ML090700525
| ML090700525 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 11/21/2008 |
| From: | Pacific Gas & Electric Co |
| To: | Office of Nuclear Reactor Regulation |
| Wang, A B, NRR/DORL/LPLIV, 415-1445 | |
| Shared Package | |
| ML090700508 | List: |
| References | |
| TAC ME0174, TAC ME0175 | |
| Download: ML090700525 (2) | |
Text
New Potential Seismic Fault NRC Briefing November 21, 2008 PG&E ATTENDEES Name Title e-mail Phone Jim Becker Site VP JRB1 x-3462 Ken Peters Station Director KJPa x-4888 Jim Welsch Director, Operations JMW1 x-3242 Bill Guldemond Director, Site Services WGG4 x-4369 Lloyd Cluff Director, Geosciences LSC2 415-973-2791 Pete Resler Director, Communications PCR4 x-3771 Norm Abrahamson Seismic Engineer NAA2 415-973-2989 Rich Klimczak Manager, Design Engineering RLK1 x-6513 Stan Ketelsen Manager, Regulatory Services SCK3 x-4720 Terry Grebel Manager, Regulatory Projects TLG1 x-4160 Jearl Strickland Manager, ISFSI LJS2 x-6080 Larry Parker Supervisor, Regulatory Services LMP1 x-3386 NRC ATTENDEES Name Title Vincent Gaddy Branch Chief, Region IV Michael Peck Senior Resident Inspector Tony Brown Resident Inspector Alan Wang Project Manager, NRR Yong Li NRO/DSER/RGS2 Michael Markley NRR LPL4 Branch Chief Annie Kammerer RES/DE/SGSEB George Thomas NRO/DSRA/SRSB Kamal Manoly NRR Mechanical & Civil Engineering Branch Chief
Reference:
Notification 50086062, and PowerPoint Slides I Introductions II Summary of new Seismicity data: Lloyd Cluff described the USGS' ongoing five-year study of the Central Coastal California Region, which just completed the second year. The study uses new technology including aero-magnetic and marine-magnetic data coupled with more detailed re-analysis of micro quake
(<3.5M) data to more accurately locate epicenters of small earthquakes.
Preliminary results were reviewed with PG&E's geosciences department earlier this month. The preliminary results show a lineament of approximately 25 earthquakes paralleling the coastline approximately 1 km offshore. The epicenters range from 4-14 km deep and are believed to be vertical strike-slip.
Norm Abrahamson described the potential range in length of the postulated fault and correlated this to an expected maximum magnitude of 6.25 to 6.5M. The resultant ground motion at the plant would be below the design basis Hosgri at the critical frequency for the power block.
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New Potential Seismic Fault NRC Briefing November 21, 2008 It was emphasized that the data is very preliminary and that it would be more definitive by April. In addition, the USGS is planning on gathering additional offshore data next summer, which will be incorporated in the final report forecast for summer 2010.
Questions:
If the largest measured earthquake in this zone was 3.5M, why is PG&E concluding the potential fault has the capability of generating a 6.5M earthquake?
The magnitude is based on a fault length, which is conservatively assumed to be 24 km.
What is the uncertainty in the location of these epicenters given they are offshore and our sensors are onshore? The sensors are located on point Buchon at the northern and Lighthouse Point on the southern end of the zone. These sensors have been calibrated to confirm an accuracy of approximately 1 km.
Is surface faulting possible? Surface faulting is possible above 6M. Maximum displacement offshore is postulated to be up to 0.5M. This new fault could result in on-shore soil deformation of a few cm.
Is a stronger tsunami possible? Given that this new fault appears to be a "strike-slip" fault without significant vertical component, it would not generate a tsunami.
Sub-surface nearby landslide potential has also been evaluated and concluded to not be an increased threat.
When will PG&E have additional information and a written plan? PG&E expects to send NRC an action plan the week of December 8, 2008.
What communication has taken place or is planned? PG&E has briefed local officials earlier this week and plan to brief the local media later today. PG&E will issue a 50.72 notification prior to the press briefing. PG&E has also been communicating with State seismic and energy commissions.
III Operations: Jim Welsch summarized the operability determination that was performed on November 14. Based on the preliminary nature of the information and the understanding that ground motion from this postulated fault would still be enveloped by the Hosgri, SSCs remain operable.
IV Engineering: Rich Klimczak summarized the ongoing engineering evaluations that will be performed as details become available.
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