historical and instrumental earthquake data, when such data are available.

1339 D.2.4.3 Site Response Analysis for Soil Sites 1340 As part of quantification of earthquake ground motions at an ISFSI or MRS site, an 1341 analysis of soil response effects on ground motions should be performed. A specific analysis is 1342 not required at a hard rock site. Site response analyses (often referred to as site amplification 1343 analyses) are relatively more important when the site surficial soil layer is a soft clay and/or when 1344 there is a high stiffness contrast (wave velocity contrast) between a shallow soil layer and 1345 underlying bedrock. Such conditions have shown strong local soil effects on ground motion. Site 1346 response analyses are always important for sites that have predominant frequencies within the 1347 range of interest for the DE ground motions. Thus, the stiffness of the soil and bedrock as well 1348 as the depth of soil deposit should be carefully evaluated.

1349 In performing a site response analysis, the ground motions (usually acceleration time 1350 histories) defined at bedrock or outcrop are propagated through an analytical model of the site 1351 soils to determine the influence of the soils on the ground motions. The required soil parameters 1352 for the site response analysis include the depth, soil type, density, shear modulus and damping, 1353 and their variations with strain levels for each of the soil layers. Internal friction angle, cohesive 1354 strength, and over-consolidation ratio for clay are also needed for non-linear analyses. The strain 1355 dependent shear modulus and damping curves should be developed based on site-specific 1356 testing results and supplemented as appropriate by published data for similar soils. The effects 1357 of confining pressures (that reflect the depths of the soil) on these strain-dependent soil dynamic 1358 characteristics should be assessed and considered in site response analysis. The variability in 1359 these properties should be accounted in the site response analysis. The results of the site 1360 response analysis should show the input motion (rock response spectra), output motion (surface 1361 response spectra), and spectra amplification function (site ground motion transfer function).

1362 D.2.4.4 Ground Motion Evaluations 1363 D.2.4.4.1. Liquefaction is a soil behavior phenomenon in which cohesionless soils (sand, 1364 silt, or gravel) under saturated conditions lose a substantial part or all of their strength because of 1365 high pore water pressures generated in the soils by strong ground motions induced by 1366 earthquakes. Potential effects of liquefaction include reduction in foundation bearing capacity, 1367 settlements, land sliding and lateral movements, flotation of lightweight structures (such as tanks) 1368 embedded in the liquefied soil, and increased lateral pressures on walls retaining liquefied soil.

1369 Guidance in Draft Regulatory Guide DG-1105, Procedures and Criteria for Assessing Seismic 1370 Soil Liquefaction at Nuclear Power Plant Sites (Ref. D.11), is being developed to be used for 1371 evaluating the site for liquefaction potential.

1372

42 Investigations of liquefaction potential typically involve both geological and geotechnical 1373 engineering assessments. The parameters controlling liquefaction phenomena are (1) the 1374 lithology of the soil at the site, (2) the ground water conditions, (3) the behavior of the soil under 1375 dynamic loadings, and (4) the potential severity of the vibratory ground motion. The following 1376 site-specific data should be acquired and used along with state-of-the-art evaluation procedures 1377 (e.g., Ref. D.12, Ref. D.13).

1378 Soil grain size distribution, density, static and dynamic strength, stress history, and 1379 geologic age of the sediments; 1380 Ground water conditions; 1381 Penetration resistance of the soil, e.g., Standard Penetration Test (SPT), Cone 1382 Penetration Test (CPT);

1383 Shear wave velocity of the soil velocity of the soil; 1384 Evidence of past liquefaction; and 1385 Ground motion characteristics.

1386 A soil behavior phenomenon similar to liquefaction is strength reduction in sensitive clays.

1387 Although this behavior phenomenon is relatively rare in comparison to liquefaction, it should not 1388 be overlooked as a potential cause for land sliding and lateral movements. Therefore, the 1389 existence of sensitive clays at the site should be identified.

1390 D.2.4.4.2. Ground settlement during and after an earthquake that is due to dynamic loads, 1391 change of ground water conditions, soil expansion, soil collapse, erosion, and other causes must 1392 be considered. Ground settlement that is due to the ground shaking induced by an earthquake 1393 can be caused by two factors: (1) compaction of dry sands by ground shaking and (2) 1394 settlement caused by dissipation of dynamically induced pore water in saturated sands.

1395 Differential settlement would cause more damage to facilities than would uniform settlement.

1396 Differential compaction of cohesionless soils and resulting differential ground settlement can 1397 accompany liquefaction or may occur in the absence of liquefaction. The same types of geologic 1398 information and soil data used in liquefaction potential assessments, such as the SPT value, can 1399 also be used in assessing the potential for differential compaction. Ground subsidence has been 1400 observed at the surface above relatively shallow cavities formed by mining activities (particularly 1401 coal mines) and where large quantities of salt, oil, gas, or ground water have been extracted (Ref.

1402 D.14). Where these conditions exist near a site, consideration and investigation must be given to 1403 the possibility that surface subsidence will occur.

1404 D.2.4.4.3. The stability of natural and man-made slopes must be evaluated when their 1405 failures would affect the safety and operation of an ISFSI or MRS. In addition to land sliding 1406 facilitated by liquefaction-induced strength reduction, instability and deformation of hillside and 1407 embankment slopes can occur from the ground shaking inertia forces causing a temporary 1408 exceedance of the strength of soil or rock. The slip surfaces of previous landslides, weak planes 1409 or seams of subsurface materials, mapping and dating paleo-slope failure events, loss of shear 1410 strength of the materials caused by the natural phenomena hazards such as liquefaction or 1411 reduction of strength due to wetting, hydrological conditions including pore pressure and 1412 seepage, and loading conditions imposed by the natural phenomena events must all be 1413 considered in determining the potential for instability and deformations. Various possible modes 1414

43 of failure should be considered. Both static and dynamic analyses must be performed for the 1415 stability of the slopes.

1416 The following information, at a minimum, is to be collected for the evaluation of slope 1417 instability:

1418 Slope cross sections covering areas that would be affected the slope stability; 1419 Soil and rock profiles within the slope cross sections; 1420 Static and dynamic soil and rock properties, including densities, strengths, and 1421 deformability; 1422 Hydrological conditions and their variations; and 1423 Rock fall events.

1424 D.2.5 Geochronology 1425 An important part of the geologic investigations to identify and define potential seismic 1426 sources is the geochronology of geologic materials. An acceptable classification of dating 1427 methods is based on the rationale described in Reference D.15. The following techniques, which 1428 are presented according to that classification, are useful in dating Quaternary deposits.

1429 D.2.5.1 Sidereal Dating Methods 1430 Dendrochronology 1431 Varve chronology 1432 1433 Schlerochronology 1434 1435 D.2.5.2 Isotopic Dating Methods 1436 Radiocarbon 1437 Cosmogenic nuclides - 36Cl, 10Be, 21Pb, and 26Al 1438 Potassium argon and argon-39-argon-40 1439 Uranium series - 234U-230Th and 235U-231Pa 1440 210Lead 1441 Uranium-lead, thorium-lead 1442 D.2.5.3 Radiogenic Dating Methods 1443 Fission track 1444 Luminescence 1445

44 1446 Electron spin resonance 1447 D.2.5.4 Chemical and Biological Dating Methods 1448 Amino acid racemization 1449 Obsidian and tephra hydration 1450 Lichenometry 1451 D.2.5.6 Geomorphic Dating Methods 1452 Soil profile development 1453 Rock and mineral weathering 1454 Scarp morphology 1455 D.2.5.7 Correlation Dating Methods 1456 Paleomagnetism (secular variation and reversal stratigraphy) 1457 Tephrochronology 1458 Paleontology (marine and terrestrial) 1459 Global climatic correlations - Quaternary deposits and landforms, marine stable isotope 1460 records, etc.

1461 In the CEUS, it may not be possible to reasonably demonstrate the age of last activity of a 1462 tectonic structure. In such cases the NRC staff will accept association of such structures with 1463 geologic structural features or tectonic processes that are geologically old (at least pre-1464 Quaternary) as an age indicator in the absence of conflicting evidence.

1465 These investigative procedures should also be applied, where possible, to characterize 1466 offshore structures (faults or fault zones, and folds, uplift, or subsidence related to faulting at 1467 depth) for coastal sites or those sites located adjacent to landlocked bodies of water.

1468 Investigations of offshore structures will rely heavily on seismicity, geophysics, and bathymetry 1469 rather than conventional geologic mapping methods that normally can be used effectively 1470 onshore. However, it is often useful to investigate similar features onshore to learn more about 1471 the significant offshore features.

1472

1 Copies are available at current rates from the U.S. Government Printing Office, P.O. Box 37082, Washington, DC 20402-9328 (telephone (202)512-1800); or from the National Technical Information Service by writing NTIS at 5285 Port Royal Road, Springfield, VA 22161; (telephone (703)487-4650; <http://www.ntis.gov/ordernow>. Copies are available for inspection or copying for a fee from the NRC Public Document Room at 11555 Rockville Pike, Rockville, MD; the PDRs mailing address is USNRC PDR, Washington, DC 20555; telephone (301)415-4737 or (800)397-4209; fax (301)415-3548; email is PDR@NRC.GOV.1.

2 Requests for single copies of draft or active regulatory guides (which may be reproduced) or for placement on an automatic distribution list for single copies of future draft guides in specific divisions should be made in writing to the U.S. Nuclear Regulatory Commission, Washington, DC 20555, Attention: Reproduction and Distribution Services Section, or by fax to (301)415-2289; email <DISTRIBUTION@NRC.GOV>. Copies are available for inspection or copying for a fee from the NRC Public Document Room at 11555 Rockville Pike (first floor),

Rockville, MD; the PDRs mailing address is USNRC PDR, Washington, DC 20555; telephone (301)415-4737 or 1-(800)397-4209; fax (301)415-3548; e-mail <PDR@NRC.GOV>.

45 REFERENCES 1473 D.1 Electric Power Research Institute, "Seismic Hazard Methodology for the Central and 1474 Eastern United States," EPRI NP-4726, All Volumes, 1988 through 1991.

1475 D.2 Senior Seismic Hazard Analysis Committee (SSHAC), "Recommendations for 1476 Probabilistic Seismic Hazard Analysis: Guidance on Uncertainty and Use of Experts,"

1477 NUREG/CR-6372, USNRC, 1997.1 1478 D.3 K.L. Hanson et al., Techniques for Identifying Faults and Determining Their Origins, 1479 NUREG/CR-5503, USNRC,11999.

1480 D.4 International Atomic Energy Agency, "Earthquakes and Associated Topics in Relation to 1481 Nuclear Power Plant Siting," Safety Series No. 50-SG-S1, Revision 1, 1991.

1482 D.5 USNRC, Site Investigations for Foundation of Nuclear Power Plants, Regulatory Guide 1483 1.132, March 1979.2 (Proposed Revision 2, DG-1101, was issued for public comment in 1484 February 2001.)

1485 D.6 N. Torres et al.,Field Investigations for Foundations of Nuclear Power Facilities, 1486 NUREG/CR-5738, USNRC, 1999.1 1487 D.7 J.M. Sowers et al., Dating and Earthquakes: Review of Quaternary Geochronology and 1488 Its Application to Paleoseismology, NUREG/CR-5562, USNRC, 1998..1 1489 D.8 American Society of Testing and Materials, Standard Test Method for the Determination 1490 of the Modulus and Damping Properties of Soils Using the Cyclic Triaxial Apparatus, D 1491 3999, 1991.

1492 D.9 American Society of Testing and Materials, Standard Test Methods for Modulus and 1493 Damping of Soils by the Resonant-Column Method, D 4015, 2000.

1494 D.10 American Society of Testing and Materials, Standard Test Method for Load-Controlled 1495 Cyclic Triaxial Strength of Soil, D 5311, 1996.

1496 D.11 USNRC, Procedures and Criteria for Assessing Seismic Soil Liquefaction at Nuclear 1497 Power Plant Sites, Draft Regulatory Guide DG-1105, issued for public comment March 1498 2001.

1499 1500

46 D.12 H.B. Seed and I.M. Idriss, Ground Motions and Soil Liquefaction during Earthquakes, 1501 Earthquake Engineering Research Institute, Oakland, California, Monograph Series, 1502 1982.

1503 D.13 H.B. Seed et al., Influence of SPT Procedures in Soil Liquefaction Resistance 1504 Evaluation, Journal of the Geotechnical Engineering Division, ASCE, 111, GT12, 1225-1505 1273, 1985.

1506 D.14 A.W. Hatheway and C.R. McClure, Geology in the Siting of Nuclear Power Plants, 1507 Reviews in Engineering Geology, Geological Society of America, Volume IV, 1979.

1508 D.15 S. M. Colman, K. L. Pierce, and P.W. Birkland, Suggested Terminology for Quaternary 1509 Dating Methods, Quaternary Research, Volume 288, pp. 314-319, 1987.

1510

47 APPENDIX E 1511 PROCEDURE FOR THE EVALUATION OF NEW GEOSCIENCES INFORMATION OBTAINED 1512 FROM THE SITE-SPECIFIC INVESTIGATIONS 1513 E.1 INTRODUCTION 1514 This appendix provides methods acceptable to the NRC staff for assessing the impact of 1515 new information obtained during site-specific investigations on the data base used for the 1516 probabilistic seismic hazard analyses (PSHA).

1517 Regulatory Position 4 in this guide describes acceptable PSHAs that were developed by 1518 the Lawrence Livermore National Laboratory (LLNL) and the Electric Power Research Institute 1519 (EPRI) to characterize the seismic hazard for nuclear power plants and to develop the Safe 1520 Shutdown Earthquake (SSE). The procedure to determine the design earthquake ground motion 1521 (DE) outlined in this guide relies primarily on either the LLNL or EPRI PSHA results for the 1522 Central and Eastern United States (CEUS).

1523 It is necessary to evaluate the geological, seismological, and geophysical data obtained 1524 from the site-specific investigations to demonstrate that these data are consistent with the PSHA 1525 data bases of these two methodologies. If new information identified by the site-specific 1526 investigations would result in a significant increase in the hazard estimate for a site, and this new 1527 information is validated by a strong technical basis, the PSHA may have to be modified to 1528 incorporate the new technical information. Using sensitivity studies, it may also be possible to 1529 justify a lower hazard estimate with an exceptionally strong technical basis. However, it is 1530 expected that large uncertainties in estimating seismic hazard in the CEUS will continue to exist 1531 in the future, and substantial delays in the licensing process will result from trying to justify a 1532 lower value with respect to a specific site.

1533 In general, major recomputations of the LLNL and EPRI data base are planned 1534 periodically (approximately every 10 years), or when there is an important new finding or 1535 occurrence. The overall revision of the data base will also require a reexamination of the 1536 reference probability discussed in Appendix B.

1537 E.2 POSSIBLE SOURCES OF NEW INFORMATION THAT COULD AFFECT THE SSE 1538 Types of new data that could affect the PSHA results can be put in three general 1539 categories: seismic sources, earthquake recurrence models or rates of deformation, and ground 1540 motion models.

1541 E.2.1 Seismic Sources 1542 There are several possible sources of new information from the site-specific investigations 1543 that could affect the seismic hazard. Continued recording of small earthquakes, including 1544 microearthquakes, may indicate the presence of a localized seismic source. Paleoseismic 1545 evidence, such as paleoliquefaction features or displaced Quaternary strata, may indicate the 1546 presence of a previously unknown tectonic structure or a larger amount of activity on a known 1547 structure than was previously considered. Geophysical studies (aeromagnetic, gravity, and 1548 seismic reflection/refraction) may identify crustal structures that suggest the presence of 1549 previously unknown seismic sources. In situ stress measurements and the mapping of tectonic 1550 structures in the future may indicate potential seismic sources.

1551

48 Detailed local site investigations often reveal faults or other tectonic structures that were 1552 unknown, or reveal additional characteristics of known tectonic structures. Generally, based on 1553 past licensing experience in the CEUS, the discovery of such features will not require a 1554 modification of the seismic sources provided in the LLNL and EPRI studies. However, initial 1555 evidence regarding a newly discovered tectonic structure in the CEUS is often equivocal with 1556 respect to activity, and additional detailed investigations are required. By means of these detailed 1557 investigations, and based on past licensing activities, previously unidentified tectonic structures 1558 can usually be shown to be inactive or otherwise insignificant to the seismic design basis of the 1559 facility, and a modification of the seismic sources provided by the LLNL and EPRI studies will not 1560 be required. On the other hand, if the newly discovered features are relatively young, possibly 1561 associated with earthquakes that were large and could impact the hazard for the proposed 1562 facility, a modification may be required.

1563 Of particular concern is the possible existence of previously unknown, potentially active 1564 tectonic structures that could have moderately sized, but potentially damaging, near-field 1565 earthquakes or could cause surface displacement. Also of concern is the presence of structures 1566 that could generate larger earthquakes within the region than previously estimated.

1567 Investigations to determine whether there is a possibility for permanent ground 1568 displacement are especially important in view of the provision to allow for a combined licensing 1569 procedure under 10 CFR Part 52 as an alternative to the two-step procedure of the past 1570 (Construction Permit and Operating License). In the past at numerous nuclear power plant sites, 1571 potentially significant faults were identified when excavations were made during the construction 1572 phase prior to the issuance of an operating license, and extensive additional investigations of 1573 those faults had to be carried out to properly characterize them.

1574 E.2.2 Earthquake Recurrence Models 1575 There are three elements of the source zones recurrence models that could be affected 1576 by new site-specific data: (1) the rate of occurrence of earthquakes, (2) their maximum 1577 magnitude, and (3) the form of the recurrence model (e.g.,a change from truncated exponential 1578 to a characteristic earthquake model). Among the new site-specific information that is most likely 1579 to have a significant impact on the hazard is the discovery of paleoseismic evidence such as 1580 extensive soil liquefaction features, which would indicate with reasonable confidence that much 1581 larger estimates of the maximum earthquake than those predicted by the previous studies would 1582 ensue. The paleoseismic data could also be significant even if the maximum magnitudes of the 1583 previous studies are consistent with the paleo-earthquakes if there are sufficient data to develop 1584 return period estimates significantly shorter than those previously used in the probabilistic 1585 analysis. The paleoseismic data could also indicate that a characteristic earthquake model would 1586 be more applicable than a truncated exponential model.

1587 In the future, expanded earthquake catalogs will become available that will differ from the 1588 catalogs used by the previous studies. Generally, these new catalogues have been shown to 1589 have only minor impacts on estimates of the parameters of the recurrence models. Cases that 1590 might be significant include the discovery of records that indicate earthquakes in a region that 1591 had no seismic activity in the previous catalogs, the occurrence of an earthquake larger than the 1592 largest historic earthquakes, re-evaluating the largest historic earthquake to a significantly larger 1593 magnitude, or the occurrence of one or more moderate to large earthquakes (magnitude 5.0 or 1594 greater) in the CEUS.

1595

49 Geodetic measurements, particularly satellite-based networks, may provide data and 1596 interpretations of rates and styles of deformation in the CEUS that can have implications for 1597 earthquake recurrence. New hypotheses regarding present-day tectonics based on new data or 1598 reinterpretation of old data may be developed that were not considered or given high weight in 1599 the EPRI or LLNL PSHA. Any of these cases could have an impact on the estimated maximum 1600 earthquake if the result is larger than the values provided by LLNL and EPRI.

1601 E.2.3 Ground Motion Attenuation Models 1602 Alternative ground motion attenuation models may be used to determine the site-specific 1603 spectral shape as discussed in Regulatory Position 4 and Appendix F of this regulatory guide. If 1604 the ground motion models used are a major departure from the original models used in the 1605 hazard analysis and are likely to have impacts on the hazard results of many sites, a re-1606 evaluation of the reference probability may be needed. Otherwise, a periodic (e.g., every 10 1607 years) reexamination of the PSHA and the associated data base is considered appropriate to 1608 incorporate new understanding regarding ground motion attenuation models.

1609 E.3 PROCEDURE AND EVALUATION 1610 The EPRI and LLNL studies provide a wide range of interpretations of the possible 1611 seismic sources for most regions of the CEUS, as well as a wide range of interpretations for all 1612 the key parameters of the seismic hazard model. The first step in comparing the new information 1613 with those interpretations is determining whether the new information is consistent with the 1614 following LLNL and EPRI parameters: (1) the range of seismogenic sources as interpreted by the 1615 seismicity experts or teams involved in the study, (2) the range of seismicity rates for the region 1616 around the site as interpreted by the seismicity experts or teams involved in the studies, and (3) 1617 the range of maximum magnitudes determined by the seismicity experts or teams. The new 1618 information is considered not significant and no further evaluation is needed if it is consistent with 1619 the assumptions used in the PSHA, no additional alternative seismic sources or seismic 1620 parameters are needed, or it supports maintaining or decreasing the site mean seismic hazard.

1621 An example is a new ISFSI co-located near an existing nuclear power plant site that was 1622 recently investigated by state-of-the-art geosciences techniques and evaluated by current hazard 1623 methodologies. Detailed geological, seismological, and geophysical site-specific investigations 1624 would be required to update existing information regarding the new site, but it is very unlikely that 1625 significant new information would be found that would invalidate the previous PSHA.

1626 On the other hand, after evaluating the results of the site-specific investigations, if there is 1627 still uncertainty about whether the new information will affect the estimated hazard, it will be 1628 necessary to evaluate the potential impact of the new data and interpretations on the mean of the 1629 range of the input parameters. Such new information may indicate the addition of a new seismic 1630 source, a change in the rate of activity, a change in the spatial patterns of seismicity, an increase 1631 in the rate of deformation, or the observation of a relationship between tectonic structures and 1632 current seismicity. The new findings should be assessed by comparing them with the specific 1633 input of each expert or team that participated in the PSHA. Regarding a new source, for 1634 example, the specific seismic source characterizations for each expert or team (such as tectonic 1635 feature being modeled, source geometry, probability of being active, maximum earthquake 1636 magnitude, or occurrence rates) should be assessed in the context of the significant new data 1637 and interpretations.

1638

50 It is expected that the new information will be within the range of interpretations in the 1639 existing data base, and the data will not result in an increase in overall seismicity rate or increase 1640 in the range of maximum earthquakes to be used in the probabilistic analysis. It can then be 1641 concluded that the current LLNL or EPRI results apply. It is possible that the new data may 1642 necessitate a change in some parameter. In this case, appropriate sensitivity analyses should be 1643 performed to determine whether the new site-specific data could affect the ground motion 1644 estimates at the reference probability level.

1645 An example is a consideration of the seismic hazard near the Wabash River Valley (Ref.

1646 E.1). Geological evidence found recently within the Wabash River Valley and several of its 1647 tributaries indicated that an earthquake much larger than any historic event had occurred several 1648 thousand years ago in the vicinity of Vincennes, Indiana. A review of the inputs by the experts 1649 and teams involved in the LLNL and EPRI PSHAs revealed that many of them had made 1650 allowance for this possibility in their tectonic models by assuming the extension of the New 1651 Madrid Seismic Zone northward into the Wabash Valley. Several experts had given strong 1652 weight to the relatively high seismicity of the area, including the number of magnitude five historic 1653 earthquakes that have occurred, and thus had assumed the larger event. This analysis of the 1654 source characterizations of the experts and teams resulted in the conclusion by the analysts that 1655 a new PSHA would not be necessary for this region because an event similar to the prehistoric 1656 earthquake had been considered in the existing PSHAs.

1657 A third step would be required if the site-specific geosciences investigations revealed 1658 significant new information that would substantially affect the estimated hazard. Modification of 1659 the seismic sources would more than likely be required if the results of the detailed local and 1660 regional site investigations indicate that a previously unknown seismic source is identified in the 1661 vicinity of the site. A hypothetical example would be the recognition of geological evidence of 1662 recent activity on a fault near a site in the SCR similar to the evidence found on the Meers Fault 1663 in Oklahoma (Ref. E.2). If such a source is identified, the same approach used in the active 1664 tectonic regions of the WUS should be used to assess the largest earthquake expected and the 1665 rate of activity. If the resulting maximum earthquake and the rate of activity are higher than those 1666 provided by the LLNL or EPRI experts or teams regarding seismic sources within the region in 1667 which this newly discovered tectonic source is located, it may be necessary to modify the existing 1668 interpretations by introducing the new seismic source and developing modified seismic hazard 1669 estimates for the site. The same would be true if the current ground motion models are a major 1670 departure from the original models. These occurrences would likely require performing a new 1671 PSHA using the updated data base, and may require determining the appropriate reference 1672 probability.

1673 1674

1 Copies are available for inspection or copying for a fee from the NRC Public Document Room (PDR) at 11555 Rockville Pike, Rockville, MD; the PDRs mailing address is USNRC PDR, Washington, DC 20555; telephone (301)415-4737 or (800)397-4205; fax (301)415-3548; email <PDR@NRC.GOV>.

2 Copies are available at current rates from the U.S. Government Printing Office, P.O. Box 37082, Washington, DC 20402-9328 (telephone (202)512-1800); or from the National Technical Information Service by writing NTIS at 5285 Port Royal Road, Springfield, VA 22161; (telephone (703)487-4650; <http://www.ntis.gov/ordernow>.

Copies are available for inspection or copying for a fee from the NRC Public Document Room at 11555 Rockville Pike, Rockville, MD; the PDRs mailing address is USNRC PDR, Washington, DC 20555; telephone (301)415-4737 or (800)397-4209; fax (301)415-3548; email is PDR@NRC.GOV.

51 REFERENCES 1675 E.1 Memorandum from A. Murphy, NRC, to L. Shao, NRC,

Subject:

Summary of a Public 1676 Meeting on the Revision of Appendix A, "Seismic and Geologic Siting Criteria for Nuclear 1677 Power Plants," to 10 CFR Part 100; Enclosure (Viewgraphs): NUMARC, "Development 1678 and Demonstration of Industrys Integrated Seismic Siting Decision Process," February 1679 23, 1993.1 1680 E.2 A.R. Ramelli, D.B. Slemmons, and S.J. Brocoum, "The Meers Fault: Tectonic Activity in 1681 Southwestern Oklahoma," NUREG/CR-4852, USNRC, March 1987.2 1682

52 APPENDIX F 1683 PROCEDURE TO DETERMINE THE DESIGN EARTHQUAKE GROUND MOTION 1684 F.1 INTRODUCTION 1685 This appendix elaborates on Step 4 of Regulatory Position 4 of this guide, which 1686 describes an acceptable procedure to determine the design earthquake ground motion (DE). The 1687 DE is defined in terms of the horizontal and vertical free-field ground motion response spectra at 1688 the free ground surface. It is developed with consideration of local site effects and site seismic 1689 wave transmission effects. The DE response spectrum can be determined by scaling a site-1690 specific spectral shape determined for the controlling earthquakes or by scaling a standard 1691 broad-band spectral shape to envelope the ground motion levels for 1 Hz (Sa,1) and 10 Hz (Sa,10),

1692 as determined in Step C.2-2 of Appendix C to this guide. The standard response spectrum is 1693 generally specified at 5 percent critical damping.

1694 It is anticipated that a regulatory guide will be developed that provides guidance on 1695 assessing site-specific effects and determining smooth design response spectra, taking into 1696 account recent developments in ground motion modeling and site amplification studies (for 1697 example, Ref. F.1).

1698 F.2 DISCUSSION 1699 For engineering purposes, it is essential that the design ground motion response 1700 spectrum be a broad-band smooth response spectrum with adequate energy in the frequencies 1701 of interest. In the past, it was general practice to select a standard broad-band spectrum, such 1702 as the spectrum in Regulatory Guide 1.60 (Ref. F.2), and scale it by a peak ground motion 1703 parameter [usually peak ground acceleration (PGA)], which is derived based on the size of the 1704 controlling earthquake. Past practices to define the DE are still valid and, based on this 1705 consideration, the following three possible situations are depicted in Figures F.1 to F.3.

1706 Figure F.1 depicts a situation in which a site is to be used for a certified ISFSI or MRS 1707 design (if available) with an established DE. In this example, the certified design DE spectrum 1708 compares favorably with the site-specific response spectra determined in Step 2 or 3 of 1709 Regulatory Position 4.

1710 Figure F.2 depicts a situation in which a standard broad-band shape is selected and its 1711 amplitude is scaled so that the design DE envelopes the site-specific spectra.

1712 Figure F.3 depicts a situation in which a specific smooth shape for the design DE 1713 spectrum is developed to envelope the site-specific spectra. In this case, it is particularly 1714 important to be sure that the DE contains adequate energy in the frequency range of engineering 1715 interest and is sufficiently broad-band.

1716

53 (Note: The above figures 1717 illustrate situations for a rock site.

1718 For other site conditions, the DE spectra are compared at free-field after performing site amplification studies 1719 as discussed in Step 3 of Regulatory Position 4.)

1720

1 Copies are available at current rates from the U.S. Government Printing Office, P.O. Box 37082, Washington, DC 20402-9328 (telephone (202)512-1800); or from the National Technical Information Service by writing NTIS at 5285 Port Royal Road, Springfield, VA 22161; (telephone (703)487-4650; <http://www.ntis.gov/ordernow>. Copies are available for inspection or copying for a fee from the NRC Public Document Room at 11555 Rockville Pike, Rockville, MD; the PDRs mailing address is USNRC PDR, Washington, DC 20555; telephone (301)415-4737 or (800)397-4209; fax (301)415-3548; email is PDR@NRC.GOV.

2 Requests for single copies of draft or active regulatory guides (which may be reproduced) or for placement on an automatic distribution list for single copies of future draft guides in specific divisions should be made in writing to the U.S. Nuclear Regulatory Commission, Washington, DC 20555, Attention: Reproduction and Distribution Services Section, or by fax to (301)415-2289; email <DISTRIBUTION@NRC.GOV>. Copies are available for inspection or copying for a fee from the NRC Public Document Room at 11555 Rockville Pike (first floor),

Rockville, MD; the PDRs mailing address is USNRC PDR, Washington, DC 20555; telephone (301)415-4737 or 1-(800)397-4209; fax (301)415-3548; e-mail <PDR@NRC.GOV>.

54 REFERENCES 1721 F.1 R.K. McGuire, W.J. Silva, and C.J. Constantino, Technical Basis for Revision of 1722 Regulatory Guidance on Design Ground Motions: Hazard-and Risk-Consistent 1723 Ground Motion Sp[ectra Guidelines, NUREG/CR-6728, 2001.1 1724 F.2 U.S. NRC, Design Response Spectra for Seismic Design of Nuclear Power Plants, 1725 Regulatory Guide 1.60, Revision 1, December 1973.2 1726

55 REGULATORY ANALYSIS 1727 A separate regulatory analysis was not prepared for this draft regulatory guide. The 1728 regulatory analysis Regulatory Analysis of Geological and Seismological Characteristics for 1729 and Design of Dry Cask Independent Spent Fuel Storage Installations (10 CFR Part 72), was 1730 prepared for the amendments, and it provides the regulatory basis for this guide and examines 1731 the costs and benefits of the rule as implemented by the guide. A copy of the regulatory 1732 analysis is available for inspection and copying for a fee at the NRC Public Document Room, 1733 as Attachment 3 to SECY-02-0043. The PDRs mailing address is USNRC PDR, Washington, 1734 DC 20555; telephone (301)415-4737 or 1-(800)397-4209; fax (301)415-3548; e-mail 1735

<PDR@NRC.GOV>.

1736