ML20197H997
| ML20197H997 | |
| Person / Time | |
|---|---|
| Site: | 05000000, Diablo Canyon |
| Issue date: | 03/31/1977 |
| From: | Gossick L NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO) |
| To: | Udall M HOUSE OF REP. |
| Shared Package | |
| ML20197J003 | List: |
| References | |
| FOIA-86-371 NUDOCS 8408210267 | |
| Download: ML20197H997 (38) | |
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4 HAR 31197I fae inacracle rerris K. odall, Chairman -
Subcomittee on Energy and the Environment Cecraittee on Interior anMncular Affairs United States flouse of Ibpresentatives Washington, D. C. 20515
Dear Mr. Chair..un:
I am pleased to respond to your letter of February 9,1977 to Chairman Iowden. You requested certain information regarding the earthquake hazard at the Diablo Canyon Nuclear Generating Station presently under construction in California. This case is under consideration by an Atcalc Safety ard Licensing i30ard. Since any decision or ruling oy tne licensing board is subject to review by tne Cosimission, it would not to appropriate for tne Coc;nissioners to coscent on the details at this tirc.e. Accordingly, your letter was referred to ae for reply.
Our answra are containeo in Enclosure 1 to tnis letter ana are nu oered to correspond to your questions, faclosures 2 and 3 contain a brief sunnary and a chronology, respectively, of the M:C/NRC safety reviews which may be useful in reading the answers. The remaining enclosures contain certain information referenced in the answers. I trust you will W.
find the enclosed information responsive to your request.
Sincerely, IIIsited) Lee V. Cossact Ice V. Gossick D(ecutive Director for Operations
Enclosures:
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The Honoraole iaorris d.. Quall-' inclosures:
- 1. - Fesponses to Questions 2.
Suanary or diC Safety myiew Status for the Diablo Canyon liuclear Power Plant, Units 1 and-2 3.
Cnronology of Priricipal Events in tne AeT/Nic Safety F.eviews of t.%
Diaolo Canyon Nuclear Power Plant, Units 1 ani 2 4.
Section II of Appendix 2.50 to Araend:rment 19 to FSAft cated Octot-tr 30, 1974 5.
AEC i<egulatory Staff's Suppleraental Proposec Findins3s of Fact aru Conclusions of 12N, dated Septer.tcr 30, 1970 6.
Initial Cecision of the Atoinic safety anc I.icensing Soara, for 01:wlo Canyon Unit 2, Decemoer 8,1970 7.
Mport for California EtJC Decision tio. 73278, Diablo Canyon, Unit 1, dated nove:;cer 7,1967 6.
P.cport Ior California FUC Decision flo. 75471, Diaolo Canyoa, Unit 2,
-dated narch 25, 1969 9.
Final Dwiron. ental Statement, May 1973
- 10. Su;pler.cnt ;io. 4 to the Safety Evaluation Report dated day 11,197o
- 11. Qualifications of Dr. Natnan tJewnark M
- 12. Qualifications of Dr. Williara Hall
- 13. Geolajical Survey Circular 672, 1972 14.
Sopploraent No. 5 to the Safoty Evaluation Peport dated Septemoer 10, 1976 15.
rworamua cated novecoer 24, 1976 enclosin; staff report to AC:!J 16.
IErz standard 344-1971
- 17. :.catingnouse P.e, cort WCA?-7920, Septe::bcr 1972 18.
IE88 Standard 344-1975
- 19. GtC Legu12 tory Gilde 1.100, tiarcn 1976
- 20. NTC Ictter from the Director of Nuclear Feactor Pegulation to tno Chaircan of the California Energy Resources Conservation and OcVelograent Coramission, dated tiarch 18, 1977 r
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ENCLOSURE NO. 1 RESPOTSES TO QUESTIONS 5eXsu e
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3 ENCIOSURE 1
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Pre-construction: Prior to 1970:
I.1 QUESTION To what extent did the AEC or applicant conduct any offshore surveys before construction licenses were granted?
RESPONSE
he Construction Permits were issued in April 1968 and December 1970 for Units 1 and 2, respectively.
No offshore surveys were conducted by PG&E before the_ construction permits were issued.
The AEC's advisor, the U. S. Geological Survey (USGS), has informed wggge us that, in 1970, specifically for the Diablo Canyon review, four existing traverse lines that crossed the area of interest were examined. These traverse lines were from sparker surveys that had previously-been performed in 1968 by G. A. Rusnak on the USGS ship R. V. Polaris as part of a broader regional study. 'Ihey were examined in 1970 to evaluate an intervenor's contention about offshore earth-quake epicenters.
(See the response to question I.S.)
%e traverse lines did not support the intervenor's contention. They did show a belt of disturbed and faulted strata that later came to be known as the Ilosgri fault zone. However, sin'ce these traverse lines did not show any dislocation or faulting at the ocean floor (but' rather at depth), there was no evidence at that time to suggest i
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. possible capability of the zone, a determination of which subsequent more extensive surveys supported.
(See the response to question III.1 for further discussion of this subject.)
In addition, some general offshore surveys had been conducted in the central California region by various institutions prior to issuance of the construction permits. Such general surveys were sunmarized by PG&E in portions of Amendment 19 to the Final Safety Analysis Repor t ( PSAR).
(See Enclosure 4.)
I.2 QUCSTION Was the AEC staff aware of any responsible scientific opinion Ed4F' prior to ccTaencement of construction of the Diablo Canyon plants that held that seismic data on the central California coastal region was inadequate?
RESPONSC During the Unit 2 construction permit proceedings an intervenor (Scenic Shoreline Preservation Conference) raised questions about the adequacy of the seismic design basis. The Conference presented testimony from Mr. Ralph Vrana, an instructor in the Physics Dapartment of the California Polytechnic Institute.
Some of Mr. Vrana's views were subsequently published in riarch 1971 in the Geological Society of America Bulletin.
In addition, various letters from the Conference were presur, ably based, in part, on 'the advice _ of Dr. Robert Curry, an Assistant Professor of Geology at the University of California at Santa Barbara, who was one of the founders of the Conference.
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. 'Ihe Conference raised a number of questions, including gaestions about a possible line of offshore earthquake epicenters (See question I.5) and certain faults and seismic activity. These questions were evaluated by the staff, the USGS and the U. S. Coast and Geodetic Survey. These matters are saamarized in the staff's supplemental findings submitted to the Atomic Safety and Licensing Board on September 30,1970 (Enclosure 5).
The Conference also contended that additional survey work, including offshore surveys, should be performed. The Atomic Safety and Licensing Board discussed this contention in its decision and, in light of fMiiiik the conservatism in the design basis, concluded that the seismic design basis was adequate (See pages 21 and 22 of the initial decision for Diablo Canyon, Unit 2 dated December 8, 1970, Enclosure 6).
I.3 QUESTION Did the AEC staff review the California PUC record to determine if any questions were raised in PUC proceedings regarding offshore faulting? If the staff did review the record and found questions were raised regarding offshore faulting how did the staff respond?
RESPONSE
The AEC staff did not review full records of the California PUC proceedings, which are quite extensive, to determine exactly what questions about offshore faulting or other seismic concerns might have been raised.
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. ne California PUC decisions for Units 1 and 2, which include brief sumaries of the proceedings, have been in the AEC's files since the time of the construction permit reviews and were doubtless read by cognizant staff personnel at that time. The PUC decision for Unit 1,, indicates that there was opposition to the plant based on objections to transmission lines and a desire to preserve the natural state of the site, but mentions no opposition based on seismic concerns.
%e PUC decision for Unit 2, Enclosure 8, indicates that the Scenic Shoreline Preservation Conference moved for continuance to enable it to present, among other things, additional studies regarding the geology of the Diablo Canyon area. The motion was denied. The PUC decision iiiils does not go into any detail regarding the nature of the additional geologic studies proposed by the Scenic shoreline Preservation Conference.
Ilowever, the Scenic Shoreline Preservation Conference, as an intervenor in the AEC proceedings, raised seismic questions prior to the PUC decision on Unit 2 in March 1969, and continued to do so afterwards.
The last hearing was held in August 1970. These questions were, of course, evaluated by the AEC staff and its advisors.
(See the response to question I.2.)
I.4 QUESTION Did any geologists not directly affiliated with the AEC staff or applicant conduct surveys during the 1967-70 period that located the ilosgri fault?
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. RESPONSE Yes.
Ernest G. Hoskins and John R. Griffiths published a paper in January 1971, based on Shell Oil Company surveys, that revealed the existence of the Hosgri fault.
I.5 QUESTION During construction license proceedings (1968-70) was the AEC staff aware of a line of earthquake epicenters off the central California coast that traced a ti.7/SE trending line running within a few miles of the plant site?
RESEONSE The only such line of which the staff was or is aware trends in the NE/SW direction rather than the IM/SE direction.
Questions about this matter were raised by an intervenor during the Unit 2 construction permit proceedings. Some small offshore earthquakes which occurred in 1969 and 1970 gave the appearance of defining a NE/SW trending line that, if projected to the Northeast, would pass near the plant. The concern was that this might indicate an active fault that could pass near the plant. This question was evaluated by the staff, the USGS and the US Coast and Geodetic Survey.
It was concluded that the earthquake epicenters did not indicate such a fault and did not imply a hazard to the plant. These matters are summarized in the staff's supplemental findings subnitted to the Atomic Safety and Licensing Board on September 30, 1970 (Dnclosure 5).
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. Subsequent work has verified this finding.
In fact, subsequent relo-cation of the epicenters of these earthquakes has indicated that the epicenters do not form a line, but rather, they occurred in a cluster about the Santa Lucia Bank fault system.
I.6 QUESTION During construction license proceedings, was the AEC staff aware of any investigations by P.G.&E. for faults at other potential reactor sites? Did the AEC consider any such investigations adequate or inadequate?
RESPG1SE The AEC staff was not aware of the details of any preliminary investigation by PG&E for faults at other alternative reactor sites M
conaidered by PG&E in their process of celecting the Diablo Canyon site. At the time of the staff licensing review of the applications for construction permits for the Diablo Canyon units, there was no Commission requirement for the 1969 liational Environmental Policy Act (tJEPA) evaluation of alternatives including alternate sites as has been done for applications for construction permits since 1970.
(Also see response to question II.4.)
llowever, PG&E did consider eleven California coastal area sites and one inland site before selecting the present Diablo Canyon site. This is discussed in the California PVC decision for Unit 1 (Enclosure 7).
The PUC report does not indicate that seismic concerns were factors
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7-in the final site selection The staff's Final Environmental Statement subsequently issued in May 1973 (Enclosure 7) discussed alternative sites and concluded that the decision to select the Diablo Canyon site "is probably as acceptable by today's starxlards as any site that was considered in 1965 or earlier."
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Post-ground-breaking : 1970-1975:
II.1 QUESTION When did the AEC staff first become aware of the Hoskins-Griffiths paper reporting the existence of the Hosgri Fault?
RESPONSE
'Ihe AEC staff first became aware of the Hoskins and Griffiths paper in August 1973, while performing an acceptance review of the Diablo Canyon Final Safety Analysis Report (PSAR). The paper was mentioned
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in the PSAR and the AEC staff requested additional information about it.
(See the response to question III.1 for further discussion of this subject. )
M II.2 OUESTION 1l hen did AEC-ordered surveys designed to verify the Hoskins-Griffiths report begin?
RESlW SE PG&D began its surveys in December 1973 to answer the staff's questions.
In addition, t% USGS had been conducting general surveys of the area offshore from central and southern California since before the construction permits were issued. 'Itese were for the purpose of determining regional offshore geologic structure rather than to verify e
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, the faulting discussed in the lioskins and Griffiths paper. Some of these surveys were funded by the AEC. In the fall of 1973, as part of this program, the USGS began performing additional surveys in the area irnediately offshore from Diablo Canyon to provide a more refined picture of this area.
II.3 QUESTION What efforts did'the AEC staff make and at what times to evaluate the applicability to Diablo Canyon of seismic information gathered during the 1971 San Fernando Valley earthquake?
RESPONSE
The staff and the USGS have considered the applicability of this seismic information'to all reactor sites, including Diablo Canyon, since the San Fernando earthquake occurred.in 1971. The staff has.
never believed that San Fernando earthquake data warrant increasing the severity of the Diablo Canyon seismic design basis in relation to' the faults that originally. controlled the design.
Subsequently, when the effects of the nearby llosgri fault were con-sidered for Diablo Canyon, the San Fernando earthquake information comprised a significant part of the data used in evaluating the l
l riodified seismic design basis for Diablo Canyon. 'Ihis firs.t appeared in D2cember 1974 when the staff requested a reevaluation of t'he i
plant's design at 0.59 It was considered again in 1976 in.the USGS l
recorxaended ground motions and the staff's determination of an effective engineering accel.eration.
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- II.4 00csTION Did the AEC consider new information regarding earthquake hazards from the liosgri Fault at the 1973-74 environmental hearings?. If not, why not?
RESPONSE
1he AEC ~did not consider any seismic issues at the environmental hearings which were held for Diablo~ Canyon Unit 2 in 1973-74.
Those hearings were held pursuant to Section B of 10 CFR Part 50, Appendix D, in order to correct certain deficiencies in the environmental assessments of licenses issued after January 1, 1970 (the effective date of the National Environmental Policy Act)
'but prior to the decision by the Circuit Court for the' District of Columbia in the Calvert Cliffs' proceeding, 449 F.2d 1109 (D.C.
Cir. 1971). The sole purpose of those Section B environmental hearings was to determine, in the light of newly formulated-regu-lations occasioned by the Calvert-Cliffs' decision, whether environ-mental considerations required the continuation, modification, termination, or conditioning of the constr'uction permit for Diablo Canyon,. Unit 2 which was issued on December 9, 1970.
Itecause those hearings were considered ~ to be an extension of the environmental hearings upon which the Diablo Canyon construction
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permit was issued and the subject matter of those hearings was limited solely to environmental concerns (the Commission has traditionally, because of the length of hearings in contested cases, divided its proceedings into the subject areas of safety
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, and the environment) the Atomic Safety and Licensing Board declined to hear evidence on seismic issues. The Licensing Board ruled that seismic issues would be appropriate for hearing in the safety hearings connected with the then-pending application for an operating license which was docketed on October 2,1973.
II.5 QUESTIOl Did the AEC ever order work stoppages to allow for a full consid-eration of the potential earthqua:;e hazard f rom the Ilosgri Pault before work on the Diablo Canyon plant proceeded to completion?
RESP 0i4SE The Commission has never ordered work stoppages at Diablo Canyon
$bim because of seismic questions.
This question was considered most recently by the Atomic Safety and Licensing Board in ispril 1974 and November 1974 in response to requests by intervenors for stop work orders because of seismic issues. The Board decided that it was not necessary to make a separate, immediate decision on stopping work but rather, the adequacy of the seismic design would be considered at the forth-coming operating license hearings. The Board considered many factors and listed die following reasons, which focus on safety, as' among -the most important ones for taking this approach:
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Continued construction of the plant poses no risk to the health and safety of the public, regardless of any geologic problems which might exist. Operation of the plant is, of course, a quite different matter. The Board thus feels that consideration of seismic issues is properly carried out in the operating license procedure.
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Argument that the incremental cost of continued construction could have an effect upon the eventual granting of an operating license is, from a health and safety standpoint, invalid.
Economic factors cannot be considered in any matter which involves a risk to the puolic health and safety.
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Continued construction will neither conceal nor render inaccessible any of the geologic features of the site not already affected."
In addition, the IEC staff believed that there were and are no RiE66*
significant impacts on the natural environment from continuing construction as opposed to stopping construction.
Final]y, in these particular circumstances one would naturally ask if it were not prudent to stop expending money and material on construction until the seismic issues were resolved. The staf f considered this question. The potential savings (money that could be saved if the project must be abandoned) were outweighed by the potential costs (money that could be lost due to delay if the project were not abandoned).
In addition, the staff believed that there was reasonable assurance that.the seismic issue could eyentually.be resolved. Accordingly, the staff did not believe there'was a basis for stopping construction.
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III. Current situation:
III.1 QUESTION When did the Commission staff officially recognize the Hosgri Fault. as the most serious-potential earthquake hazard at Diablo Canyon?
RESPOW E The Commission staff first officially took action recognizing that the Hosgri fault would increase the seismic design basis in December 1974. This was in the form of a letter to PG&E requesting a reevaluation of the plant's seismic design at a level of 0.59 as compared to an original design level of 0.4g.
A short history of the principal milestones in the level of knowledge and. concern about the Hosgri fault is given below.
As was discussed in the response to question I.1, the USGS has informed us that surveys prior to issuance of the construction permits had shown a belt of faulted and disturbed strata. However, since the surveys did "not show any dislocation or faulting at the ocean floor, but rather at depth, there was no evidence at that time to suggest possible capability of the zone, a determination of which subsequent more extensive surveys supported.
As was discussed in the response-to. question II.1, in August.1973.
the AEC staff requested a'dditional'information about the faulting that had been discusst,d in the 1971 Hoskins and Griffiths paper.
At that time the purpose of the questions was simply to find out more about the subject. The fault was not known to be capable of O
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> generating earthquakes, much less great earthquakes.
Published seismic history indicated virtually no earthquakes offshore in the vicinity of the Hosgri fault.
In November 1973 the USGS reported that survey work in progress had shown a possible fault dislocation at the ocean floor offshore from Diablo Canyon. A fault dislocation at the ocean floor, rather than at depth, would indicate recent movement and a capability for generating earthquakes. The dislocation that was reported eventually turned out to be something else - a terrace rather than recent faulting.
Nevertheless, concern that the fault was capable of generating earth-quakes continued from that time and further survey work supported the N
judgement that the fault was capable.
In September 1974, af ter performing surveys, PGLE gave a presentation on the Hosgri f ault at an ACRS subcommittee meeting. By that time it was clear from the additional surveys that had then been parformed that the fault's capability for generating earthquakes could not be precluded.
In Daccaber 1974, after PG&B had responded to the staff's questions about the fault, the staff officially recognized that the Hosgri fault would increase the. seismic design basis and requested a reevaluation of the plant at 0.59 At that time, the staf f and USGS evaluation of the fault had not been completed and the new design basis was a preliminary estimate based on PG&E's assessment of the fault.
Little rean'alysis and few, if any, modifications would O
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. have been required to meet the new basis (0.5g) because of conserva-tisms in the original design.
In January 1975 a USGS evaluation was received which stated that, in light of current information, 0.5g was inadequate. The USGS raised questions about PG&E's interpretation of the fault's earthquake potential. There were questions about the length of the fault.
In addition, the staff learned at that time of a recent study by William Gawthrop that had indicated the 1927 earthquake, of magnitude 7.3, might have been on the Bosgri fault. The 1927 event had previously been located much further out to sea. The possibility of a magnitude 7.3 earthquake on the Hosgri fault greatly increased the level of
- %M*s concern about the severity of an earthquake that could occur at the site. She staff officially recognized the USGS evaluation and regaested additional information from PGSE to address the questions that had been raised.
In April 1976, after a review of the further information provided by PG&E and numerous discussions, another USGS evaluation was received.
In this evaluation, the previous conclusion was not changed but a specific assessment of the design basis earthquake was provided. This earthquake, which is discussed in the response to question III.5, was much more severe than the original design basis earthquakes. The NRC staff officially accepted this evaluation and requested an appropriate reevaluation of the plant on this basis.
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RESPONSE
The USGS and the Cocaission staff have considered this matter. The hypothesis is that at its northern end, the Hosgri fault may be linked with the San Simeon fault which, in turn, at its northern end, may be linked with the San Gregorio fault.
Datermining the length of the Hosgri fault has been a consideration
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throughout the operating licence review. Tne tJRC staff first specifically addressed this question in February 1975 when further information concerning the northern tarrination of the Hosgri fault was requested from PGLE. 'Ihis was after the USGS had provided an evaluation and had raised questions concerning PGSE's inter-pretations of the fault's northern termination.
The staf f has not requested further surveys because such work would not alter the conclusions about the maximum earthquake potential at this site. 7he most recent USGS evaluation discussed this matter at length. Essentially the USGS assumed that the links exist, but determined that "the Hosgri, San Simeon, and San Gregorio faults, even if parts of a copmon zone of deformation, have the dominant characteristics of subsidiary faults within the San Andreas system.
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. Such subsidiary faults have no record of or estimate of earthquakes larger than magnitude 7.5 on them." Accordingly, confirming the existence of the links would not increase the postulated magnitude.
On the other hand, refuting the existence of the links would not decrease the magnitude since the USGS also deterrained "that the 1927 earthquake could have occurred on the Ilosgri fault and that a similar earthquake with a it.agnitude of about 7.5 could occur in the future anywhere along the ilosgri fault."
(See Supplement No. 4 to the SCR, Enclosure 10).
III.3 CUSSTIO'1 Ilas the Commission staff hired any ottier outside consultants besides Dr. Nathan Newmark to assess the seire.ic hazards at Diablo Canyen? If so, please identify these consultants, their areas of expertise and the dates they were retained.
RESPONSE
The US Geological Survey has reviewed the Diablo Canyon operating license application in the areas of geology and seismology which encompass the basic assessment of the maximum earthquake potential for the site. fne survey has been involved in this capacity as an advisor to the imC staff throughout the operating license review of this project.
Dr. Nathan Newmark, and Dr. William IIall, who have long been con-sultants to the NRC staff, have been reviewing the Diablo Canyon operating license application in the area of seismic design since O
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Dr. Newmark is an expert in seismic design and structural dynamics. He is a Professor of Civil Engineering and in the Center for Advanced Study, Emeritus, University of Illinois at Urbana-Champaign. His qualifications are summarized in Unclosure 11.
Dr. Hall is an expert in engineering materials and earthquake engineering. He is a Professor of Civil Engineering at the University of Illinois at Urbana-Champaign. His qualifications are summarized in Enclosure 12.
In addition, Mr. D. L. Bernreuter and Dr. L. H. Wight, experts in structural mechanics and seismology at the University of California's Lawrence Livermore Laboratory, have been performing theoretical calculations concerning potential ground motions at the site for the staff since February 1976.
As you are probably aware, the Advisory Committee on Reactor Safeguards, which is indep6ndent qf the (1RC staff, has employed several outside consultants in its review to date of the seismic aspects of the Diablo Canyon operating license application. The principal ACRS consultants' names and areas of expertise, titles, and the dates they began their reviews of the Diablo Canyon opera. ting license application are listed below.
Dr. Benjamin Page, Geology (Professor of Geology, Department of
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Geology, Stanford University), February 1975.
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Dr. Shaler Philbrick, Geology (Professor of Geological Science, Retired, Cornell University), September 1974.
Dr. George Thompson, Geophysics (Professor and Department Chairman, Department of Geophysics, Stanford University), September 1974.
Dr. James Wilson, Geophysics & Seismology (Director, Institute-of Science and Technology, University of Michigan), February 1975.
Dr. Mihailio Trifunac, Seismology (Associate Professor of Civil Engineering, University of Southern California), September 1974.
Dr. Merit White, Seismic Design (Commonwealth Professor and Head, Civil Engineering Dapartment, University of Massachusetts, February 1975.
Dr. _ R. J. Scavazzo, Structural Mechanics (Professor and Head of Department, Department of Mechanical Engineering, University of Akron), October 1976.
Dr. Thomas Pickel, Seismic Design (Department-Manager, Engineering Analysis Department, Oak Ridge National Laboratory), May 1976.
Dr. Morris Reich, Structural Mechanics (llead of Structural Analysis.
Group, Department of Applied Science,.Brookhaven Nat'ional Laboratory),
August 1976.
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. Dr. Enrique Luco, Seismology & Structural Mechanics ( Assistant Professor of Applied Mechanics, University of California at San Diego), October 1976.
III.4 QUESTION Has the Commission staff placed seismic stations in the field on the coast to measure seismic activity along the Hosgri? If so, are these stations still in place taking measurements?
RESP 3;SE Existing permanent seismic stations would be capable of detecting and locating large earthquakes that might occur on the Hosgri fault.
Proparly placed fielo instruments would be necessary to detect and lisliiW9 locate small carthquakes that might occur on the Hosgri fault. To the imC staff's knowledge, the only such fielo instruments that have been employed were op2ratcJ for about 6 months in the spring and sumaer of 1973 by the USGS.
The NRC staff and the -USGS do not believe that the op3 ration of such instruments in that area would be of significant help in assessing the adequacy of the seismic design basis for Diablo Canyon.
They could not define with any certainty the probability of a large earthquake occurring on the fault. They could shed a limited a:aount of light' on the nature of the fault and the frequency of small earth-quakes in the area of the fault. Such information would not, however, change the evaluation of the maximum earthquake potential at the 9
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site since this evaluation is' based primarily upon the following two determinations which are given in the most recent USGS evaluation:
(1) "that the 1927 earthquake could have occurred on the Hosgri fault and that a similar carthquake with a magnitude of about 7.5 could occur in the future anywhere along the Hosgri fault."
(2) that "the Hosgri, San Simeon, and San Gregorio faults, even if parts of a common zone of deformation, have the dominant charac-teristics of subsidiary faults within the San Andreas system.
Such subsidiary' faults have no record of or estimate of earth-quakes larger than magnitude 7.5 on them."
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No. 4 to the SER, Cnclosure 10).
III.5 09ESTION It has been. suggested that the following parameters would be characteristic of an earthquake that might occur during the Diablo Canyon plants' lifetimes:
Distance of epicenter from plant site: -10 kms.
-Magnitude: 7.9 Richter Acceleration: 1.1 g-Itaximum velocity:- 50" per second Displacement: 36" Duration: 40-60 seconds at 5% of maximum acceleration Frequencies of 4 hertz Damping: 2%
Assuming ' he present plant design, would its structure', systems, t
s and co;nponents important to safety be able to withstand the effects of an earthquake characterized by the parameters listed above?
If not, what safety related plant co;nponents are nast likely not to withstand an earthquake with the above parameters?
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. Is the staff using parameters of at least the above magnitude in its seismic safety analyses for Diablo Canyon?
If not, what was the rationale for celecting other parameters?
RESPONSE
(1) Suggested earthquake
%e parameters listed above do not correspand to any sugges-tion that has been made to the NRC staff. Tney do recemble, with some exceptions, the ground motion parameters provided by the USGS. The response will be in relation to the USGS values.
The USGS recommendation represents an assessment of the Edilisy maximum earthquake potential of the site which is much more severe than an earthquake that is likely to occur during the plants' lifetime.
The USGS ground motion values characterize free field ground motion as might be recorded on an cccelerogram at the ground surface. %ey contain no factors related to the nature of structures. These numbers are, therefore, quite clearly not intended to be useJ directly for design along with the NRC seismic design criteria, but rather "should be used in the
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derivation of an effcctive engineering acceleration for input into the process leading to the seismic' design analysis."
(See the USGS reoort in Supplement No. 4 to the SER, Enclosure 10, and Geological Survey Circular 672, Enclosure 13.)
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. 'Ihe USGS ground motion values may be briefly summarized as follows:
Distance: This approach is appropriate for sites within 10 km of a causative fault Magnitude: 7.5 Richter Acceleratioa: 1.159 first peak 1.00g second peak 0.85g fifd1 peak 0.65g tenth peak velocity: 135 ca/sec (53 in/sec) first peak 115 cm/sec (45 in/sec) second peak 100 cm/sec (39 in/sec) third peak Displacement: 70 cm (23 in)
Duration:
40 sec exceeding 0.05g Frequencies: Not specified Damping: Not sp2cified (a property of the structure being designed)
The complete recommendation is provided in Enclosures 9 69er and 13.
(2)
Response of the olant PGLE is performing a reanalysis of the plant to determine what 1,yx3ifications may be needed to safely withstand the earthquake.
Since the results of the reanalysis are not yet available, the staf f cannot say whether, assuming the present plant design, the safety related parts of the plant could withstand the suggested earthquake discussed above.
It seems likely to the staff that the reanalysis will indicate that some of the safety related parts of the plant will need modification to provide an acceptable margin of safety for a full term operating license for die life of the plant.
v
)
. Until the reanalysis is performed the staff can only speculate that the items susaarized below are likely to be candidates for modification to assure that they will withstand load combinations, including the design basis earthquake, within acceptable criteria.
(a) liith regard to structures, it is our understanding that the highly stressed portions could be:
(i) the uppermost parts of the auxiliary building and turbine buildings, which are made of steel framing rather than reinforced concrete; and (ii) a curtain wall on the ocean side of the intake structure.
(b) liith regard to the systems and components inside the structures, the staff currently has no estimates as to what items are likely to need modification.
(3)
Parameters used by the staff (a) USGS ground r.otion values The staff has approved, for use in the reanalysis, para-meters that are considered to be consistent with the USGS ground motion values given above. The design numbers are not the same as the USGS numbers because the USGS nur.bers are free field ground motion values, which do not reflect design considerations of structural response and are not
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- intended to be used directly in design.
Rather, they are intended to be used in deriving an effective engineering acceleration for use in design.
Very briefly, there are two principal reasons for differ-ences between the effective engineering acceleration and the highest peak acceleration of the free field ground motion.
In the first case, as it is used in design calculations, the effective engineering acceleration represents a Icvel of shaking that is repeated a sufficient number of times that the structures achieve a high level of calculated W
response. A peak that is not repeated in this manner would cause a lower structural response. In the second case, large structures do not respond as fully to high frequency ground motions as do small structures or small instruments. Some credit has been allowed for this phenomenon.
With regard to velocity, data indicate that peak velocities in rock are considerably lower than peak velocities in soil for the same acceleration. Since Diablo Canyon is a rock site, this was considered in selecting a velocity value.
These matters are discussed more fully in Appendix C to Supplement No. S to the-SER (Enclosure 14) and a staff report provided to the ACRS in November 1976 (Enclosure 15).
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)
- 'Ihe effective acceleration and other criteria approved by the staff for use in the reanalysis are currently. undergoing a full review by the ACRS and its consultants. The ACRS consultants have provided a wide range of coments and questions on the subject. PG&E and the NRC staff are currently considering the consultants' coments and questions and will respond to them in the near future.
(b) DaTping Damping is a property of the structure or system being excited by earthquake motion rather than of the earthquake.
iiiTEM itself.
It varies as a function of material and configuration.
Accordingly, the USGS values do not include a recommendation on damping.
Damping is an important parameter. Smaller assumed damping values will give larger calculated responses in the plant.
However, large responses that induce high stresses in the plant will develop correspondingly larger damping values that tend to limit the responses.
The NRC staff's criteria for performing the. reanalysis include acceptance of tlie ~use of the da aping values listed in the NRC's Regulatory Guide 1.61, " Damping Values for Seismic Design of Nuclear Power Plants", rather than the ver y conservative values that had been used in the original analysis. The
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- Regulatory Guide 1.61 values have been acceptable for new plant applications since the Regulatory Guide was issued in 1973.
The Regulatory Guide currently allows 2% or 3% of critical damping for piping systems and 7% for reinforced concrete structures compared to 0.5% and 5% of critical damping which were used for piping systems and reinforced concrete structures, respectively, in the original analysis. The greater damping values reduce the structural response compared to the damping values used in original PG&C N
analysis.
!!awever, in many other areas also the reanalysis is being performed using current practices, most of which are more severe dian those used in the original analysis.
In recent discussions, consultants to the ACRS have raised a nu;nber of questions and co:rcaents about whether the damping values in the Regulatory Guide are adequately justified by experimental data, at least for the site conditions in this case.
FGE and the FK staff are currently considering the consultants' coaments and questions and will respond to them in the near future.
(4) General Comment Because of conserva: isc.s in the design methods, materials properties and structural response comoutations used in the
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, design of. nuclear power plants, a plant designed for a given ground motion has a considerable margin of safety to withstand greater ground motions. Based on observations, laboratory tests, and field exp3rience properly designed structures and equipment can be expected to survive earthquake motions that are considerably greater than the values for which they are designed.
III.6 00EsrIou y
Has the Conraission staff ordered any actual testing of the ability of plant components to withstand seiartic stress? If so, please explain which components.have received tests and describe the tests?
RESPONSE
.p Safety related electrical and mechanical equipment is required to be gtmlified to provide assuranc= that it will be able to perform its safety functions before, during and after an earthquake. This can be-done by testing, analysis, or a combination of testing and analysis.
(1) Testing In qualifying Diablo Canyon equipment for the original design basis earthquake, PZE employed testing for most of the safety related electrical, instrumentation and control equipment. This includes
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primarily such items:as ihstruments, logic. and control deirices, batteries and associated equipment,. instrument power supplies, electrical switchgcar and valve actuators. The diesel engines that.
drive the emergency generators were also tested.
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. 'Ihe equipment that was tested consisted mainly of items that, by their nature, were not well suited for qualification by analysis.
The tests consisted of shaking the equipment at a level greater than was calculated at-the equipment's location for a design basis earthquake and monitoring the equipment's performance during and after the shaking. A typical sample of the egai;r.ent involved was tested. The methods and criteria used for conducting the tests are described further in IEEE Standard 344-1971 (Enclosure 16).
For the diesel engine, instead of shaking, a prototype engine was mounted on a barge that was subjected to an explosive shock. The nhWO explosive shock was of shorter duration and had a higher frequency centent then the calculated earthquake cotions, but was far more severe in terms of acceleratica and provided an a.iple test for a massive, very rigid iten such as the diesel engine.
(2) Analysis or Combination of-Testina and Analyis The remainder of the eauipment has been qualified either by analysis or by a combination of testing and analysis. Tnis includes electric motors, the emergency gen?rators that are driven by the diesel engines, pumps and valves.
It also includes passive elements such as walls,, floors, piping, pipe supports 'and panels that contain the instruments and logic devices mentioned above.
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. Some items are too large for any shake table available in the United States.
In these cases the main body of the component is qualified by analysis. Auxiliary items that are mounted on the main body, which are typically more sensitive to seismic motions, are often tested individually.
Some limited generic tests have been performed on reactor coolant system components that are too large for full shaking.
A low level of shaking was applied to gather information about natural frequencies, mode shapes and damping, which are important factors in the seismic analysis of a reactor coolant system. Such tests are described in a Westinghouse Topical Report UCAP-7920, September 1972 (Enclosure 17). Tnese tests were performed on
~ the Indian Point No. 2 nuclear power plant which, like the Diablo Canyon units, is a typical Westinghouse 4-loop plant. Therefore the results are aoplicable to the Diablo Canyon units.
(3)
Future Plans When the reanalysis for the new seismic design basis is performed, the new calculated shaking levels will be compared to the original qualification levels. Where indicated by this comparison, requalification will be performed and/or modifications will be made in the supports and restraints for the equipment involved.
The tIRC staff will require that, where regualification of equip-ment is needed, it be performed in accordance with the newer 4
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e e IEEE Standard 344-1975 (Enclosure 18), with the additional requirements as described in Regulatory Guide 1.100, March 1976, (Cnclosure 19).. In addition, as part of the forthcoming staff -
audit of PG&E seismic analysis and testing, the staff will review all tests to ensure that they adequately characterize the nature and strength of the seismic motions predicted at the mounting location for the particular pieces of equipment involved.
III.7 00ESTIOLi lias the Commission staff undertaken or does it plan to undertake probabilistic epicenter analysis of earthquake epicenter locations along the !!csgri Pault? Will the results of such an analysis influence the Commission's licensing decision?
RESPMSE (1) Safe Shutdmin-Carthouake With respect to large magnitude earthquakes corresponding to the design basis carthquake being used for Diablo Canyon,
~ the staff has not undertaken a probabilistic. analysis but may do so.
For a given site, the safe shutdown earthquake is based on an evaluation of the site's maximum earthquake potential. Norst i
i case assumptions rather than probabilities are used to determine this eart6 quake. The safety related portions of s plant are
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designed to withstand it. The staff has not in the past used probability studies to determine the Safe Shutdown Earthquake or to license plants designed for lesser values.
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. Some members of the ACRS have suggested a probability analysis.
One of the ACRS consultants has recently completed a probability analysis and PG&C is currently performing one.
The staff is considering whether to undertake a probability study or, alternately, to develop conclusions about probability based on a revieu of others' work.
If the staff were to do this,.
the extent to which the results would influence the staff's recom-nendation would depend largely upon how definitive the results were believed to be and on what other information may be available.
Further discussion of the staff's views on how a probability study might be employed is provided in a recent letter to the California Energy Comnission (Cnclosure 20).
Several other bodies, independent of the staff, are involved in the Comnission's decision making process. The staff's conclusions will,be reviewed by the ACRS. Then the Atomic Safety and Licensing Board will consider the matter and render an initial decision. The decision would be subject to review by an Appeal Board and/or the Comnissioners. It is.not known what the attitude of these bodies towards a probability study
.might be.
Ilowever, it seems reasonaole that their judgement would be based on the same factors, ie., the definitiveness of the probability study and 61e availability of other information.
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.. (2) Operating-Basis Earthquake The ' operating Basis Earthquake is a different matter. This earthquake is one that could reasonably be expected to affect the site during the operating life of-the plant. The staff would consider a probability approach in establishing the level of the Operating Basis Earthquake instead of using the normal procedures as described in Appendix A to 10 CFR Part 100. 7he staff.has accepted probability studies for this purpose in a few applications in the past.
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.N NRC SECf.ET ARI AT oace TO: O commissioner O cen. counse XD Exec. DirlOper.
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Subiect-DLant Xd Prepare reply for signature of:
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