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DCD 016 GSB RDG MEMORANDW! FOR:
L. Reiter R. Rothman R. McMullen D. Gupta H. Polk FROM:
S. Brocoum, Leader Geology Section Geosciences Branch, DE SUBJECi:
STATUS OF DIABLO CANYON LICENSE CONDITION The current schedule for developing the specific elements of the Diablo Canyon License Condition (Attachment 1) is:
May 8, 1984: Meeting with PG&E to discuss the specific elements of the license condition (Attachment 2)
May 24, 1984: Meeting with the ACRS Extreme External Phenomena Subcomittee in Los Angeles to discuss the staff proposal for seismic revalidation (Attachment 3).
June 13, 1984: A second meeting, in Bethesda, with the ACRS Extreme External Phenomena Subcomittee, if necessary.
June 14-16, 1984: ACRS Full Comittee Meeting, as required, on the staff proposal for seismic revalidation.
July 19, 1984 (Tentative): Presentation to the Comission of specific elements for the revalidation program for seismic design bases in accordance with the license condition.
If there are any additional comments on the specific elements of the license condition (Attachment 1), please let me have them by Friday, May 4, so I can update the specific elements for the May 8th meeting.
Please be prepared to make a short presentation to PG&E on Tuesday, May 8th, on the elements, or portions of elements, that you prepared.
We will have a short " pre-meeting" on Monday, May 7 to prepare for Tuesday'smeeting.N 0516co h 84050$
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Diablo Canyon Nuclear Plant License Conditions PG&E shall develop and implement a State-of-the-Art Program to revalidate the seismic design bases used for Diablo Canyon.
P0&E shall' submit for NRC staff review and approval the proposed Program Plan and proposed schedule for implementation by January 30, 1985. The program shall be completed and final report submitted to the NRC by July & w,.
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The program shall consist, at a minimum, of the following proposed conditions:
(1) The applicant shall identify, examine, and evaluate all relevant geologic and seismic data, information, and interpretations that have become available since the 1979 ASLB hearing, including but not limited to the following:
.y (a) data collected as a result of research by government agencies
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and"others, and as a result of extensive oi1 exploration off the coast and onshore in central California since 1978, including seismic reflection data, geological mapping, and exploratory well * ~
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boring logs; (b) reprocessed, pre-1979 seismic reflection data obtained by PG&E during licensing activities, and by the USGS during research activities. These data will be selected in critical areas based on the results of (a), and reprocessed using modern techniques.
The final results of these efforts will be used as input to Condit, ion i
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(2)
PG&E shall reevaluate the magnitude of the safe shutdown earthquake. This element shall include reevaluation of the maximum earthquake for the Hosgri fault and also evaluation of the maximum' earthquake on any other capable fault in the site region which might be considered as controlling for the ground motion. The parameters to be considered in this reevaluation are:
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(a) Fault length to estimate magnitude (b) Rupture length to estimate magnitude (c) Slip rate to estimate magnitude (d) Maximum displacement from a single event to estimate magnitude (e) Historical seismicity (f) Other approaches, such as total area of fault to estimate magnitude.
(3) PG&E shall revalidate the ground motion at the site based on the magnitude of the safe shutdown earthquake. -
(a) Perform regression analysis of spectral values to get estimates of both horizontal and vertical spectra for Diablo Canyon (DCNPP) ~
site specific conditions.
(b) Estimate site specific horizontal and vertical spectra.
(c) Perform earthquake numerical modeling study using the most recent techniques calibrated to a suite of nearfield data.
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DRAFT (d) Consider and evaluate the relevant soil-structure interaction effects such as, but not limited to, embedment and foundation averaging.
Both analytical and empirical techniques may be appropriate.
All of the above will take into account the site speci.fic conditions fa
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valid for DCNPP such as: distance to the fault, focal mechanism, attenuation and site geology.
(4) PG&E shall assess the significance of conclusions drawn from seismic reevaluation and revalidation studies in item 1, 2 and 3 utilizing the following two elements:
(a) PG&E shall perform an up-to-date realistic seismic probabilistic risk assessment (PRA) assuming.the seismic capacity of the plant as it is actually constructed. The PRA shall adequately represent the uncertainty involved and include estimates of core-melt and consequences to the public of different ground motion levels up to and beyond the existing seismic design basis.
(b) If the results or the scope of the PRA indicate the need, PG&E shall also make deterministic estimates of seismic capability of
selected structures, systems or components to better estimate existing seismic margins.
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PG&E shall keep the staff inforned on the progress of the revalidation program by quarterly progress reports and by semi-annual meetings in Bethesda. The applicant will also present annual progress reports.to the ACRS subcomittee on Diablo Canyon.
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EXPLA. NATION OF EACH LICENSE CONDITION FOR DIABLO CANYON LICENSE CONDITION 1: UPDATE AND REPROCESS DATA This condition is necessary:
(a) To reexamine the characteristics at depth (2 to 20 km) of the Hosgri fault zene and other fault zones in the vicinity to determine whether.or not they are vertical faults'as assumed in tite-
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past, or low angle thrust faults.
If the latter is true it is necessary to know the approximate depth the faults may be beneath the site. This information is needed to calculate earthquake ground notions at the site.
(b) To confirm the overall length of the Hosgri zone, and, if possible, the lengths of segments that have ruptured during a single earthquake. This information is needed to determine the maximum earthquake the Hosgri is capable of generating; (c) To detemine the effects of the Hosgri fault zone and other faults in the site area on strata ir the shallow subsurface such as, l
seafloor offset and their relation to folding in the shallow sediments. These data are important in calculating the recurrence intervals of large earthquakes used in seismic risk assessment; l
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(d) To confinn that there are no thrust splays of the Hosgri fault zorte-or other faults nearer to the site that have not been detected.
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LICEtiSE CONDITION 2: REEVALUATIOH OF THE SAFE SHUTDOWN EARTHQUAKE The safe shutdown earthquake for Diablo Canyon is based on the assumption of the occurrence of a magnitude (M ) 7.5 earthquake on the s
Hosgri fault 5 km from the plant. The magnitude of the assumed earthquake was estimated from an interpretation of the tectonics of
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elenent of this estimation wa's the assumption that the 1927 Lompoc earthquake (H 7.3) occurred on the Hosgri. This assumption was made s
because the error bounds of the epicentral location of this earthquake are so large that the Hosgri could not be eliminated as a possible source. Another important assumption in the magnitude astimation for j
the safe shutdown earthquake was that the Hosgri is a continuous system of anastomosing faults stretching from the Transverse Range faults to the San Simeon and San Gregorio faults.
Since the completion of the Hosgri reanalysis and the Diablo Canyon ASLB hearings wore information has become available as'to the geology and tectonics of coastal California. This new data and interpretations may have relevance to the magnitude estimation for the Diablo Canyon safe shutdown earthquake.
In addition, the techniques for estimating the possible magnitude of earthquakes from the geologic record have become better understood and more acceptable. These techniques include the estimation of the maximum earthquake magnitude on a fault from the length of the fault, the length of rupture during a single earthquake, the slip rate of the fault, the maximum displacement from a single earthquake, and the area of the rupture surface during an earthquake.
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i DRAFT LICENSE CONDITION 3: REVALIDIATION OF THE VIBRATORY GROUND MOTION BASED ON THE MAGNITUDE OF THE CONTROLLING EARTHQUAKE At the time of the Hosgri reanalysis for Diablo Canyon there was very little strong ground motion data which had been recorded in the near,
field of large earthquakes. Because of this, the spectrum used by Dr,
- Newmark for estimating the ground motion was based solely on the strong
- ground motion of the 1971 San Fernando Valley earthquake recorded at Pocoima Dam. This record had the highest peak horizontal ground acceleration recorded to that time. Since then there have been a number of near field recordings made from larger earthquakes. This enhanced data base has been used to derive predictive equations for vibratory ground motion as a function of earthquake size, distance from source, and site conditions such as geology, and fault type. This data base has also been used to calibrate theoretical numerical modeling studies as a means of improving their reliability. Using the recent data and newly derived predictive methods more certain estimates of ground motion may
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be made.
In the Hosgri analysis the staff, on the recommendation of Dr. Newmark, allowed for reduction of the ground motion for larger structures based on the " tau effect" (foundation averaging). This has been subject to controversy. The " tau effect" is one of several effects, due to the presence of large embedded structures, that may act to modify the level of earthquake motion actually experienced in nuclear plant structures.
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These effects, their interactions and implications may be estiamted utilizing sophisticated analytical and empirical techniques.
t LICENSE CONDITION 4: ASSESSMENT OF SIGNIFICANCE OF CONCLUSIONS FROM ESTIMATION STUDIES The purpose of this condition is to assess the significance of differences, if any, between the existing seismic design basis and that inferred from the,new information presented in the previous tasks.
Since PRA allows us to associate risk with different levels of ground motion, it can be put into context the impact of changing geological,
. seismological and analytical assumptions.
It also serves as a screening device to identify so-called weak links where focussed attention may bring about significant improvement in calculated risk.
If necessary, limited deterministic analysis may be called upon to better define seismic margins in specific selected areas.
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PARALLEL STAFF EFFORTS WITH REGARD TO THE DIABLO CANYON PLANT LICENSE CONDITION Most of the technical work will be provided by PG&E for staff review.
Technical assistance and limited independent analysis will be utilized as needed for the review.
Examples of staff and staff consultant efforts are listed below:
(1) Review and perform some independent analysis of the evaluation of,.
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. c,.. ;:: : o geologic and seismologic data, information and interpretation provided by the applicant and some data we may acquire independently. The staff will be aided by its advisor, the USGS and its consultant Dr. David B. Slemons. Such new data may include seismic reflection profiles which may be available from the oil industry, new exploratory (for oil and gas) well data,. publications in geology, tectonics, and seismology about the central California Coast.
(2) The staff will make independent assessments of and review the l
.i applicants revalidation of the magnitude of the safe shutdown earthquake. The staff will be assisted by the U.S.G.S. and Dr.
David B. Slemons.
(3) The staff will review with our advisors, the U.S.G.S. and the 1
l National Laboratories, the Applicant's ground motion estimates and ~
soil-structure interaction studies. Utilizing recent USGS and other studies, the staff will make independent estimates in selected areas of groundmotion.
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(4) The staff, with the assistance of the USGS and National Laboratories, will review the PRA.
(5) The staff, through a National Laboratory, will set up a senior advisory review panel to advise the staff on technical issues on the seismic. revalidation, pg
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APR 2 61984 Docket Nos.: 50-275 and 50-323 MEMORANDUM FOR: George W. Knighton, Chief Licensing Branch No. 3 Division of Licensing FR0ft:
Hans Schierling, Project Manager Licensing Branch No. 3 Division of Licensing
SUBJECT:
DIABLO CANYON: MEETING WITH PG&E ON SEISMIC LICENSE C0tlBITION DATE & TIME:
May 8, 1984 8:30 am LOCATION:
Room 1713 Maryland National Bank Building Bethesda, Maryland PURPOSE:
To discuss with PG&E specific elements for revalidation program for seismic design bases in accordance with license condition.
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PAP,TICIPANTS:
NRC R. Jackson, S. Brocoum, L. Reiter, R. McMullen, R. Rothman, H. Schierling, USGS Consultants PG8E J. Hoch, et al.
Orininalsigned by:
Ifans Schlerling Hans Schierling, Pro.iect Manager Licensing Branch No. 3 Division of Licensing cc: See next page l
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DRAFT 4/27/84 PROPOSED AGENDA FOR THE DIABLO CANYON AND EXTREME EXTERNAL PHENOMENA SUBCOMMITTEE MEETINGS ON THURSDAY, MAY 24, 1984 1.
Executive Session C. Siess 15 Min.
- 8:45 am D. Okrent 2.
Status of Licensing Activities NRC Staff 15 Min.
8:45 - 9:00 am on Diablo Canyon i
3.
Discussion of issues raised in April 13,1984 Lettet from N. Palladino to J. Ebersole a) Discussion of proposed siesmic reevaluation
- 1) Discussion of NRC Staff 1 Hr &
9:00 - 10:30 am proposal for a seismic 30 Min.
g reevaluation
- BREAK *=***
15 Min.
10:30 - 10145 am
- 2) Coments from NRC Working 30 Min.
10:45 - 11:15 ac:
Group on Seismic Design Margins
- 3) PG8E Coments 30 Min.
11:15 - 11:45 am
- 4) General Discussion and 60 Min.
11:45 - 12:45 pm ACRS Consultant's Coments
- LUNCH *****
1 Hour 12:45 - 1:45 pm b) Discussion of technical paper by J. Crouch, et al
- 1) Discussion of NRC Staff 30 Min.
1:45 - 2:15 pm Position c-
- 2) USGS Coments 30 Min.
2:15 - 2:45 pm i
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.:2-4/27/84 Diablo Canyon & EEP Agenda
- 3) PG&E Coments 30 Min.
2i45-3:15pm
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15 Min.
3:15 - 3:30 pm
- 4) General Discussion and 60 Min.
3:30 - 4:30 pm
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ACRS Consultants Coments 4.
Sumary, Conclusions and Future C. Siess 30 Min.
I:3b - 5:00 pm Actions D. Okrent Adjourrment 9
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