ML13052A782

Slides on Oconee Ssf Flood Barrier Breach SDP - Lessons Learned

ML13052A782
Person / Time
Site:	Oconee
Issue date:	02/06/2013
From:	Office of Information Services
To:
References
FOIA/PA-2012-0325
Download: ML13052A782 (4)

Text

Purpose Oconee SSF Flood Barrier " To brief the RMT of the lessons learned Breach SDP - Lessons from the disposition of the Oconee Learned Standby Shutdown Facility (SSF) wall SDP finding.

" To discuss potential regulatory actions considered to ensure safety.

Jeff Circle NRR/DRA/APOB I -,jjSNRC .............. . 2 AJ.S.NRC Importance of the SSF at Oconee Discussion Topics

" The SSF contains the only means to shut all

" Background of finding. three units down following a station blackout induced by catastrophic flood, fire, or other

" Technical lessons learned. external events.

" The Oconee site does not have emergency

• Process lessons learned. diesel generators.

" Actions taken to date. - On-site emergency ac power is provided by two hydro-electric generators at the Keowee dam.

" Considered draft action plan. " 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 incore damage.

3 '-ivU!JSNc -M-A--... 4 ;2U.S.NRC Aerial View Showing The Relationship of the Oconee Site Environment and Lake Keowee

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Interior and Exterior Walls of SSF The-na Floaceai -,ir 11N Ec The Flood Scenario Aerial View of Jocassee Dam - Upstream of the Rupture of Jocassee Dam Oconee Site 9 jrU.S.NRC eo~ur~co c-- 10

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SSF Catastrophic Flood Heights Given Background Summary Rupture of Jocassee Dam

• 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.

Licensee study in 1980s established a resultant flood

• October 5, 2006 - Licensee provided written response to choice letter and waived regulatory conference.

height of approximately 5 feet.

• Nov.22, 206 - Final significance determination issued WHITE based on qualitative erosion of defense-in-epth, but includes quantitative CDF based on apportioning

- Justification for erection of the 5-ft wall around the doorway. flood frequency to flood height.

- Study is unavailable.

• December 20, 2006 - Licensee appeals the final significance determination.

Requests NRC to accept incomplete, un-docketed new information on Jocassee failure.

- Flood height almost matches that of overtopping of Keowee dam seismic dam.

• Appeal panel convened on January 9, 2007.

• Licensee contractor seismic fragility analysis of Jocassee issued January 29, 2007.

Licensee commissioned additional study by FERC in March 1,2007 - Appeal panel upheld the WHITE finding.

1992.

• May3, 2007 - Licensee requests reassessment of Finalsignificance determination

• June, 2007 - Assembled a team to review new information. Flooding expert review

- Established a higher resultant flood height range of 12-16 feet. of data on random dam failure.

- Licensee still used the 5-ft height for their IPEEE submittal June 28.2007 - Follow up telecom with Licensee on dam failure questions and developing a 20% split fraction apportioning the Jocassee Dam comments.

• July 17. 2007 - Licensee response to analysis questions by email.

rupture frequencies to account for these higher FERC flood

• September 5, 2007 - Final SERP split vote forces upper management resolution.

heights.

• November 20, 2007 - Final determination letter released to licensee.

" 1J. - NRC r -Mfia 12 U.<US. .N.RIC 2

Jocassee Dam Random Failure Industry Evaluations Frequency

• Only two IPEEEs addressed dam failure floods Licensee developed random dam failure frequency for quantitatively- Ft Calhoun and Diablo Canyon.

IPEEE submittal based on rockfill dam failures per

• Others only addressed probable maximum precipitation population of earthen, rockfill, and composite dams. and screened out dam failure as low probability.

- Severely underestimated frequency by an order of magnitude at 1.4E-5 per year.

• Due to lack of sources NUREG/CR-5042, "Evaluation of As part of the second appeal, James Vail of NRR/ External Hazards to Nuclear Power Plants in the United DRA/APOB investigated the derivation of this frequency. States", was used which derived NSAC/60 (the Oconee

- Found that 2 failures in 14,425 dam-years was more appropriate PRA) as its source.

for Jocassee which yielded a frequency of 1.8 x 104 per year 90% credible interval of [6.5 x1 0-/yr, 3.4 x10"4yr] - 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.

131-IU.S.NRC 14 . . .ý2U.S.NRC SPAR Considerations for External Flood Process Lessons Learned Dams as far up or downstream as 300 miles should be considered for both

• Process did not account for situations where 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. licensee did not communicate to the regional office and waived participation in a regulatory Oetermining flood levels, however, is a complex matter. The USACOE has software named HEC RAS that when combined with GIS geographical data conference.

will model river flow and flooding in great detail.

• Process did not accept new information prior to Weather based floods remain in the deterministic world because the input final determination.

conditions are always from the same source as was used in the original plant design basis. Besides, the growth of the maximum precipitation only

• Without a regulatory conference, increases about 20% when a 100 year interval is compared to a 1000 year communication was impacted to program office interval. With only 100 years of data available Inmany locations, projecting beyond a 1E-3/yr event is very uncertain anyway. and regional management of potential greater-than-green SDP findings.

__ ________wa 15 C 2U . R -1 ,IkUS.NRC Actions Taken Actions Taken (cont'd)

IIMC0609 in draft revision to account for:

a Training conducted to regional Senior

- Licensees may present new information provided that they informed the agency either during a regulatory Reactor Analysts (SRAs) in October 2007 conference or in writing before the final significance counterparts meeting.

determination is made.

- New information has to be submitted within the 30-

• Met with NSIR to inform DHS on potential day appeal period. dam and other outside infrastructure

- Using best available information to determine final significance in a timely manner. vulnerability.

- NRR concurrence with regional management on accepting an appeal.

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Draft Action Plan to Consider Draft Action Plan to Consider Future Actions Future Actions (Cont'd)

" NRR Program Office Director and/or " Update of RASP manual for additional Deputy Director should be informed of all external flood guidance.

greater-than-green findings. " Consider an update to NUREG/CR-6928

" Exploration of licensing and potential to include rupture frequencies.

backfit requirement for protection against " NRO Licensing and Design Bases Review most likely flood. for New Reactor Licensing to incorporate lessons learned on new applications.

" Generic communication to licensees on

" Develop a Temporary Instruction to flooding.

assess licensee performance in this area.

19 ,;tU.S.NRC 20 <ý2US.NRC 4