ML12347A310

Summary of Meeting with Public on Diablo Canyon Power Plant

ML12347A310
Person / Time
Site:	Diablo Canyon
Issue date:	12/12/2012
From:	Thomas Farnholtz Region 4 Engineering Branch 1
To:
References
Download: ML12347A310 (17)

Text

December 12, 2012

SUMMARY

OF OPEN HOUSE AND POSTER SESSION WITH MEMBERS OF THE PUBLIC FACILITY:

Diablo Canyon Power Plant On Wednesday, November 28, 2012, a Category 3 meeting was held between the U.S. Nuclear Regulatory Commission (NRC) and the public at the Embassy Suites, 333 Madonna Road, in San Luis Obispo, California.

The NRC held two poster sessions with information on the recently issued NRC Research Information Letter (RIL), in response to the PG&E report on the Analysis of the Shoreline Fault Zone, the Diablo Canyon Power Plant performance, the Japanese Lessons Learned Project Directorate, and Waste Confidence and License Renewal. Also in attendance was a representative from the California Geological Survey with information on studies conducted by Pacific Gas & Electric. A copy of these posters and their associated handouts can be found in the enclosures. Those documents already available publicly are not enclosed, but reference number is listed.

The poster sessions were followed by a question and answer session, which was recorded. A video of the question and answer session will be posted on the website available at:

http://www.nrc.gov/info-finder/reactor/diab1.html or http://www.nrc.gov/info-finder/reactor/diab2.html.

In accordance with 10 CFR 2.390 of the NRCs Rules of Practice, a copy of this letter and its enclosures will be available electronically for public inspection in the NRCs Public Document Room or from the Publicly Available Records (PARs) component of the NRCs Agency wide Document Access and Management System (ADAMS). ADAMS is accessible from the Public Electronic Reading Room page of the NRCs public web site at:

www.nrc.gov/readingrm/adams.html.

To receive a summary of future meetings and other plant-specific e-mail distributions, you must subscribe to the Operating Reactor Correspondence electronic distribution for this plant via:

www.nrc.gov/public-involve/listserver/plants-by-region.html. Once subscribed, if you wish to discontinue receiving electronic distribution, you may unsubscribe at any time by visiting the same web address listed above.

CONTACT: Tom Farnholtz, RIV/DRS (817) 200-1243 Docket Nos.: 50-275; 50-323 UNITED STATES NUCLEAR REGULATORY COMMISSION REGION IV 1600 EAST LAMAR BLVD ARLINGTON, TEXAS 76011-4511

Diablo Canyon Public Meeting Summary

Enclosures:

Research Information Letter Poster Senior Seismic Hazard Analysis Committee Poster Japanese Lessons Learned Project Directorate Poster Resident Inspectors Poster California Public Utilities Commission Independent Peer Review Panel Poster RIL Executive Summary (ML121230035)

RIL Appendix A (ML121230035)

RIL Trifold Summary RIL Frequently Asked Questions and Answers Diablo Canyon Mid-Cycle Performance Assessment Letter (ML12248A413)

Diablo Canyon Public Meeting Summary Electronic Correspondence:

NRC Attendees Regional Administrator (Elmo.Collins@nrc.gov)

Deputy Regional Administrator (Steven.Reynolds@nrc.gov)

DRP Director (Kriss.Kennedy@nrc.gov)

Acting DRP Deputy Director, Acting (Barry.Westreich@nrc.gov)

Acting DRS Director (Tom.Blount@nrc.gov)

Acting DRS Deputy Director (Jeff.Clark@nrc.gov)

Vince Gaddy, C:DRS/OB (Vincent.Gaddy@nrc.gov)

Sue Bogle (OEWEB Resource) mortensengk@INPO.org Project Engineer, DRP/B (David.You@nrc.gov)

DC Administrative Assistant (Madeleine.Arel-Davis@nrc.gov)

Public Affairs Officer (Victor.Dricks@nrc.gov)

Branch Chief, DRS/TSB (Ray.Kellar@nrc.gov)

RITS Coordinator (Marisa.Herrera@nrc.gov)

Regional Counsel (Karla.Fuller@nrc.gov)

Congressional Affairs Officer (Jenny.Weil@nrc.gov)

OEMail Resource, D/OE Heather Gepford, Region IV ACES (Heather.Gepford@nrc.gov)

Regional State Liaison Officer (Bill.Maier@nrc.gov)

R:\\_REACTORS\\_DC\\2012\\DC MS 12-14-2012.doc SUNSI Rev Compl.

Yes No ADAMS Yes No Reviewer Initials TFR Publicly Avail Yes No Sensitive Yes No Sens. Type Initials TFR RIV/RI:DRS PAO RSLO C:DRS/EB1 MWilliams LUselding WMaier TFarnholtz

/RA/

/RA via email/

/RA via email/

/RA/

12/07/2012 12/07/2012 12/07/2012 12/12/2012 OFFICIAL RECORD COPY T=Telephone E=E-mail F=Fax

Research Information Letter 12-01 Confirmatory Analysis of Seismic Hazard at the Diablo Canyon Power Plant from the Shoreline Fault Zone Shoreline Fault Zone Key References US NRC (2012) Research Information Letter 12-01: Confirmatory Analysis of Seismic Hazard at the Diablo Canyon Power Plant from the Shoreline Fault Zone (ML121230035)

Pacific Gas & Electric Company, Final Report of the Diablo Canyon Long-Term Seismic Program, Report to the U.S. NRC, Agencywide Documents and Access Management System (ADAMS) Accession No. ML8803160246, U.S. Nuclear Regulatory Commission Docket Nos. 50-275 and 50-323, San Francisco, CA, 1988.

Pacific Gas & Electric Company, Report on the Analysis of the Shoreline Fault Zone, Central Coastal California, Report to the U.S. Nuclear Regulatory Commission, ADAMS Accession No. ML110140431, 2011.

Inputs to NRC Deterministic Seismic Hazard Assessment Type of Faulting Shear Wave Velocity of Site Distance from the Rupture Plane to the Site Five NRC Faulting Scenarios for the Shoreline Fault The NRC developed five upper bound scenarios to characterize the possible Shoreline fault ground motions based on the available data. The NRC then performed a Deterministic Seismic Hazard Assessment (DSHA) considering two scenario earthquakes: a M5.9 earthquake, representing Scenario 1, and a M6.7 earthquake, representing Scenarios 3 and 4. Scenario 1, which characterizes the Shoreline fault as a creeping fault, is an interpretation that is consistent with the available geologic and seismic data. The NRC staff considers the M6.7 scenarios to yield a reasonable maximum magnitude based on an appropriately conservative interpretation of all available information.

 Identified in November 2008 during collaborative research between Pacific Gas and Electric (PG&E) and the U.S. Geological Survey (USGS)

 Approximately 600 meters from the reactor and 300 meters offshore

 The NRCs first assessment of the Shoreline fault was detailed in RIL 09-001. RIL 12-01 updates the NRCs evaluation based on information PG&E provided in January 2011, as well as a staff visit to Diablo Canyon Scenario Scenario Description Mmax 1

Shoreline fault is aseismic and creeping with a slow slip rate.



2 Shoreline fault extends 16 km from its intersection with the Hosgri fault south-southeast to where the fault is truncated by the San Luis Bay system of faults.

6.4 - 6.5 3

Shoreline fault extends 15 km from its intersections with the Hosgri fault south-southeast to where the fault merges with the 8-km-long eastern portion of the San Luis Bay fault, for a total length of 23 km.

6.5 - 6.7 4

Shoreline fault extends 23 km and includes all three of the mapped segments (north, central, and south) as mapped by PG&E in the Shoreline Fault Report (PG&E, 2011).

6.5 - 6.7 5

Shoreline fault includes the entire length of the fault as mapped by PG&E (2011), plus additional rupture farther to the southeast another 10 km for a total fault length of 33 km.

6.7 - 6.9 Results from NRC Deterministic Seismic Hazard Assessment The ground motion spectra resulting from the NRC staffs DSHA are at or below the HE and LTSP ground motion spectra for which the plant was evaluated previously and demonstrated to have reasonable assurance of safety. Therefore, the Shoreline fault, as characterized by the NRC review, does not challenge the current licensing basis.

Input Parameter Parameter Values Used in This Study Ground Motion Prediction Equations (GMPEs)

Abrahamson & Silva (2008), Boore & Atkinson (2008), Campbell & Bozorgnia (2008), Chiou &

Youngs (2008), and Graizer & Kalkan (2009)

Scenario Maximum Magnitude Magnitudes 5.9 and 6.7 were analyzed Distance From Rupture Plane to Site 600 meters Type of Faulting Strike Slip Near-Surface Shear Wave Velocity of Site Best estimate of 1,200 m/s Depth to Hard Rock Conditions 0 km to Vs = 1.0 km/s, 2 km to Vs = 2.5 km/s Dip Angle of Fault Plane No dip (vertical strike slip fault)

Depth to Rupture 0 km (surface rupture assumed)

Comparison of 2010 DCPP Independent Spent Fuel Storage Installation (ISFSI) velocity profiles to that of the 1978 velocity profile.

Focal mechanisms recorded in the vicinity of DCPP Comparison of results of 84th-percentile ground motions for magnitude 5.9 and 6.7 earthquakes on the Shoreline fault to Hosgri and LTSP ground motion response spectra.

Next Steps PG&E is currently performing a Probabilistic Seismic Hazard Assessment (PSHA) for DCPP using the Senior Seismic Hazard Analysis Committee (SSHAC) Level 3 process endorsed by the NRC and described in NUREG 2117 and NUREG/CR-6372. The updated seismic hazard information developed through the SSHAC study will be used by PG&E to respond to the NRCs 10 CFR 50.54(f) Request for Information Letter for post-Fukushima actions.

SSHAC Process (Senior Seismic Hazard Analysis Committee)

Objective The complexity of tectonic environments, coupled with the limitations in the data available for seismic source characterization (SSC) and ground motion characterization (GMC) make the use of a significant level of expert judgment in seismic hazard assessment studies unavoidable. For critical facilities such as nuclear power plants, the judgments of multiple experts are required to capture the complete distribution of technically defensible interpretations (TDIs) of the available earth science data. The Senior Seismic Hazard Analysis Committee (SSHAC) process provides a transparent method of structured expert interaction entirely focused on capturing the center, body, and range (CBR) of the full suite of TDIs that the available data permit. The SSHAC process results in a logic tree model and supporting documentation developed by the TI team and reviewed by the PPRP. NRC NUREG 2117 provides recently published practical guidance on performing a SSHAC study.

Key References U.S. Nuclear Regulatory Commission, Recommendations for Probabilistic Seismic Hazard Analysis: Guidance on Uncertainty and Use of Experts, NUREG/CR-6372, Washington, DC, 1997.

U.S. Nuclear Regulatory Commission, A Performance-Based Approach to Define the Site-Specific Earthquake Ground Motion, Regulatory Guide 1.208, Washington, DC, March 2007.

U.S. Nuclear Regulatory Commission, Practical Implementation Guidelines for SSHAC Level 3 and 4 Hazard Studies, NUREG-2117, Washington, DC, 2012.

Overview of a Level 3 Process Participants Meeting the objectives of the SSHAC process requires participants to fill a number of very precisely defined roles.

Some participants are involved throughout the process, while others come in the address specific needs. These roles include:

Technical Integrator (TI)

Construct a model for input to a probabilistic seismic hazard analysis (PSHA) that captures the CBR of the TDI and provide complete and clear justifications of the technical bases for all elements of the model.

Participatory Peer Review Panel (PPRP) Member Provide clear and timely feedback to the project to ensure that any technical or process deficiencies are identified and corrected at the earliest possible stage.

Resource Expert Present data, models, and methods in an impartial manner.

Proponent Expert Advocate a specific model, method, or parameter for use in the hazard analysis.

Evaluator Expert Identify and objectively examine available data and diverse models, challenge their technical bases and



  











models against observations.

Workshops Workshops are a critical part of the SSHAC process. A minimum of three workshops, each with a specific focus and objective, are required.

Workshop 1: Significant Issues and Available Data 1.

identify the technical issues of highest significance to the hazard analysis 2.

identify the available data and information that will be needed to address those issues Workshop 2: Alternative Interpretations 1.

present, discuss, and debate alternative viewpoints on key technical issues 2.

identify the technical bases for the alternative hypotheses and to discuss the associated uncertainties 3.

provide a basis for the subsequent development of preliminary hazard models that consider these alternative viewpoints Workshop 3: Feedback 1.

present and discuss the preliminary models, hazard input documents (HID), and calculations in a forum that provides the opportunity for feedback to the evaluators Documentation The project documentation must be clear and complete so that the reader can understand:

1. what process was used in the hazard analysis

2. what data were available and used in the evaluation process

3. how the data, models, and methods of the larger technical community were considered

4. the elements of the models and their technical bases

5. how the models capture the CBR of TDIs

6. the hazard results and instructions for their use

Learning from Fukushima: The NRCs Past, Present, and Future Actions Three-Tiered Prioritization of Actions Timeline: Major NRC Actions Future Milestone Actions Tier 1 Orders issued March 12, 2012

• Develop strategies to mitigate beyond design basis external events.

• Install reliable hardened vents in boiling water reactors with Mark I and II containments.

• Install enhanced spent fuel pool level instrumentation.

Request For Information under 10 CFR 50.54(f) issued March 12, 2012

• Reevaluate seismic and flooding hazards.

• Perform walkdowns of seismic and flooding hazards.

• Assess staffing and communications equipment needs to respond to multiunit events and prolonged station blackout (SBO).

Rulemaking Initiatives

• Modify the SBO rule to enhance SBO mitigation capability.

• Strengthen and integrate onsite emergency response procedures, training, and exercises.

Tier 2

• Enhance spent fuel pool makeup capability.

• Take additional emergency preparedness (EP) regulatory actions.

Tier 3

• Periodically confirm seismic and flooding hazard assumptions.

• Evaluate potential enhancements for preventing or mitigating seismically-induced fires and floods.

• Evaluate the need for reliable hardened vents in other containment designs.

• Assess the need for hydrogen control and mitigation inside containment and other buildings.

• Make additional Emergency Preparedness enhancements to address prolonged SBO and multiunit events.

• Evaluate the need to enhance Emergency Response Data System capability.

• Modify the Reactor Oversight Process to reflect revised defense in depth framework.

• Enhance NRC staff training on severe accidents and SAMGs.

• Confirm basis of emergency planning zone size.

• Evaluate the need for prestaging of potassium iodide beyond 10 miles.

• Evaluate merits of transferring spent fuel to dry cask storage.

NRC Oversight of Licensee Implementation

• Review licensee submittals.

• Document results of review.

• Take further regulatory action if warranted.

• Conduct inspections to verify compliance with requirements and commitments.

May 31, 2012 The NRC issued guidance for conducting the seismic and flooding walkdowns.

November 2012 The NRC expects to receive the results of seismic and flooding walkdowns from every operating reactor.

March 12, 2012, The NRC issued three regulatory orders and a request for information to licensees.

November 2012 The NRC expects to issue guidance related to the seismic and flooding hazard reevaluations.

April 29, 2011, Temporary Instruction (TI) 2515/184 The NRC gave guidance to its inspectors to assess the state of severe accident management guidelines (SAMGs) at U.S. facilities.

March 11, 2011 A magnitude 9.0 earthquake struck near Honshu, Japan, generating an estimated 45-foot tsunami at the Fukushima Daiichi site.

July 13, 2012SECY-12-0095 The NRC issued program plans that lay out an approach for addressing each Tier 3 recommendation.

May 11, 2011, NRC Bulletin 2011-01 The NRC required licensees to verify compliance with Title 10 of the Code of Federal Regulations (10 CFR) 50.54(hh)(2) and respond with information about their mitigating strategies programs.

October 3, 2011, SECY-11-0137 NRC staff proposed to the Commission a three tier prioritization of the NTTF recommendations.

Spring 2016 Diablo Canyon expected to achieve full implementation of the Tier 1 orders.

May 14, 2012 The NRC issued guidance for completion of the communication and staffing assessments.

February 2013 The NRC expects to receive site-specific integrated plans from each licensee for implementation of Tier 1 orders.

March 23, 2011, Temporary Instruction (TI) 2515/183 The NRC gave guidance to its inspectors to assess the adequacy of actions U.S.

licensees have taken in response to the Fukushima accident.

July 12, 2011, Near-Term Task Force (NTTF) Review of Insights from the Fukushima Dai-ichi Accident SECY-11-0093 The NTTF issued a report with 12 recommendations for enhancing reactor safety.

May 11, 2012 The NRC issued a letter to all licensees prioritizing the completion dates for the flooding reevaluations at each reactor site.

August 29, 2012 The NRC issued or endorsed implementation guidance for each of the three Tier 1 orders.

March 12, 2015 Diablo Canyons seismic and flooding hazard reevaluations are due to the NRC.

This will determine if additional actions are needed.

THE NEA R-TERM TA SK FORCE REVIEW OF INSIGHTS FROM THE FUKUSHIMA DAI-ICHI ACCIDENT

I n d e p e n d e n t P e e r R e v i e w P a n e l e v a l u a t i o n o f p r o p o s e d s e i s m i c h a z a r d s t u d i e s a t D i a b l o C a n y o n Assembly Bill (AB) 1632 (Blakeslee, 2006) directed the California Energy Commission (CEC) to assess the potential vulnerability of Californias largest baseload power plants to a major disruption due to a major seismic event and other issues.

In response to AB 1632, the CEC issued its findings and recommendations in its AB 1632 Report.

The CEC AB1632 report (2008) recommended that PG&E should use three-dimensional geophysical seismic reflection mapping and other advanced techniques to explore fault zones near Diablo Canyon The California Public Utilities Commission has convened its own Independent Peer Review Panel (IPRP) and invited the CEC, the California Geologic Survey, the California Coastal Commission, the California Seismic Safety Commission the California Emergency Management Agency and the County of San Luis Obispo to participate on the panel. The IPRP is conducting an independent review of PG&Es on-shore and off-shore seismic studies including independently reviewing and commenting on PG&Es study plans and findings. The IPRPs goal is to provide recommendations for studies to further refine our understanding of the potential seismic hazard at DCPP.

I n d e p e n d e n t P e e r R e v i e w P a n e l A multi-agency panel of seismic hazard specialists established by the California Public Utilities Commission CALIFORNIA GEOLOGICAL SURVEY, CALIFORNIA COASTAL COMMISSION CALIFORNIA EMERGENCY MANAGEMENT AGENCY, CALIFORNIA ENERGY COMMISSION CALIFORNIA SEISMIC SAFETY COMMISSION, CALIFORNIA PUBLIC UTILITIES COMMISSION COUNTY OF SAN LUIS OBISPO Object of study PG&E Study Plans IPRP Evaluation of PG&E Study Plans Priority HHoossggrrii FFaauulltt SSlliipp RRaattee LLooww EEnneerrggyy 33--DD SSeeiissm miicc SSuurrvveeyy The IPRP recommends further studies to decrease the uncertainty in the seismic hazard at Diablo Canyon by better constraining the slip rate on the Hosgri Fault.

High LLooss O Ossooss FFaauulltt DDiipp HHiigghh EEnneerrggyy oonn--llaanndd 22--DD SSeeiissm miicc SSuurrvveeyy The current plans for on-land seismic surveys appear to be adequate to image reverse faults beneath the hills. The IPRP will be interested in reviewing the results that show the Los Osos Fault, but also any other geologic structure or structures beneath the hills.

High, Awaiting results of surveys in 2011 LLooss O Ossooss SSeennssee ooff SSlliipp LLooss O Ossooss SSlliipp RRaattee The IPRP believes that a broader goal of the on-land seismic surveys should be for PG&E to develop a tectonic model of the Irish Hills that includes defining the locations and slip rates on all faults beneath the hills that can be checked against rates of uplift and surface deformation.

High, Awaiting results of surveys in 2011 SShhoorreelliinnee FFaauulltt SSlliipp RRaattee LLooww EEnneerrggyy 33--DD SSeeiissm miicc SSuurrvveeyy The IPRP recommends further studies to decrease the uncertainty in the seismic hazard at Diablo Canyon by better constraining the slip rate on the Shoreline Fault.

High Southeast End of Shoreline Fault This type of study has as good a chance as currently feasible of providing data on the orientation and continuity of the southeast end of the Shoreline Fault. The IPRP recommends that a secondary focus of these studies should be to constrain any potential connections to faults on-shore.

Moderate Hosgri -

Shoreline Intersection High Energy 3-D Seismic Survey This type of study has as good a chance as currently feasible of providing data on the intersection of the Hosgri and Shoreline Faults.

On hold Hosgri Dip This type of study has as good a chance as currently feasible of providing data on the dip the Hosgri Fault near the intersection of the Shoreline and the Hosgri Faults.

On hold Shoreline Fault Segments This type of study has as good a chance as currently feasible of providing data on the orientation and continuity of the Shoreline Fault at depth On hold Hosgri-San Simeon Step-Over Ongoing investigation and more closely spaced seismic survey lines by USGS have shown that the direct connection between the San Simeon and Hosgri Faults is by far the most likely explanation from the available data. It appears very unlikely that additional data from high energy survey of this area would significantly change the seismic hazard analysis results based on these faults.

No longer proposed

RIL 09-001



The NRCs first assessment of the Shoreline fault was detailed in RIL 09-001 and was based on information available at the time. The NRC found the Shoreline faults maximum predicted shaking is less than what the plant was previously analyzed for.

RIL 12-001



RIL 12-01, Confirmatory Analysis of Seismic Hazard at the Diablo Canyon Power Plant from the Shoreline Fault Zone, updates the NRCs evaluation based on information PG&E provided in January 2011, as well as a staff visit to Diablo Canyon.



The NRC continues to conclude that ground shaking from the Shoreline faults earthquake scenarios are less than the HE and LTSP ground motion levels for which the plant was previously evaluated and demonstrated to have reasonable assurance of safety Comparison of Hosgri and LTSP Spectra to NRC Deterministic Evaluation Results JAPAN LESSONS LEARNED



The NRC staff issued a request for additional information to all nuclear power plants on March 12, 2012, to initiate several actions as a result of lessons learned from the Fukushima Dai-ichi accident in Japan:

 Conduct walkdowns of all nuclear power plants to verify flooding and seismic protection features

 Reevaluate flooding and seismic hazard and design using present day methods and guidance

 The DCPP seismic hazard reevaluation, scheduled to be submitted by March 2015, will assess all known faults in the area (i.e., not limited to just the Shoreline fault) using a process similar to what is done for siting new reactors.

For additional information contact the Office of Public Affairs. Phone: (301) 415-8200 or email: opa@nrc.gov NRC REVIEW OF SEISMIC HAZARD AT THE DIABLO CANYON POWER PLANT FROM THE SHORELINE FAULT ZONE This brochure provides an overview of the NRCs review of the Shoreline fault zone near Diablo Canyon. It also places the Shoreline fault review in context with the NRCs request that all U.S. nuclear power plants reanalyze seismic hazards based on lessons learned from the Fukushima Dai-ichi accident in Japan.

(Prepared November 2012)

DIABLO CANYON POWER PLANT SEISMIC BACKGROUND



Nuclear power plant designs consider earthquake effects by providing margins against ground motion levels at the plant site.



The ground motion levels show how much energy (measured in g, or percent of Earths gravity) is transmitted at different shaking frequencies



Designers use ground motion levels to analyze how structures and equipment respond during an earthquake



Diablo Canyon is licensed to three earthquake ground motions (most plants have two)



Design Earthquake (DE) ground motion is the biggest earthquake the plant is allowed to continue operating through

 The DE ground motion level is 0.2g anchored at 100 Hz



Double Design Earthquake (DDE),

ground motion is the shaking level at which all safety related equipment must remain functional

 The DDE ground motion level is double the amplitude of the DE (0.4g peak ground acceleration anchored at 100 Hz)



Hosgri Earthquake (HE) ground motion level, which is based on an earthquake from the Hosgri fault, which was discovered in 1971.

 The HE ground motion level is 0.75g peak ground acceleration anchored at 100 Hz based on a 7.5 magnitude earthquake 5 kilometers from the site

 Diablo Canyons design was modified so that sufficient equipment survives the HE to safely shutdown the plant and keep the nuclear fuel cool



Long Term Seismic Program (LTSP)



The plants original license required seismic reevaluation in 10 years



The LTSP was initiated to meet this license condition



The LTSP spectrum has been used to evaluate seismic margins SHORELINE FAULT



In November of 2008, plant owner Pacific Gas and Electric (PG&E) informed the NRC it had identified a previously unknown fault during collaborative research with the U.S.

Geological Survey (USGS)



The Shoreline fault is approximately 600 meters from the reactor and 300 meters offshore



The NRCs first assessment of the Shoreline fault was detailed in Research Information Letter (RIL)09-001, Preliminary Deterministic Analysis of Seismic Hazard at Diablo Canyon Nuclear Power Plant from Newly Identified Shoreline Fault

QUESTIONS AND ANSWERS ASSOCIATED WITH ISSUANCE OF RESEARCH INFORMATION LETTER RELATED TO SEISMIC HAZARD AT THE DIABLO CANYON POWER PLANT FROM THE SHORELINE FAULT ZONE

1.

How was the Shoreline fault found?

The Shoreline fault was discovered while re-analyzing existing earthquake data gathered as part of a research program being conducted by PG&E and the USGS to better understand the seismology of the central California coastal region. This effort is being conducted through a Collaborative Research and Development Agreement (CRADA).

2.

How long has this research being ongoing?

The CRADA is a long-standing research program. The current phase of the CRADA was initiated in 2007 and has been has been ongoing since then.

Seismic research related to the Diablo Canyon site has been ongoing since the late 1960s.

3.

Where exactly is the fault?

It is mapped approximately 600 meters offshore west of the Diablo Canyon Power Plant (DCPP), trending NW-SE, nearly parallel to the coastline.

4.

When was the NRC notified of the new fault?

The licensee notified onsite inspectors of the fault on November 14, 2008.

5.

Has the fault been completely characterized?

PG&E and the USGS continue to evaluate the fault through both field investigations and analyses as part of the SSHAC Level 3 study. However, a characterization of the fault was provided by PG&E in January of 2011. Both the staffs assessment of the analyses in the PG&E report and the NRC staffs own independent evaluation are provided in the RIL. A more detailed probabilistic assessment of all faults with the potential to impact the DCPP is currently being performed in accordance with a March 12, 2012, letter from the NRC. This more detailed assessment is expected to take 3 years to complete. PG&E is also working to complete a series of detailed two and three-dimensional seismic surveys to illuminate the faults in the subsurface beneath the DCPP.

6.

What effect does the new fault have on seismic risk at DCPP?

Based on current information, the new fault has a minimal effect on the risk to DCPP. Although close to the DCPP, the Shoreline fault does not appear to be capable of generating ground motions that could damage the DCPP. The results of the evaluations by the licensee and the independent study by the NRC indicate that ground shaking at the plant site that could result from earthquakes on the Shoreline fault are bounded by the larger ground motions that could result at the plant site from earthquakes on the Hosgri fault. The plant has been

evaluated previously and demonstrated to have reasonable assurance of safety under the ground motions that could be produced by the Hosgri fault. The micro-earthquakes that were used to identify the Shoreline fault were already part of the existing seismologic database.

Because the Shoreline fault is approximately 600 meters from DCPP, and much closer to the DCPP than the Hosgri fault, PG&E and the NRC also evaluated the potential for surface fault displacements on the Shoreline fault to impact the structures, systems, and components (SSCs) of the DCPP. Although fault slip on the Shoreline fault itself cannot impact the DCPP, such fault displacements may cause secondary deformations in the near field of the fault trace. The potential impact of secondary ground deformation primarily involves the buried components, such as piping and conduits. Both the PG&E and NRC analyses indicate that the risk to the DCPP from secondary ground deformations is insignificant even when making highly conservative assumptions. The analyses performed by NRC staff are described in the RIL. There is no geologic evidence that the Shoreline fault has produced surface fault rupture on land.

Based on these analyses of ground motions and fault displacements therefore, the Shoreline fault does not pose a new safety hazard to the DCPP.

7.

What is the Hosgri Fault?

The Hosgri fault is a NW-SE trending strike-slip fault located offshore 5 km to the west of the DCPP. Based on the maximum magnitude earthquake that could occur on the Hosgri fault, seismologists determined that it is capable of generating ground motions up to 0.75g (peak ground acceleration) at the DCPP site. The level of ground shaking that the Hosgri fault could generate at the DCPP was the focus of considerable debate and study throughout the original licensing of the DCPP. During an extensive 10 year scientific study call the Long Term Seismic Program (LTSP) conducted after the DCPP was licensed by the NRC, PG&E confirmed the seismic adequacy of plants original design, and showed that SSCs important to safety can withstand the effects of the 0.75g Hosgri ground motions. The LTSP also confirmed that the earlier 0.75g ground motion estimate for the Hosgri fault was still appropriate using the most up to date tools at the time. The current licensing basis for the DCPP is the original design basis ground motions (i.e., the Design Earthquake (DE) and Double Design Earthquake (DDE) ground motions) plus the Hosgri Earthquake (HE) ground motion.

8.

Is it safe for DCPP to continue to operate given the discovery of the Shoreline fault?

Yes, both the licensees evaluation and the NRCs independent evaluation in the RIL concluded that the ground shaking at the DCPP site from the maximum magnitude earthquake that could occur on the Shoreline fault are less than the 0.75g Hosgri ground motions, to which the plant has been evaluated previously and demonstrated to have reasonable assurance of safety.

Additionally, to ensure public health and safety, DCPP has an automatic seismic reactor trip set point of 0.35g. If the ground acceleration at the DCPP from any

earthquake exceeds this 0.35g set point, both reactors will automatically shut down to maintain plant safety and the health and safety of the public.

9.

Is PG&E still assessing seismic information?

Yes, as discussed in the prior Q&As, PG&E continues to collect and assess new seismic information, including work done within the CRADA as part of its long term seismic program. In addition to the field studies and data analyses, PG&E is also conducting a SSHAC Level 3 PSHA study. The updated seismic hazard results from the SSHAC study will be used to respond to the NRC staffs March 12, 2012, Request for Information Pursuant to Title 10 of the Code of Federal Regulations 50.54(f) Regarding Recommendations 2.1, 2.3, and 9.3, of the Near-Term Task Force Review of Insights from the Fukushima Dai-Ichi Accident.

10.

What is the timeframe for PG&E to respond to the NRCs March 12, 2012, request for information?

The current time frames are as follows:

ITEM Milestone Seismic Hazard Update Using Senior Seismic Hazard Analysis Committee (SSHAC) Level 3 Methodology Process completed in 2015 Risk evaluation in accordance with seismic margins assessment or seismic probabilistic risk assessment as appropriate Process completed in 2017 NRC determination of whether additional regulatory actions are necessary based on the results of the above 2017

11.

Given that it may take 5 years for PG&E to completely respond to the NRCs March 12, 2012, letter, why is the plant safe to operate today?

As described in the answer to question 8, the staffs independent evaluation of the data currently available indicates that the ground motion calculated for the Shoreline fault is bounded by the current Hosgri ground motion, to which the plant has been evaluated previously and demonstrated to have reasonable assurance of safety. The data collected and reviewed to date do not indicate any significant changes to the overall hazard at the site.

As outlined in the March 12, 2012, request for information, there is a process for PG&E to provide interim evaluations and actions may be taken if higher seismic hazards relative to the design basis are determined to exist based on the seismic hazard update currently being performed by PG&E. These evaluations are to be provided to the NRC prior to the risk evaluations being performed (i.e., within 3 years).

Lastly, the NRC also continues to monitor the information that PG&E is collecting and will reassess the situation should new information suggests that the faults around Diablo Canyon Power Plant are capable of producing earthquakes and ground motions larger than the current ground motions for which the plant has been evaluated previously and demonstrated to have reasonable assurance of safety.

12.

Why was the Shoreline fault referred to in some documents as a potential fault?

When the zone of seismicity was first discovered in 2008 it was not clear at the time whether or not this zone was a fault and it was therefore characterized as a potential fault. Subsequent to its discovery the United States Geological Survey has described this zone of seismicity as a fault. Therefore, in current NRC documents when describing this zone of seismicity the NRC has removed the term potential and simply refers to this zone as the Shoreline fault.

13.

Will outside experts be involved in assessing the probabilistic seismic hazards?

Yes, experts outside the NRC and PG&E will be involved in the probabilistic seismic hazard assessment. PG&E will use a range of experts to conduct its updated PSHA following the guidance in NUREG/CR-6372 (NRC, 1997) and NUREG 2117 (NRC, 2012). The external experts will be drawn from private consulting companies, State and US government agencies (including the USGS),

and leading academic institutions. These experts will fill a variety of roles (described further in NUREG 2117 and in Appendix A of the RIL). Some may act as formal members of the SSHAC Technical Integration (TI) teams. Others may be tapped as Resource Experts, who act as unbiased experts on a particular database or topic, or as Proponent Experts, who are asked to provide their own judgments on the seismic sources or ground motion modeling that will constitute the updated PG&E PSHA. Still other outside experts will sit on the Participatory Peer Review Team, the formal peer review group for a SSHAC-based study.

NRC experts and their consultants will act as observers to the program in the workshops and open meetings.

14.

Did the NRC evaluate the impact of the Shoreline fault on the Diablo Canyon ISFSI?

Not directly, but by extension, because the licensing basis for the ISFSI was the same set of ground motions that constitute the current seismic qualification basis for the DCPP. In addition, the ISFSI site is underlain by the same ground and soil conditions at the DCPP. Thus, because possible ground motions from a maximum earthquake on the Shoreline fault are less than the ground motions that make up the current seismic qualification basis for the DCPP and the ISFSI, the NRC staff concluded that the new information on the Shoreline fault does not challenge the existing licensing basis for the ISFSI. The NRC staff remain confident that the existing ISFSI is adequately protective of public health and safety and the environment.

15.

Are the results of the SSHAC Level 3 process expected to show that the plant could be subjected to higher ground motion than it was designed to withstand?

Based on current information, NRC staff does not expect the updated PG&E PSHA to indicate higher ground motions than those to which the plant has been designed. This is because one of the key advancements in earthquake seismology in recent years has been the improved ground motion prediction equations (GMPEs, formerly called attenuation models) that were developed from the Pacific Earthquake and Engineering Research (PEER) Centers Next

Generation Attenuation (NGA) project. For most earthquake scenarios of interest to the DCPP, these new GMPEs predict lower amplitudes of ground motions at the site than those used to develop the ground motions that constitute the current licensing basis. As noted in the answer to question 11, the NRC is prepared to reassess the situation should it discover that the new information shows that the faults around Diablo Canyon Power Plant are capable of producing ground motions larger than the current ground motions for which the plant has been evaluated previously and demonstrated to have reasonable assurance of safety.

16.

Why doesnt the RIL address the possibility that the Shoreline fault might rupture another close fault, creating a larger fault with higher ground motion?

The RIL does address this possibility. The RIL describes the NRC staffs assessment and proves the basis for the staffs findings. A multi-fault rupture would, necessarily, be a large magnitude earthquake, which would leave evidence in the landscape. However, the data available indicates that there has not been surface rupture at the location of the shoreline fault and there is no visible relative displacement across the fault.

There is no geologic, geophysical, or seismological evidence that past earthquakes on the Shoreline fault or other faults around the DCPP have triggered rupture on any of the small faults near the DCPP. The exposed faults in the Discharge and Intake coves were examined by PG&E and the NRC review team, and both reviews concluded that fault slip on these faults appear to be geologically older structures not related to the present seismo-tectonic stresses affecting the DCPP site. Additionally, both PG&E and the NRC performed probabilistic studies to assess the potential for secondary deformation resulting from a rupture on the Shoreline fault and found the risk to the DCPP to be negligible.

17.

Why does the NRC use the 84th percentile seismic loading levels to review deterministic seismic evaluations instead of the 95th or 98th percentiles?

Use of the 84th percentile has been the state of practice for deterministic analyes for decades. Statistically, the 84th percentile is the average value plus one standard deviation. NRC considers the 84th percentile to provide a reasonable level of conservatism in the analysis and one that has been applied over many years of NRC seismic hazards and seismic risk assessments. The 84th percentile ground motion is also consistent with the current licensing basis of the DCPP.

Additional Questions Associated with the March 12, 2012, Request for Additional Information in Accordance with 10 CFR 50.54(f) and How it Relates to the Diablo Seismic Review -

Site specific Supplement to 50.54(f) Generic Communication Plan

18.

The recent 50.54f letters ask licensees to do a SSHAC level 3. External stakeholder question "why not level 4?"

As noted in NUREG 2117, the NRC considers Level 3 and level 4 SSHAC studies to be equally valid options from a regulatory perspective. Either a

SSHAC level 3 or 4 could be used to meet the 50.54(f) letter request. A level 4 study is not better than a level 3 study. Rather the appropriate choice of study level is based on a variety of considerations, as discussed in Section 4.2 of NUREG 2117. In both cases the goal is to develop a model that represents the center, body and range of technically defensible interpretations; that is a model that provides both a best estimate ground motion and a robust estimate of the uncertainty.

The main differences between level 3 and level 4 SSHAC study is the framework and composition of the team or teams that develop the PSHA logic tree. In a Level 3 process, the PSHA model is developed by one large Technical Integration (TI) team, which is sometimes broken into source characterization and ground motion characterization sub-project teams. During the formal evaluation and integration processes (as described in NUREG 2117), TI team members are expected to continually engage in challenge and discussion among team members such that a robust model that meets the goal is developed. In a Level 4 process, models in the form of logic tress are developed by several small model development teams of experts and the models are then combined by a technical facilitator integrator (TFI) who is expected to encourage and challenge the experts, and if needed, to orchestrate complex integration among the experts. Because of the differences in approach, in a SSHAC Level 3 study, the PPRP has a stronger role and provides both technical and process oversight. In a Level 4 study, the PPRP only reviews the process. Level 3 and 4 studies each have their benefits and drawbacks. However, in the case of studies to address the 50.54(f) letter, the benefits of a Level 3 study are significant.

19.

Is there a way of integrating and coordinating among the SSHAC PSHA and the States Independent Peer Review Panel (IPRP)?

As described in NUREG/CR-6372 and NUREG 2117, the SSHAC process is a structured formal expert interaction process designed to develop a model that captures the center, body and range of technically defensible interpretations. In order to achieve this, specific and highly defined activities and roles are required.

Within the SSHAC process, the only peer review panel that has formal standing is the projects Participatory Peer Review Panel (PPRP). All other reviewers, including the States IPRP and the NRC review team are observers.. It is anticipated that both the IPRP and the NRCs review team will observe the processes and provide input during the workshops at the times set aside for observer input. An example of the participation of an important outside group as observers is the USGS participation in the the Central and Eastern US Seismic Source Characterization for Nuclear Facilities Project. The USGS as an agency provided a review, which was considered by the project Technical Integration team, the PPRP, and the NRC during its sponsor review. However, only the PPRPs review and acceptance was required for project completion. In considering the acceptability of the SSHAC Level 3 studies that will be submitted in response to the 50.54(f) process, the level of PPRP review and the adherence to the SSHAC process will be fundamental review elements for the NRC. NRC staff and consultants will observe the SSHAC workshops and will provide feedback immediately at the workshops if issues or concerns arise; the IPRP is encouraged to also provide such feedback.

20.

Does the PG&E SSHAC Level 3 project get any input from or participation by the USGS?

Yes, the USGS is involved in the PSHA SSHAC process in several important ways. First, at the first PG&E SSHAC PSHA workshop several USGS geologists, geophysicists, and seismologists were present and made presentations as resource experts. The role of resource experts is to provide in-depth unbiased information on data, models or methods, as discussed in section 3.6.1 of NUREG 2117. Second, several USGS geologists, geophysicists, and seismologists will likely participate in the second SSHAC workshop as proponent experts. The role of proponent experts is to promote the adoption of a particular model or interpretation and to defend a particular model or interpretation against challenge at the SSHAC workshop focused on discussion of proponent models (workshop#2) described in section 3.6.2 of NUREG 2117. Lastly, the SSHAC process makes extensive use of USGS data and models.

21.

PG&E's January 2011 Shoreline report provided an updated probabilistic seismic hazards analysis that included a discussion of other faults (e.g., San Luis Bay and Los Osos faults). Does the RIL address these faults in addition to the shoreline fault?

The RIL does not provide an evaluation of PG&E's updated PSHA, but does provide a limited review of the information provided relative to other faults.

Based on the information provided, none of the faults in the region is capable of challenging the DCPPs licensing basis. All of the regional faults of interest will be evaluated and characterized in the SSHAC Level 3 project currently ongoing.

The purpose of the RIL was to document the NRC's staff's independent deterministic evaluation of the Shoreline fault. However, in the Chapter 6 of the RIL, NRC summarizes some of the basic components of a PSHA and with an emphasis on geological and tectonic factors that are important to fault slip rates.

Fault slip rate is not considered in a deterministic analysis, but is critical to understanding which faults contribute most to a seismic hazard in probabilistic assessments. The discussion found in Chapter 6 and appendix A of the RIL also discusses the process used to develop a PSHA from the Senior Seismic Hazard Analysis Committee (SSHAC) process. The use of PSHA is also consistent with the March 12, 2012 request for additional information provided to all operating power plants pursuant to 10 CFR 50.54(f).

Chapter 6 of the RIL notes that although the staff did not evaluate the PSHA, which will be updated based on information being collected to respond to the March 12, 2012 letter, that the staffs deterministic study does provide several insights; namely that the Shoreline fault is not a major contributor to the seismic hazard at DCPP and that the Hosgri fault remains a dominant seismic source.

Additional Questions Associated with Three Dimensional High Energy Seismic Surveys

22. Is it an NRC requirement that the 3D high energy offshore seismic surveys be performed?

No, it is not identified as a specific data need in the March 12, 2012 request for information issued pursuant to 10 CFR 50.54(f). However, if the surveys are performed they could be used as part of the dataset used to develop the response to the March 12, 2012 request for information.

The 3D high energy offshore surveys are being performed in response to a California State law.1 The 3D seismic studies would be part of a much larger set of information that has been accumulated through and extensive program of onshore and offshore geologic, geophysical and seismic studies. These studies were initiated prior to the Fukushima Da-ichi accident that is the basis for the NRCs March 12, 2012, request for information.

The NRCs March 12, 2012 letter requests seismic reevaluations at the four western U.S plants to be conducted using a SSHAC level 3 or level 4 process to develop a new probabilistic seismic hazard assessment (PSHA) model. The SSHAC process is discussed in NUREG 2117, Practical Implementation Guidelines for SSHAC Level 3 and 4 Hazard Studies, and is summarized in Appendix A of the RIL. In accordance with the SSHAC process, the Technical Integration (TI) Team will perform a thorough assessment of the existing data sets and consider resource expert input to determine the degree to which the 3D high energy offshore survey information is beneficial to development of the PSHA model used to respond to the March 12, 2012 request for information. The TI Team assessment will be reviewed by the SSHAC Peer Review team. If the SSHAC TI Team determines the information is sufficiently complete without the new 3D high energy data to respond to the March 12, 2012 request for information, the DCPP may still be obligated to perform the surveys as part of the commitments made to comply with the California 1 The discussion of the California law can be found in Chapter 1 of the California State Lands Commission Final Environmental Impact Report on the Central Coastal California Seismic Imaging Project which is available at http://www.slc.ca.gov/Division_Pages/DEPM/DEPM_Programs_and_Reports/CCCSIP/CCCSIP.html.

The discussion that follows is paraphrased from this report. California Assembly Bill (AB)1632, directs the California Energy Commission (CEC) to assess the vulnerability of Californias operating nuclear power plants to a major disruption due to a major seismic event or plant aging, the potential impacts of such a disruption, potential impacts from the accumulation of nuclear waste at the State of Californias existing nuclear plants, and other key policy and planning issues regarding the future role of Californias existing nuclear plants. The CEC conducted a comprehensive assessment of Diablo Canyon Power Plant and San Onofre Nuclear Generating Station as directed by AB 1632, and adopted this assessment in November 2008 (2008 Integrated Energy Policy Report (IEPR). The IEPR found that an extended shutdown at either plant would have major economic, environmental, and reliability implications for California. The CEC's 2008 IEPR recommended that the utilities update their nuclear plants' seismic assessments, and use three-dimensional geophysical seismic reflection mapping and other advanced techniques to supplement ongoing seismic research programs. The CEC subsequently recommended and the California Public Utilities Commission (CPUC) directed the utilities to complete these advanced seismic studies and submit them as part of the CPUC's review of United States Nuclear Regulatory Commission (NRC) license renewal applications for these plants. In August 2010, the CPUC issued Decision 10-08-003, which established, among other things, an Independent Peer Review Panel (IPRP) to conduct a peer review of the proposed seismic study plans and, if the Project is implemented, to review study findings. The IPRP includes staff from the CPUC, CEC, California Seismic Safety Commission, California Coastal Commission (CCC), and County of San Luis Obispo with contract support from the California Geological Survey.

State law. Because there is a significant amount of current data available for the seismic hazard assessment at DCPP, the principal impact of the 3D seismic surveys would be to further refine the source characterization and to, thereby, reduce uncertainty in the model.

23. Given the staffs assessment of the Shoreline fault documented in the RIL that the ground motions from the fault are at or below those for which the plant was evaluated, why is the seismic reevaluation described in the March 12, 2012, request for information necessary?

The RILs scope of review was limited to a deterministic seismic hazard assessment (DSHA) of only one newly discovered fault (i.e., the Shoreline fault) to determine if a safety concern exists at the DCPP based on the new information. By contrast, the seismic reevaluation described in the March 12, 2012, request for information is based on a modern probabilistic seismic hazard assessment (PSHA) model that is developed through a systematic SSHAC Level 3 or Level 4 process and includes all known faults in the area using a process similar to what is done for siting of new reactors.

24. What alternative types of seismic studies (other than 3D high energy) would NRC consider adequate to support a senior seismic hazard analysis committee (SSHAC) level 3 or 4 analysis?

A significant amount of geologic, geophysical and seismic data and information has already been collected, or is planned, as a result of the current site investigation program. The 3D high energy studies are just one part of a much larger program to obtain data and information to characterize seismic hazard. The data sets, taken as a whole, are used to characterize the sources and ground motions at the site. The impact of any one type of data collection is typically a reduction in uncertainty in the final model. The benefit of the 3D high energy seismic surveys to the development of the PSHA model used to respond to the March 12, 2012, request for information issued pursuant to 10 CFR 50.54(f) will be determined by the SSHAC Technical Integration and Peer Review teams in accordance with the SSHAC level 3 process outlined in NUREG 2117, Practical Implementation Guidelines for SSHAC Level 3 and 4 Hazard Studies.

Relative to collection of 3D high energy offshore survey information, the SSHAC Technical Integration and Peer Review teams could consider that the 3D high energy offshore survey information is not warranted because enough information is available from the following sources:

2D and 3D low energy offshore survey information, 3D high-energy on shore survey information, Bathymetric information, Paleoshoreline assessments, Seismic event database reevaluation, Gravity survey data, Magnetic survey data, Regional slip rate analyses,

other sources of new information (e.g., new information available from the U.S. Geological Survey)

If the teams decide that enough information has already been collected such that the 3D high energy seismic surveys are not warranted, the DCPP may still be obligated to perform the 3D high energy offshore survey as part of the commitments made to comply with a California State law.