ML20209D022
| ML20209D022 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 06/20/1984 |
| From: | Ebersole J Advisory Committee on Reactor Safeguards |
| To: | Palladino N NRC |
| Shared Package | |
| ML20209D027 | List: |
| References | |
| FOIA-86-197 NUDOCS 8406260657 | |
| Download: ML20209D022 (3) | |
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[o, UNITED STATES l',ryj NUCLEAR REGULATORY COMMISSION r
e ADVISORY COMMITTEE ON REACTOR SAFEGUARDS
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June 20, 1984 Honorable Nunzio J. Palladino Chairman U. S. Nuclear Regulatory Commission Washington, D. C.
20555
Dear Dr. Palladino:
SUBJECT:
ACRS REPORT ON DIABLO CANYON NUCLEAR POWER PLANT During its 290th meeting, June 14-16, 1984, the Advisory Committee on Reactor Safeguards reviewed the technical issues described in your letter dated April 13,1984 A Subcommittee meeting was held in Los Angeles, California on May 24,1984 to consider these issues.
During its review, the Comittee had the benefit of discussions with representatives of the Pacific Gas and Electric Company (PG&E ),
the U.S.
Geological Survey (USGS), and the NRC Staff. The Committee also had the benefit of discussions with members of the public, Dr. James K. C rouch, the Comittee's own consultants, and of the documents referenced.
In your April 13 letter you asked that the Comittee review: (a) a license condition that would require PG&E to perform a seismic study to reevaluate the Diablo Canyon design basis; (b) the appropriateness of PG&E taking the lead in the performance of the seismic study; and (c) a recent technical paper by J. Crouch, S. Bachman, and J. Shay, and testimony given before the Comission on that paper.
The license condition referred to in item (a) has been discussed in the Comission Memorandum and Order CLI 84-5 of April 13, 1984 The NRC Staff has developed a proposal as to how this license condition should be imple-mented and has documented its proposal in a letter from R. Jackson to G. Knighton, dated May 7,1984 This proposal requires that PG&E submit a program plan and schedule for implementation by January 30, 1985, and that the program be completed and a final report submitted to the NRC by July 1, 1988.
In our discussions with PG&E representatives, they stated that they are in general agreement with the NRC Staf f proposal of May 7,1984 and will submit a program plan by January 30, 1985 We believe that the elements outlined in the NRC Staf f's proposal will provide a suitable basis for the seismic re-evaluation.
We believe also that the NRC Staff's proposal is responsive to the July 14, 1978 ACRS letter in which the ACRS suggested "that the seismic design of Diablo Canyon be reevaluated in about ten years taking into account applicable new information."
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Honorable Nunzio J. Palladino June 20, 1984 The NRC Staff has proposed to undertake an independent evaluation in parallel with the PG8E ef forts.
In this program, technical assistance work and limited independent analysis would be utilized as needed for the NRC Staff's review of the PG&E work.
The main elements of the NRC Staff's plan for its activities are outlined in its May 7,1984 letter.
We believe that it is appropriate for PG8E to take the lead in the seismic reevaluation and that the NRC Staf f's independent evaluation can provide adequate review of the PG8E work.
We recommend that the NRC effort include a significant support role for the USGS in this regard.
We note that the seismic reevaluation includes the performance of a PRA.
We believe that useful insights from the PRA would best be gained by PG8E if their personnel have an active role in this work.
We, with tt ri assistance of our geological and seismological consultants, have reviewed the contents and implications of the paper by J. Crouch, S.
Bachman, and J.
Shay, entitled, " Post-Miocene Compressional Tectonics Along the Central California Margin."
We have also reviewed the testimony on this paper given before the Commission on March 26-27, 1984 We do not believe that the findings in this paper indicate the need for any immediate revision of the seismic design basis for Diablo Canyon.
It is to be expected that new geological and seismic information will continue to be developed in the future here as well as elsewhere.
In addition, there will be improved understanding in the seismic response and capability of nuclear power plants.
A systematic framework for evaluating this information would be useful. The proposed seismic reevaluation plan should provide such a basis in part.
We request that we be given the opportunity to review and comment on the PG&E program plan and schedule.
We request also that the NRC Staff meet with us as appropriate to discuss their evaluation of the PG&E work.
We recommend consideration of our consultants' advice concerning the proposed seismic reevaluation, including:
Analyses should include inelastic response of the plant structures under strong earthquake ground motion.
Near field strong ground motion above a thrust f ault, including the possibility of a strong velocity pulse, should be considered.
All components of near field strong ground motion should be included in the analysis simultaneously.
Torsional and rocking input ground motion should not be ignored.
Three-dimensional soil structure interaction should be employed to provide estimates of structural response.
i Honorable Nunzio J. Palladino June 20, 1984 Advantage should be taken of existing proprietary seismic profile and well data.
A critical review and evaluation should be made of the regional tectonic structure as well as the onshore and near offshore faults at the site in light of the new evidence that they may connect with an underlying thrust fault.
Based on the infonnation developed in these meetings and considering the above comments, we find no reason to alter the conclusions stated in the Committee's report dated July 14, 1978 regarding operation of this nuclear pl ant.
Sincerely,
/% $. hL,dC Jesse C. Ebersole Chai rman Attachments:
ACRS Consultants' Reports (Ref. 7)
References:
1.
Letter from S. Mendes, Stanley H. Mendes, Inc., to R. Savio, Advisory Committee on Reactor Safeguards,
Subject:
Diablo Canyon Nuclear Power Plant, dated June 4,1984 2.
Letter from Alberta Rich, to R. Savio, Advisory Committee on Reactor Safeguards,
Subject:
Seismic Hearings in Los Angeles on May 24, 1984, dated June 1, 1984 3.
Technical Paper entitled, " Post-Miocene Compressional Tectonics Along the Central California Margin," by James K. Crouch, Steven B. Bachman, and John T. Shay, Nekton, Inc.
4 Transcript of Diablo Canyon Commission Meetings on March 26, 1984 (pp.103-135) and March 27, 1984 (pp. 138-165) 5.
Letter from R. Jackson, Division of Engineering, NRC, to G. Knighton, Division of Engineering, NRC,
Subject:
Status of Draft Elements for the Diablo Canyon License Condition, dated May 7,1984 6.
Letter from R. Jackson, Division of Engineering, NRC, to J. Knight, Division of Engineering, NRC,
Subject:
Preliminary Summary and Evaluation of Article Containing New Infonnation or Interpretations of Faults in the Near Of fshore of Central Coastal California (includ-ing the Hosgri Fault Near Diablo Canyon), dated May 21, 1984 7.
Mvisory Committee on Reactor Safeguards Consultants' reports from B. Page, dated May 29, 1984; G. Thompson, dated May 30,1984; J. Max-well, dated June 16, 1984; E. Luco, dated June 11, 1984; and M. Trifunac, dated June 14, 1984 regarding Diablo Canyon Nuclear Power Plant
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STANFORD UNIVERSITY STANFORD, CALIFORNIA 9005
>EPARTMENT OF GEOLOGY
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Dear Dave and Dick:
The following remarks pertain to the findings of Dr. James Crouch et al., as presented at the meeting held in Los Angeles on May 24, 1984 Main conclusions:
1, I think the staff's draft elements for the Diablo Canyon License Condition are very good indeed. They appear to provide logical procedures for dealing with the seismotectonic problems that are now arising and those that may arise in the future. There will surely be a nearly continuous inflow of data.2, At the present moment, the latest findings (published by Crouch et al.)
rega-ding the Hosgri and other offshore faults do not necessarily increase the maximum ground motion that right be experienced by the Diablo Canyon plant, and do not necessarily increase the frequency of strong earthquakes, As mere information is acquired, the implications could be either more faverable or less favorable to the perceived safety of the plant.
Further ce==ents:
If the offshore Hosgri fault dips landward beneath the Diablo Canyon plant, the vertical distance from the rite to the fault could be either greater.or less than the horizontal distance from the plant to the surface trace of the fault, depending on the curvature of the fault profile, which has not been established.
In any case, it is highly ur_iikely that a strong earthquake would be generated at a depth less than E-10 km, as a certain amo.uf. of confining pressure is required. If the Hosgri f ault were to pass under the plant at a vertical distance of 3 km, say, it would be totally un-ealistic to postulate a strong earthquake stec=ing frcm the fault directly beneath the plant.
The moderate to inconspicuous disturbance of the uppermost strata near the Hosgri fault, as seen in Dr. Crouch's reflection profiles, would argue for very infrequent (or very small) slip-events if the Hosgri fat't is largely a thrust fault. However, we cust not be too optimistic, as we nill do not know for sure what the size and recurrence interval are for slip-events on the fault.
A downward-flattening, thrw4-Hkw etnfi ration would make it highly i4 yv t
' l ur.likely that the Hosgri fault has accrued 80-150 km of strike-slip. The fault would be characterized by predominant thrust-or oblique-slip, and the vibratory motion r.ight differ somewhat from that which has been envisioned for the Diablo Canyon site. Whether the SSE and the ground motion would be more severe or less severe remains to be seen. It may turn o.rt that, if all other factors were equal, an SSE from a thrust fault would be more severe than an SSE from a strike-slip fault. However, if the Hosgri f ault is really a thrust fault, the "ner" Hosgri may be sho-ter than the "old" Hosgri fault. It may not be a part of the San Gregorio zone, after all.
It may not have a history of large slip-events. So, the various factors, when co=bined, may give a result co=patible with the earlier postulations.
Sincerely, kh1.P 3enja=in M. Page Ccpies sent to er.ch addressee.
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C. Siess and D. Okrent, ACRS Subcommittees on Diablo Canyon and Extreme External Phenomena From: George A. Thompson, ACRS consultant Subj ect : May 24 meeting in los Angeles and my evaluation of the new techni, cal data on the Hosgri fault Two important new sets of data bear on the ' tectonic setting of the Diablo plant :
(1) high resolution seismic reflection sections which show east-dipping thrusts along the Hosgri trend (Crouch et al,1984) and (2) earthquake f ocal mechanisms that show thrusting at the latitude of the plant, right-oblique thrusting near San Simeon, and right-lateral slip north of San Simeon (J. Eaton, USGS, manuscript, as quoted at the meeting but not yet available).
I had the privilege of inspecting several of Crouch's seismic sections (as opposed to the line dracings in his published paper), and I believe that his interpretation of thrusts in the Hosgri f ault zone is substantially correct.
In'the light of the new evidence we now need a reexamination of the regional tectonic movements and we need a reassessment of details near the plant. My preliminary analysis is as'follows:
(1)
North of the Monterey Bay evidence is stron; for more than 100 km of horizontal displacanent west of the San Andreas fault.
The paper by Clark et al,1984, in the same volu=e with the Crouch et al paper, develops the evidence f rom Pt. Reyes to Monterey.
I think this zone of displacement might extend southward west of the Santa Maria basin instead of connecting with the Bosgri f ault.
The-Hosgri zone always looked too segment'ed to be a major strike-slip f ault, and that interpretation was accepted as a worst case.
(2)
The M 7.3, 1927 lompoc earthquake was debated at length in earlier reviews, and I concluded (partly on evidence of sea-bottom ef f set in reflection records) that it was most likely associated with the Transverse Range structures and not with the Hosgri f ault.
Because the earthquake data are old and not totally convincing, it was possible to assume that the lompoc earthquake occurred on the Hosgri f ault -- again a worst-case assumption.- both points (1) and (2) add a measure of re. assurance for Diablo Canyon.
I recor: mend (1) a critical review and evaluation of the regional tectonic questions such as those noted in the preceding paragraph, (2) ind epend ent examination of the relevant seismic reflection records, (3) review and reconsideration of all onshore and near-off shore f aults in light of the new evidence that they may connect with an underlying thrust f ault (at what depth?)
i (I consider this to be potentially the binest problem.), (4) analyze the
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I am not sufficiently
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. C. Siess cnd D. Okrent May 30, 1984 ACRS SubecmmittOO expert to make any independent prediction of the outcome of an engineering restudy recommended in point (4).
To put some perspective on the new developments at Diablo Canyon, I agree with Ja'mes Devine of the U.S. Geological Survey who was quoted by the It's NRC staff as regarding the new information to be "not startling".
reassuring that the Hosgri does not appear to be a major strike-slip f alt.
We have always known that there were reverse f aults and therefore a component of compression perpendicular to the San Andreas fault in the region. We also know that regionally the maximum principal stress in California is oriented north-south to slightly clockwise of that direction, and this explains the dominant movements such as the San Andreas. Preliminary staff '
estimates of the design consequences of the new findings suggest that the changes will not be drastic.
I tend to agree in the sense that most of the geologic f actors will likely make hazard estimates smaller, but the geometry of the underlying thrust fault still needs to be evaluated in detail.
- And, as stated before, I am not prepared to make any estimate regarding the engineering ealculations.
In su= ary, my inf or=ation so f ar as it goes, indicates that Diablo Canyon could be s af ely allowed to operate while review and re-study is continu ed.
In forming this opinion, however, I must rely heavily on preliminary statements of the NRC staf f and U.S. Geological Survey consultants.
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/953 6/16/84 SEISMICITY RELATED TO THE HOSGRI FAULT ZONE By John C. Maxwell High quality reflection seismic surveys covering the Hosgri Fault zone southwest of the Diablo Canyon Nuclear Plant site clearly show a dominant pattern of easterly dipping thrust faults which are steep near the surface and flatten with depth (Crouch, Bachman and Shay,1984).
There is no evidence in this data for a through going major strike slip fault such as that postulated in arranging the SSE for the plant.
Small, subsidiary vertical faults locally displace the ocean bottom sediments demonstrating recent faulting.
Some amount of strike slip motion may be involved in this part of the fault zone, but it has not been large enough to generate a through going master fault.
Evidence for strike slip faulting on the Hosgri zone is indirect, depending mainly on an assumed connection to the San Simeon - Point Sur San Gregoria fault zones to the north.
Seismic studies of earthquakes along this trend (Eaton, $1984) shew right lateral horizontal slip on vertical northwesterly trending planes within the Point Sur-San Simeon trends, with obligue faulting near San Simeon, while to the south near Point Sal and Santa maria, deformation along the Hosgri and parallel trends occurred by southwesterly. directed overthrust faults.
Eaton's observations support the interpretation of their seismic data by Crouch, et al.
Questions ven that faulting offshore from the Diablo Canyon plant is dominantly thrusting rather than strike-slip displacement:
(1) What magnitude of earthquakes might be generated here?
(2) What faults, if any, continue beneath the plant site? Do the faults die out within a sub-horizontal sedimentary section (possibly somewhat broken at depth), or do they cut into basement rocks?
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2-(3) What is the nature of the basement beneath the plant site.?
Are Basement rocks rigid (Salinian crystaline rocks), broken (Fransician melange) or layered (Great Valley or Coastal Facies Francisian)?
(4)
Is there evidence indicating upthrusting of basement rocks beneath the plant site?
Opinion The SSE of 7.5 was based on the presumed presence of a major strike slip along the Hosgri zone.
It does not seem likely that a fault of this magnitude would result from the thrust faults and folds mapped seismically by Crouch, et al.
The question of possible basement involvement in the thrusting is crucial. A magnitude 6.4 (San Fernado,1971) to 7.3 (Lompoc 1927 (7)).
may be anticipated if rigid basement is involved.
Only smaller earthquakes would be anticipated if faults are confined to overlying sediments and do not displace rigid basement rocks.
Faults near the plant site have been detennined to be not capable.
Therefore, no active segment of an underlying thrust fault appears to be present beneath or adjacent to the plant site. An SSE of mag 7.5 does indeed seein to be adequately conservative.
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Dr. R. Savio Senior Staff Engineer Advisory Committee on Reactor Safeguards U.S. Nuclear Regulatory Commission Washington D.C. 20555
Dear Dick:
Since I will not be able to attend the June 14 meeting in Wa shington D.C.,
I am sending a f ew comments in connection with the matters discussed at the Los Angeles meeting of May 24, 1984.
With respect to the seismic revalidation study proposed as license condition I have the following comments:
a)
To increase the credibility of such a study I believe that it would be necessary that the data to be considered, the methods of analysis and the various modelling assumptions be established by consensus by a group specialists representing PG &
E, NRC staff and ACRS.
The calculations would then be performed by PG & E or its consultants.
b)
As I suggested at the May 24, 1984 subcommittee meeting in Los Angeles I believe that analysis of the accelerograms obtained within and in the vicinity of the Diablo Canyon Plant should be part of the proposed study.
These records contain valuable information as to the effects of soil-structure interac-
- tion, foundation embedment and spatial variation of ground motion.
The records can also be used to validate low amplitude structural models and analysis techniques.
c)
The proposed study should include analysis of the inela'stic response of the Diablo Canyon plant structures under strong earthquake ground motion.
With respects to the implications of the paper by Crouch, Bachman e-shay I have the following comments:
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(a)
Recent theoretical studies (e.g. Anderson and Luco, B.S.S. A., 73, 4 5-5 7, 1983) suggest that the motion on the upper block on a thrust fault configuration can be higher than that for a vertical strike-slip fault for the same slip on the fault.
The correlations developed by Campbell (1983) also show higher peak accelerations for thrust faults for the same magnitude and distance.
The differences between strike-slip and thrust faults apparent in the correlations are probably influenced by the San Fernando 1971 thrust earthquake.
A recent April 1984, M = 6.2 strike-slip earthquake in the vicinity of San Jose produced a record on the fault with a peak acceleration of 1.3g.
The records obtained in this earthquake will probably increase the estimates of peak acceleration for strike-slip earthquakes and will reduce the differences between strike-slip and thrust events.
(b)
The possibility that the distance from the site to the Hosgri fault may by as short as 2.5 km raises some concern in my mind.
Records at short distances to f aults (less than 5 km) reveal a strong velocity pulse (peak velocities excess of 100 cm/sec) of considerable duration.
This type of pulse can be damaging to structures stressed into the inelastic range.
Sincerely yours, l
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6 7- /75h June 14, 1984 Sunnary of Connents by M. D. Trifunac Made During the June 14, 1984 ACRS Meeting Washington, D.C on Reevaluation of Diablo Canyon Seismic Design At present an effort is being considered to reevaluate the seismic design criteria for the Diablo Canyon nuclear power site in California.
It has been proposed to complete this reevaluation by 1988 and to incorporate into enalyses all current geological and seismological information.
Since the ultimate objective of this effort is to formulate and implement specific engineering design and analysis to verify the adequacy of safety related structures and components, may I suggest that the following be considered during the course of this work.
1.
Modern and advanced methods should be employed throughout the reevaluation with proper consideration of their uncertainties which cannot be resolved at present.
For example, the following would be emphasized in the analysis:
a.
Near field strong ground motion above a thrusting fault should be considered.
b.
All components of near field strong ground motion should be
'ncluded in the analysis simultaneously.
Torsional and i
rocking input ground motion should not be ignored.
Three-dimensional soil structure interaction should be
'femployedtoprovideestimatesofstructuralresponse.
pDamping in structures should be allowed to increase with response amplitude but should not be set to a high constant 0
value throughout the entire response.
"Effect" reduction of
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spectural amplitudes should be excluded from any stage in the analysis.
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M. D. Trifunac Coments d.
Non-linear structural response to simultaneous base excitations with 6 degrees of freedom for input strong ground motion should be considered.
Methods and knowledge are available to carry out such analyses, but it is essential to balance all procedures into the overall package properly emphasizing all relevant steps.
For example, the fault geometry, magnitude or rate of slip on Hosgri fault, as uncertain as those may be, may not be the principal contributors to the ultimate uncertainty of the engineering estimates of structural response.
2.
Ari independent group of experts could be retained to carry out or to direct the work on the key elements of the reevaluation task.
This might help the NRC Staff by contributing through outside independent expertise to their ongoing reevaluation program. This would also also be very advantageous to the ongoing PG&E effort is
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that it would help them to promote, support and benefit from more agressive and modern engineering analyses, beyond the " routine" current interpretations of the design criteria.
3.
Unless some qualitative " jump" can be incorporated into the proposed reevaluation of the seismic design procedures and criteria for the Diablo Canyon site in California, it seems to me that we might experience a " repetition" of the difficulties exemplified there during the past 10 years.
4.
An experimental verification program would be very helpful for reducing a number of uncertainties in the analysis and response characterization.
The program would include:
(1) the analysis of the strong motion data recorded in and near the structures at the Diablo Canyon site, and (2) low amplitude vibration tests of selected structures to verify the analytical calculations.
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