ML13056A099
| ML13056A099 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 02/06/2013 |
| From: | NRC/NRR/DRA |
| To: | |
| References | |
| FOIA/PA-2012-0325 | |
| Download: ML13056A099 (13) | |
Text
Oconee SSF Flood Barrier Breach SDP-Lessons Learned Mike Franovich, DRA.
Jeff Circle, DRA/APOB.
James Vail, DRA/APOB.
Paul Bonnett, DIRS/IRIB.
E RUNIED STATES NUCLEAR REGULATORY COMMISSION IU Protecting People and the Environment
Objectives
- Purpose
- To inform the ET and LT of the lessons learned from the disposition of the Oconee Standby Shutdown Facility (SSF) wall SDP finding.
- Measure for Success ET and LT members understand safety and security issues of this finding.
ET and LT members understanding of the continuous improvement of the SDP appeal process.
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Discussion Topics
- Background of finding.
" Technical lessons learned.
- Process lessons learned.
- Actions taken.
" Considered future actions.
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The Flood Scenario Rupture of J Fý i koý OcneSt ocassee Dam Protecting People and the Environment
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F The Flood Barrier Finding Licensee opened an access cover uncovering a previously cut hole in the wall on August 13, 2003.
Should have done a 10CFR50.65 (a)(4) assessment immediately.
Should have done a 10CFR50.59
'T evaluation after 90 days.
Licensee opportunities to identify issue June 2, 2005 NRC inspectors notified the licensee of condition.
Licensee issued PIP (condition report in their corrective action system). Corrective action not taken.
August 3, 2005 NRC inspectors Five-foot flood wall questioned lack of corrective action protecting the doorway.
and licensee issued a further PIP.
Opening sealed on August 3, 2005.
n outside wall with access pl~ate on inside of SSF building.
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Background===
- August 17, 2006 - SERP meeting assessed as preliminary WHITE based on a blended qualitative and quantitative risk-informed approach (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, 2006 - Final significance determination issued. WHITE based on qualitative erosion of defense-in-depth, 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.
March 1, 2007 - Appeal panel upholds 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.
October, 2007 - Final Determination Letter pending.
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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, 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 10.
Oper year 90% credible interval of [6.5 xl 0-5/yr, 3.4 xl 0 -4/yr]
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Technical Lessons Learned Investigation of Dam Failure Frequencies http://crunch.tec.army.miI/nid/webpages/nid.cfm
.http://npdp.stanford.edulindex.htmI All Arch Dams All Buttress Dams All Concrete Dams All Earth Dams All Gravity Dams All Masonry Dams All Multi-Arch Dams All Rockfill Dams All Stone Dams All Timber Crib Dams Total Buttress Dams Over 50 Feet Arch Dams Over 50 Feet Concrete Dams Over 50 Feet Earth Dams Over 50 Feet Gravity Dams Over 50 Feet Masonry Dams Over 50 Feet Multi-Arch Dams Over 50 Feet Rockfill Dams Over 50 feet Total Failures 2
2 10 366 28 5
0 7
2 3
425 Failures 0
2 0
56 7
0 0
4 69 Dam-years 9101 9819 110227 2240403 122798 21692 240 55872 11365 6536 2605987 Dam-years 1876 5667 19215 144810 19542 1987 77 19900 213184 Mean 2.1 E-04 1.9E-04 9.3E-05 1.6E-04 2.3E-04 2.2E-04 1.5E-04 1.3E-04 1.7E-04 3.6E-04 1.6E-04 Mean 2.OE-04 2.8E-04 8.2E-05 3.8E-04 3.2E-04 2.OE-04 2.4E-04 2.1 E-04 2.4E-04
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Licensee Evaluations
- Only two IPEEEs addressed dam failure floods quantitatively - Ft Calhoun and Diablo Canyon. Everyone else only addressed probable maximum precipitation and screened out dam failure as low probability.
- Unfortunately, there were few dam failure data sources around back then, so many plants used the estimate published in NUREG/CR-5042. The data source for the estimate in NUREG/CR-5042 was the Oconee PRA - NSAC/60. 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.
References:
NUREG/CR-5042, "Evaluation of External Hazards to Nuclear Power Plants in the United States.
NSAC/60, "Oconee PRA" wUw w
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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 impacte to program office and regional management of potential greater-than-green SDP findings.
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Actions Taken
- 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.
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Actions Taken (cont'd)
- Training conducted to regional Senior Reactor Analysts (SRAs) in recent counterparts meeting.
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Considered 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.
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