ML20212M302
| ML20212M302 | |
| Person / Time | |
|---|---|
| Site: | 05000000, Diablo Canyon |
| Issue date: | 01/30/1975 |
| From: | Harold Denton Office of Nuclear Reactor Regulation |
| To: | Deyoung R Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20150F500 | List:
|
| References | |
| FOIA-86-391 NUDOCS 8608250434 | |
| Download: ML20212M302 (15) | |
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i JAN 3 01975
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l R. C. DeYoung, Assistant Director j
for Light Water Reactors, Group 1, RL SUPPLEMENT TO SAFETY EVALUATION REPORT FOP, GEOLOGY, SEISMOLOGY AND FOUNDATION ENGINEERING PLANT NAME: Diablo Canyon i
LICENSING STAGE: OL DOCKET NUMBER: 50-275/323 RESPONSIBLE BRANCH: LWR l-3 REQUESTED COMPLETION DATE: NA APPLICANTS RESPONSE DATE NECESSARY FOR NEXT ACTION PLANNED ON PROJECT: NA DESCRIPTION OF RESPONSE: NA REVIEW STATUS: Supplement I to SER Complete Enclosed is a supplement to the Diablo Canyon Safety Evaluation Report prepared by W. Gamanf11 R. McMullen, R. Hofmann, J. Stopp and L. Heller for your use. The changes were necessitated by our further review of the offshore geology and seismology.
DISTRIBUTION:
%W by TR: DOCKET FILE M Moe TR:SAB Harold R. Denton, Assistant Director TR*RDG g
for Site Safaty Division of Technical Review Office of Nuclear Reactor Regulation l
Enclosure:
j As stated l
cc w/o encl:
A. Giambusso l
W. Mcdonald J. Panzarella cc w/ encl S. Kanauer R. McMullen F. Schroeder R. Hofmann SS Branch Chiefs J. Stepp A. Kenneke L. Heller hWf O. Parr T. Hirons f,
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2.5 Geology and Seismology This geology and seismology evaluation reflects our review of investigations conducted since 1969. These investigations are des-cribed in the Final Safety Analysis Report (FSAR) for the Diablo Canyon Nuclear Plant site and in a report by Wagner (1974).
The geology and seismology of the Diablo Canyon site was reviewed by the AEC staff and its geological and seismological advisors, the U. S.
Geological Survey (USGS) and the U. S. Coast and Geodetic Survey, during the construction permit review.
The findings of that review were published on November 18, 1969, I
as part of the SER for Unit 2.
With respect to sefsmic design input, the SER concluded:
E (1) "There are no identifiable major faults or other geologic structures in the area that could be expected to localize seismicity in the immediate vicinity of the site. The nearest seismically active major fault is the Nacimiento fault, a northwest-trending fault zone that approaches to within about 18-20 miles of the nice to the northeast," and (2) ".... the Coast and Geodetic Survey agrees with the applicant's statement of 0.20s at the site and on rock for the predicted maximum ground accelerations of the design earthquake and twice that value, 0.40g on the rock for the safe shut-down conditions."
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2.5.1 Geology Since publication of the 1969 SER, studies of the geologic structure offshore of the site have been reported (Hoskins and Griffiths, 1971; Wagner, 1974). These studies revealed significant geologic structure offshore of the.Diablo Canyon site. To determine the detE11ed structural relationships in the immediate offshore region, the applicant cendant. extensive high' resolution geophysical investigations along that reach of the structure. Profiles obtained by the applicant were made available to the USGS and those obtained early in the investigation were included in the independent interpretation of the offshore structure by Wagner (1974).
The applicant's interpretation, together with a summary of the results presented by Hoskins and Griffiths (1971) and Wagner (1974), are included in the FSAR for the Diablo Canyon site.
l The Hoskins and Griffiths (1971) paper gives the results of an interpretation of extensive deep penetration seismic reflection surveys a'
along the California Coast. The surveys revealed a structural basin
. -g offshore of the southern Coast Ranges which they called the Santa l
Maria basin.
It is described as being a shallow, synclinorium about 140 miles long and 25 to 30 miles wide. Structural grain within the basin trends northwest parallel to the trend of the basin. Major faults bound the basin on both.the east and west. The eastern border fault as identified by Hoskins and Griffiths passes within about 5 miles of the Diablo Canyon site.
It is about 90 miles in total length.
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2 - 10 Wagner (1974) utilized deep penetration seismic reflection methods and high resolution seismic -acoustic surveys. The configuration of the sea floor was obtained using precision bathymetic data and, locally, by side-scan sonar. These provided a considerable refine-ment of the structure along the eastern boundary of the Santa Maria basin in the region between Cape San Martin and Point Sal. The basin is indicated to have formed in Middle to Post-Miocene (26 m.y.) time.
It'contains from 2,000 to 5,000 ft of Miocene sediments unconformably overlain by up to 3,500 ft of Pliocene (7 m.y.) section. An erosion surface is indicated to have formed on these Tertiary beds during Pleistocene time. Post-Wisconsinan sediments, deposited during the past 20,000 years, overlie much of the Tertiary erosion surface.
Wagner (1974) concurs with the interpretation of Hoskins and
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Griffiths (1971) that a major fault zone forms the eastern boundary of the offshore Santa Maria basin. He calls it the Hosgri fault.
In structural detail the Hosgri fault is a zone containing from 2 to 5 subparallel splays. These faults locally ' offset Tertiary and Pre-Tertiary rocks with apparent vertical offsets ranging between 1,500 and 6,000 ft.
The fault is discontinuous and segmented in the late Tertiary and Quaternary section. The applicant interprets the East Boundary Zone (the Hosgri fault zone of Wagner, 1974) as'being the boundary between synclinal downwarping of the offshore Santa Maria basin and regional uplift of the southern Coast Ranges. The style of faulting in the zone is extensional as shown by its locali-zation along the flank of a regional upwarp and by its pattern of e
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basin down-normal faults and crested f aults along the flank of local structural highs at Point San Luis and Point Piedras Blancas. - Reverce drag downfolding is also shown in the strata adjacent to the normal faults, and is likewise characteristic of extensional deformation.
Normal faults with east-facing scarps have also been identif1ed and are interpreted as being antithetic faults of the overall extensional system. The applicant states that due to the lack of evidence for compressional deformation in the Pliocene and Pleistocene and the presence of the positive evidence for extensional deformation, the
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Santa Maria basin is in a region that has probably been characterized by extensional strain during much of the time since initial deposition n,
in the basin during the Miocene.
While the movement on the fault zone was predominantly vertical during Tertiary, Wagner (1974) cites evidence of lateral (strike-slip)
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movement in the upper section. Earthquake focal mechanisms for this zone determined by the applicant support a strike-slip component of movement. Thus vertical movement on the fault may currently be sub-ordinate to strike-slip.
Evidence of recency of movement on the Hosgri fault zone is found in offsets of the sea floor together with offsets of the Post-Wisconsinan sediments. Wagner (1974) found these offsets on three of his profile crossings of the zone. On other high resolution seismic profiles, offsets of the base of the Post-Wisconsinan sediments are observed but with no offset of the sea floor. Still other profiles show no offset of the Post-Wisconsinan sediments. This pattern of offset is 6
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lan217 suppet ted by the applicant's investigations.
We, thereforc, conclude that the Hosgri fault zone must be considered capable within the meaning of 10 CFR Part 100 Appendix A, Section III (1).
The applicant places the east boundary of the Santa Maria basin in his seismic potential category of Level III which is defined as
" Potential for earthquakes resulting chiefly from movement at depth with no surface faulting, but at least with some possibility of sur-face faulting of as much as a few miles strike length and a few feet of slip." Although current movement on the Hosgri fault zone appears to be limited to local fault segments, we assume for the purpose of establishing the safe shutdown earthquake (SSE), that the fault is continuous, 90 miles long, capable, and located 3-1/2 miles west of the site at its closest approach.
In its geological input to the Safety Evaluation Report, dated M
28 January,1975 (Appendix D of this report), the USGS concluded that the East Boundary (EBZ) zone and the Santa Lucia Bank zone "should be considered inextricably involved with the strike-slip fault mechanics of plate boundary motions that are currently concentrated along the San Andreas fault." The USGS further concluded that earthquakes along the EBZ should not be expec.ted to be as large as those expected q
along the San Andreas, but that based on the limited information on the Santa Lucia Bank fault, "the occurrence of an earthquake as large
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as events characteristic of subparallel strike slip faults, which bound basins, such as the Santa Maria...." could not be precluded.
In the Seismology section of that report the USGS concluded that i
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"with the limit cf the present information as to the interpretation of the relationship of the East Boundary fault to the Santa Lucia Bank fault, an earthquake similar to the November 4,1927, event but occurring along the East Boundary Zone or the Santa Lucia Esak fault zone represents the maximum earthquake that is likely to occur near to the s'ite."
These conclusions consider the structural properties and extent of the Santa Lucia Bank fault to be the same as those of the Hosgri fault zone and, further, that the Santa Lucia Bank fault was the source of the November 4,1927, earthquake. We are pursuing a comparative evaluation of these two tectonic zones and will report the results in a further supplement.
2.5.2 Vibratory Ground Motion Our SER (1969) for the Diablo Canyon Unit 2 concluded that one of the following four possible earthquakes would result in maximum accelerations at the site:
g Earthquake A: Magnitude 8-1/2 along the San Andreas fault 48 miles from the site, resulting in a ground acceleration of 0.10g at the site.
Earthquake B: Magnitude 7-1/4 along the Nacimiento fault 20 miles from the site, resulting in a ground acceleration of 0.12g at the site.
Earthquake C: Magnitude 7-1/2 along the off-shore extension of the Santa Ynez fault 50 miles from the site, resulting in a ground acceleration of 0 05g at the site.
Earthquake D: Magnitude 6-3/4 af tershock near the site associated with Earthquake A which results in a ground acceleration of 0.20g at the site.
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For design purposes, an envra.cpe of the B and D response spectra was used.
The operating basis earthquake (OBE) encompassed Earthquake B with a horizontal acceleration of 0.15g and Earthquake D with a horizontal acceleration of 0.20g.
The use of two earthquake response spectra for the OBE was selected because the frequencies of ground motion for the two earthquakes would be different in consequence of unequal attenuation due to carthquake location, i.e., earthquake D would have relatively higher accelerations in the high frequency part of its spectrum. The same spectra and 0.40g were used for the SSE.
The earlier conclusions regarding the geologic structure of the region and its relationship to earthquake occurrence have been altered by the subsequent detailed offshore investigations discussed al' re.
We have made a specific evaluation of the potentia} of the Hosgri fault zone as an earthquake generator, using appropriate regional relationships between earthquake size and fault dimensions (Bonilla, 1970) and amodg magnitude, acceleration and epicenter distance (Schnabel and Seed, 1973). We have considered the Hosgri fault zone to have a maximum length of 90 miles as defined by Hoskins and Griffiths (1971), to have the potential for breaking over one half its total length in a single earthquake and to have a mechanism that is inter-mediate between strike-slip and dip-slip.
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Observations have been made o8 che relationship os fault rupture length to magnitude and fault displacement by Bonilla (1970).
Rupture length is seldom fully observed on the surface of the earth.
Often the slip surface on a fault plane is at depth and only a portion of it intersects the surface, or soil cover masks the ends of the rupture zone where displacements are small. Bonilla (1970) recognizes this by drawing a line on his plot of rupture length versus magnitude to include all observations. That line corresponds well with data fron earthquakes which have occurred on the San Andreas fault
( Alge rmissen, 1969). The crust of the earth along the California coast is thin compared to length of the Hosgri fault zone. Thus the shape of the fault slip surface for the Hosgri fault zone would be similar to that for the strike-slip San Andreas and would have similar near field energy distribution characteristics. However, to account gqppgg for a potential dip-slip component on the fault, some additional conservatism in determining the magnitude was considered beyond that indicated by Bonilla (1970).
Bonilla's graph may be used to estimate maximum magnitude nasuming that a fraction of the known total length of a fault may rupture in a single earthquake. Data indicating that no more than 1/2 of the total fault length is ruptured during any single earthquake has been presented by Tocher (1958), Bonilla (1970) and Albee and Smith (1966).
With the above considerations, a magnitude 6.6 carthquake could be derived for the maximum earthquake on the Hosgri fault zone.
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2 - 16 At a distance of 3.5 miles, the Diablo Canyon s1ce lies witnin the near-field of seismic radiation from a potential magnitude 6.6 earthquake on the Hosgri fault zone. A few pulses of high accelerations
- are, therefore, expected at the site in addition to lower accelerations continuing for the expected duration of strong shaking.
Graphs of peak acceleration versus distance and magnitude have been i
developed to account for the high acceleration pulsas recently recorded very close to earthquake epicenters, (Schnabel and Seed,1973). These graphs, considering the mechanism of the Hosgri fault indicate a peak near field acceleration at the site of 0.5g.
Because the expected acceleration would be in the near field, a spectral envelope for checking design was determined by scaling two near field records of earthquakes having magnitudes and at distances that bracket the Diablo Canyon site-source conditions for the Hosgri fault. The HERNEk records were chosen from instruments located on foundation materials as similar as possible to those at the site. These records were scaled to 0.5g maximum acceleration and their response spectra were compared to that used for the SSE seismic design.
Spectra were used from the M-5.6 1966 Parkfield, California earthquake recorded at 3.2 miles from the fault. When scaled to 0.5g this provides a conservative estimate of the high frequency portion of the expected spectra from the Hosgri fault. Spectra recorded at 18 miles from the M-6.5 1971 San Fernando earthquake was also used. At this distance, high frequency spikes are well attenuated. Thus when scaled to 0.5g, this spectrum provides overly. conservative spectral values for intermediate and longer periods, t
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2 - 17 e l Comparison of these spectra and the spectra used by the applicant for design of the Diablo Canyon units shows the design spectra to be exceeded only over limited frequencies. Because of the conservatism of the seismic-response spectra used in the design, a 0.5g SSE (the value for a maximum earthquake on the Hosgri fault determined by the procedure described above) would require only minimal changes to the seismic design. Our evaluation of the maximum earthquake potential of the Hosgri fealt zone must, of course, be considered tentative pending our further evaluation of the structural and seismic properties of the Santa Lucia Bank and Hosgri fault zones.
2.5.3 Slope Stability The stability of the cut slopes adjacent to the plant was evaluated by the staff and its 'dvisor the Corps of Engineers. The a
report of the Corps of Engineers, which is enclosed as Appendix C to NdNONEd this report, stated that the exploration, sampling, and testing was sufficient to define soil properties, the methodology used in the dynamic analysis is consistent w1th the latest state-of-the-art techniques, and the results are conservative. They concluded that "the calculated maximum displacement of 10 inches, resulting from the selected double design earthquake should not causa damage to structures located near the toe of the cut. However, provisions should be made to insure that the condition of the material on the slope is not altered, particularly by saturation due to poor surface drainage."
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2 - 18 We have reviewed the stability of the cut slopes and the provisions for drainage to preclude saturation by groundwater, and have concluded that the slopes will remain stable during the occurrence of the SSE, and that Category I structures will not be damaged.
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REFERENCES Algermissen, S. T., (1969). Studies in Seismicity and. Earthquake Damage Statistics; Three parts, Summary and Recommendations, 23 pages; Appendix A, 142 pages; and Appendix B, 68 pages, Prepared for the Department of Housing and Urban Development, Office of Economic Analysis by the Staff and Consultants of the Department of Commerce, ESSA, Coast and Geodetic Survey.
- Albee, A".
L., and Smith, J.
L.,
(1966). Earthquake Characteristics and Fault Activity in Southern California; Special Publication of The Los Angeles Section of the Association of Engineering Geologists, Arcadia, California, pp. 9-33.
Bonilla, M. G. (1970).
Surface Faulting and Related Effects, in Earthquake Engineering, Robert L. Wiegel, Coord., Ed., Prentic-Hall, Inc., Englewood Cliffs, N. J.
Hoskins, E.
C.,
and Griffiths, J.
R., (1971).
Hydrocarbon Potential of Northern and Central California Offshore;.'American Assoc. Petroleum Geologists, Memoir 15, pp. 212-228.
Schnabel, P.
B., and Seed, H.
B., (1973). Accelerations in Rock for Earthquakes in the Western United States; Bul., Seis. Soc. Am., V.
No. 2, p. 501-516.
e Tocher, D. (1958).
Earthquake Energy and Ground Breakage; Seism.
Soc. Amer. Bull., Vol. 48, p. 147-153.
titullawm Wagner, H.
C., (1974). Marine Geolo Pt. Sal South-Central California Of,h.gy Between Cape San Martin and pore; U. S. Geol. Survey open file report 74-252.
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2 - 18 We have reviewed the stability of the cut slopes and the provisions for drainage to preclude saturation by groundwater, and have concluded that the slopes will remain stable during the occurrence of the SSE, and that Category I structures will not be damaged.
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REFERENCES Algermissen, S. T., (1969). Studies in Seismicity and. Earthquake Damage Statistics; Three parts, Summary and Recommendations, 23 pages; Appendix A, 142 pages; and Appendix B, 68 pages, Prepared for the Department of Housing and Urban Development, Office of Economic Analysis by the Staff and Consultants of the Department of Commerce, ESSA, Coast and Geodetic Survey.
- Albee, A'.
L., and Smith, J.
L., (1966). Earthquake Characteristics and Fault Activity in Southern California; Special Publication of The Los Angeles Section of the Association of Engineering Geologists, Arcadia, California, pp. 9-33.
Bonilla, M. G. (1970).
Surface Faulting and Related Effects, in Earthquake Engineering. Robert L. Wiegel, Coord., Ed., Prentic-Hall, Inc., Englewood Cliffs, N. J.
Hoskins, E.
G.,
and Griffiths, J.
R., (1971).
Hydrocarbon Potential of Northern and Central California Offshore; American Assoc. Petroleum Geologists, Memoir 15, pp. 212-228.
Schnabel, P. B., and Seed, H. B., (1973). Accelerations in Rock for Earthquakes in the Western United States; Bul., Seis. Soc. Am., V.
No. 2, p. 501-516.
4 Tocher, D. (1958).
Earthquake Energy and Ground Breakage; Seism.
Soc. Amer. Bull., Vol. 48, p.147-153.
tmMWm Wagner, H.
C., (1974). Marine Geology Between Cape San Martin and Pt. Sal South-Central California Offshore; U. S. Geol. Survey open file report 74-252.
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