ML14058A033

Presentation to the Lessons Learned Oversight Board on Oconee Nuclear Station External Flood Protection Concern

ML14058A033
Person / Time
Site:	Oconee
Issue date:	05/05/2009
From:	Jeff Circle NRC/NRR/DRA
To:
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References
FOIA/PA-2012-0325
Download: ML14058A033 (11)

Text

V p Oconee Nuclear Station External Flood Protection Concern May 5,2009 presentation to the Lessons Learned Oversight Board Jeff Circle Division of Risk Assessment Office of Nuclear Reactor Regulation U *!.oS,*R .. dcial Use 0 "ltenfor - Secu t

Background of Issue NRC initiated the Systematic Evaluation Program (SEP) in1977 to review the design of older, operating nuclear power plants with the current Standard Review Plan (SRP).

- Opened Generic Safety Issue GSI-156.1.2, "Dam Integrity and Site Flooding".

- Oconee Nuclear Station (ONS) was identified as one such plant with flooding vulnerability.

- GSI-156 scheduled to be closed out by licensees inthe Generic Letter 88-20, Supplement 4,the Individual Plant Examination of External Events (IPEEE) program.

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Oconee Nuclear Station Three-unit site with unique flooding vulnerability.

- On Lake Keowee near Seneca, SC

- No emergency diesel generators

- Reliance of 2-unit Keowee Dam as sole source emergency ac power

- Site isdownstream of Jocassee Dam

, A385-ft high pumped storage hydro-station holding back Lake Jocassee

- Licensee constructed the Standby Shutdown Facility (SSF) on site to address several issues including flooding

, Houses equipment to safely shut down all 3units inthe event of catastrophic flood to Mode 3

• Licensee constructed 5-ft walls around entrances to address external flooding vulnerability.

, Licensees extended these walls to 7.5-ft inFebruary 2009.

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Flooding

• Licensee performed an ONS inundation study in1992

- Required by Federal Energy Regulatory Commission (FERC) Emergency Action Plan (EAP) on Jocassee license to Duke Hydro

- Only reproducible calculation on record.

, Inundation levels calculated ranged from 12.5 to 16.8 feet

, NRC service water inspection in1994 identified potential deficiency inthe 5-ft entrance wall height to that of the inundation study.

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Licensee Disposition Licensee argued that Jocassee Dam floods are outside of licensing basis for ONS.

Licensee committed to disposition of this deficiency as part of their IPEEE submittal in1995

, An assessment of the Jocassee Dam flood hazard was included inthe IPEEE without mention of the inspection issue.

, The staffs evaluation did not take issue with:

- The derivation of the dam break frequency

- Other factors that the licensee used to reduce their risk estimates of external flood events

- The lack of arguments to justify plant protection for floods in excess of the eight of the protective walls at the SSF grade level.

The licensee failed to note inthe submittal or subsequent updates that there existed a recent inundation study that was the subject of an NRC inspection issue.

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NRC Staff Review of IPEEE Submittals

• Review of submittals for NRR was managed by RES e RES contracted national laboratories to conduct reviews s Region IIstaff met with NRR staff on September 1, 1994 which was documented ina memo

- The Jocassee Dam rupture flood issue was discussed

- NRR staff stated that the external event hazards preliminary review of Oconee would take several months

- The memo stated that NRR staff considered the issue of minimal importance without any bases for these views

- Inlight of this, RES staff was not informed of this issue UjSI RCR 1CB~1T~WO 0 i Ue On6 rmto

NRC Staff Disposition of the Oconee IPEEE Submittal o Given the submittal information, the staffs closeout letter in2000 stated

- Duke's process iscapable of identifying potential vulnerabilities associated with these issues at Oconee

- Considered external event issues resolved.

• The closeout letter cites adominant contributor to residual risk involved Jocassee Dam failures and flood heights exceeding the 5-foot high SSF flood barrier, thus rendering the SSF inoperable.

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Re-emergence of Issue

1. The Reactor Oversight Program (ROP) identified a performance deficiency against the licensee by their making and keeping an opening inthe side of the SSF below the 5-ft level for 2years without an adequate evaluation.

e The flood height calculation resurfaced during evaluation of the performance deficiency using the Significance Determination Process (SDP) in2006 NRC staff reviewed the dam failure probability frequency and discovered a major flaw inthe licensee's calculation in2007.

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Actions Taken by NRC Staff

1. The NRC staff took the following actions to assess the Oconee facility's ability to withstand severe flood events from a postulated Jocassee Dam break:

- Initiated a design adequacy review

- Developed an action plan

- Staff assessed the design basis

- Researched prior licensing actions related to flood protection s Reviewed other information to determine ifthe current plant design meets NRC regulatory expectations

, The staff used a collaborative, consensus-building approach among 4NRR Divisions and OGC to ensure appropriate regulatory practices were followed (e.g., backfit analysis).

, Adraft backfit analysis was prepared (1U.SS RC opte PIucdq Pe~ ard11w Eior 9no

Results of Actions Taken by NRC Staff

, NRC concluded that an adequate protection backfit exception may be the appropriate approach.

, Further determined that additional information from the licensee was required before additional regulatory action isto be taken.

- A10 CFR 50.54(f) request for information letter was sent to licensee on August 15, 2008.

- Licensee responded to the letter on September 26, 2008

- The NRC staff has reviewed licensee's response letter to the 50.54(f) letter and isissuing aformal response.

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Generic Implications s NRC staff has identified six (6)sites which may have a similar flood vulnerability s NRC staff planning on reviewing closeout of GS1-156.1.2 s Aproposed B.5.b review of possible strategies to mitigate core damage s Ageneric communication via an Information Notice has been drafted and isinthe process of concurrence.

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