ML13052A782
| ML13052A782 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 02/06/2013 |
| From: | Office of Information Services |
| To: | |
| Shared Package | |
| Property Cell - ML25041A205 | List: |
| References | |
| FOIA/PA-2012-0325 | |
| Download: ML13052A782 (4) | |
Text
Oconee SSF Flood Barrier Breach SDP - Lessons Learned Jeff Circle NRR/DRA/APOB I
-,jjSNRC Purpose
" To brief the RMT of the lessons learned from the disposition of the Oconee Standby Shutdown Facility (SSF) wall SDP finding.
" To discuss potential regulatory actions considered to ensure safety.
2 AJ.S.NRC Discussion Topics
" Background of finding.
" Technical lessons learned.
- Process lessons learned.
" Actions taken to date.
" Considered draft action plan.
Importance of the SSF at Oconee
" The SSF contains the only means to shut all three units down following a station blackout induced by catastrophic flood, fire, or other external events.
" The Oconee site does not have emergency diesel generators.
- On-site emergency ac power is provided by two hydro-electric generators at the Keowee dam.
" Catastrophic flooding to the site can render all the switchyards and Keowee dam unavailable thus blacking out all three units.
- Under these conditions, the additional failure of the SSF function results in core damage.
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- 2U.S.NRC 3
'-ivU!JSNc Aerial View Showing The Relationship of the Oconee Site Environment and Lake Keowee
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I2Ut-NRC 1
Interior and Exterior Walls of SSF The-na Floaceai
-, ir 11N E c The Flood Scenario Rupture of Jocassee Dam 9
jrU.S.NRC Aerial View of Jocassee Dam - Upstream of the Oconee Site eo~ur~co c--
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<IA14.rC L-II li SSF Catastrophic Flood Heights Given Rupture of Jocassee Dam Licensee study in 1980s established a resultant flood height of approximately 5 feet.
- Justification for erection of the 5-ft wall around the doorway.
- Study is unavailable.
- Flood height almost matches that of overtopping of Keowee dam.
Licensee commissioned additional study by FERC in 1992.
- Established a higher resultant flood height range of 12-16 feet.
- Licensee still used the 5-ft height for their IPEEE submittal developing a 20% split fraction apportioning the Jocassee Dam rupture frequencies to account for these higher FERC flood heights.
1J.
NRC Background Summary
- August 17, 2006 - SERP meeting assessed as preiminary WHITE based on a blended qualitative and quantitative risk-informed approalh (pre-IMC 0609 App M).
August 31, 2006-Choice letter sent to licensee.
October 5, 2006 - Licensee provided written response to choice letter and waived regulatory conference.
Nov. 22, 206 - Final significance determination issued WHITE based on qualitative erosion of defense-in-epth, but includes quantitative CDF based on apportioning flood frequency to flood height.
December 20, 2006 - Licensee appeals the final significance determination.
Requests NRC to accept incomplete, un-docketed new information on Jocassee dam seismic failure.
- Appeal panel convened on January 9, 2007.
Licensee contractor seismic fragility analysis of Jocassee issued January 29, 2007.
March 1,2007 - Appeal panel upheld the WHITE finding.
May 3, 2007 - Licensee requests reassessment of Final significance determination
- June, 2007 - Assembled a team to review new information. Flooding expert review of data on random dam failure.
June 28.2007 - Follow up telecom with Licensee on dam failure questions and comments.
July 17. 2007 - Licensee response to analysis questions by email.
September 5, 2007 - Final SERP split vote forces upper management resolution.
November 20, 2007 - Final determination letter released to licensee.
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-Mfia 12 U.<US.
.N.RIC 2
Jocassee Dam Random Failure Frequency Licensee developed random dam failure frequency for IPEEE submittal based on rockfill dam failures per population of earthen, rockfill, and composite dams.
- Severely underestimated frequency by an order of magnitude at 1.4E-5 per year.
As part of the second appeal, James Vail of NRR/
DRA/APOB investigated the derivation of this frequency.
- Found that 2 failures in 14,425 dam-years was more appropriate for Jocassee which yielded a frequency of 1.8 x 104 per year 90% credible interval of [6.5 x1 0-/yr, 3.4 x1 0"4yr]
131-IU.S.NRC Industry Evaluations
- Only two IPEEEs addressed dam failure floods quantitatively-Ft Calhoun and Diablo Canyon.
- Others only addressed probable maximum precipitation and screened out dam failure as low probability.
- Due to lack of sources NUREG/CR-5042, "Evaluation of External Hazards to Nuclear Power Plants in the United States", was used which derived NSAC/60 (the Oconee PRA) as its source.
- The estimate of 2.5E-05/dam-year in NSAC/60 was done in error by an order of magnitude and it propagated throughout the industry.
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..ý2U.S.NRC SPAR Considerations for External Flood Dams as far up or downstream as 300 miles should be considered for both flood and loss of heat sink, It is noteworthy that all forms of dams have a failure rate between 1E-4 and 4E-4, even for random 'sunny day" events.
Oetermining flood levels, however, is a complex matter. The USACOE has software named HEC RAS that when combined with GIS geographical data will model river flow and flooding in great detail.
Weather based floods remain in the deterministic world because the input conditions are always from the same source as was used in the original plant design basis. Besides, the growth of the maximum precipitation only increases about 20% when a 100 year interval is compared to a 1000 year interval. With only 100 years of data available In many locations, projecting beyond a 1 E-3/yr event is very uncertain anyway.
__ ________wa 15 C 2U. R Process Lessons Learned
- Process did not account for situations where licensee did not communicate to the regional office and waived participation in a regulatory conference.
- Process did not accept new information prior to final determination.
- Without a regulatory conference, communication was impacted to program office and regional management of potential greater-than-green SDP findings.
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,IkUS.NRC Actions Taken I IMC0609 in draft revision to account for:
- Licensees may present new information provided that they informed the agency either during a regulatory conference or in writing before the final significance determination is made.
New information has to be submitted within the 30-day appeal period.
- Using best available information to determine final significance in a timely manner.
NRR concurrence with regional management on accepting an appeal.
17 7,1US.NRC Actions Taken (cont'd) a Training conducted to regional Senior Reactor Analysts (SRAs) in October 2007 counterparts meeting.
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Draft Action Plan to Consider Future Actions
" NRR Program Office Director and/or Deputy Director should be informed of all greater-than-green findings.
" Exploration of licensing and potential backfit requirement for protection against most likely flood.
" Generic communication to licensees on flooding.
19,;tU.S.NRC Draft Action Plan to Consider Future Actions (Cont'd)
" Update of RASP manual for additional external flood guidance.
" Consider an update to NUREG/CR-6928 to include rupture frequencies.
" NRO Licensing and Design Bases Review for New Reactor Licensing to incorporate lessons learned on new applications.
" Develop a Temporary Instruction to assess licensee performance in this area.
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