ML14058A032

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

ML14058A032
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: ML14058A032 (8)

Text

Oconee Nuclear Station External Flood Protection Issue Presentation to the Lessons Learned Oversight Board May 5,2009 Jeff Circle Division of Risk Assessment Office of Nuclear Reactor Regulation Off icia S nly - Securi 1U.S.NRC elated I ormatio Prwi.u*

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Background of Issue Oconee Nuclear Station Three-unit site with potentially unique flooding vulnerability:

- On Lake Keowee near Seneca, SC.

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

- Site is11 miles downstream 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 internal flooding:

• Houses equipment to safely shut down all 3units (to Mode 3) inthe event of catastrophic flood.

1. Licensee constructed 5-ft walls around entrances to address external flooding vulnerability from aJocassee Dam rupture.

oLicensee extended these walls to 7.5-ft inFebruary 2009.

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Site Inundation Study

, Licensee performed a Jocassee Dam rupture inundation study in1992.

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

Calculated inundation levels at ONS ranged from 12.5 to 16.8 feet above SSF grade and clearly above flood protection walls.

NRC Service Water System Operational Performance Inspection (SWSOPI) in1994 identified potential deficiency inthat the 5-ft entrance wall height was significantly less than that predicted by the inundation study.

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Licensee Disposition

1. Licensee stated that Jocassee Dam rupture floods are outside of licensing basis for ONS.

s Licensee committed to addressing this apparent lack of flood protection inits IPEEE submittal in1995.

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

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NRC Disposition s Review of IPEEE submittals to NRR was managed byRES.

@Region IIservice water inspection staff met with NRR staff on September 1,1994 to discuss several issues arising from the inspection:

- NRR staff considered the SSF flood protection issue of minimal importance and did not provide any bases for these views.

- RES staff was not informed of the lack of resolution of the Jocassee Dam rupture SSF flood inundation issue.

@NRC staff issued standard close-out letter to the licensee which resolved most IPEEE issues identified inNUREG-1407.

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Rememergence of Issue

• The Reactor Oversight Process (ROP) evaluated a licensee performance deficiency arising from an opening made inthe side of the SSF below the 5-ft flood protection level for 2years without an adequate evaluation.

Concerns over adequacy of the SSF wall and the 1992 flood height calculation results resuraced during evaluation of the performance deficiency using the Significance Determination Process (SDP) in 2006.

, NRC staff reviewed the dam failure probability frequency and discovered aflaw inthe licensee's calculation in2007.

Final determination of finding was found to be of WHITE significance.

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Actions Taken by NRC Staff NRR concluded that the protection of the Oconee site from external flooding was an adequate protection issue with the following actions taken:

- Issued a 10 CFR 50.54(f) letter requesting information on consequences and how the licensee addresses adequate protection of the site against external floods.

- Determined basis for allowing short-term continued operation of the facility.

- Now interacting with the licensee.

Evaluation of potential generic flooding issues at other sites.

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Conclusions Several opportunities were missed:

In1994, NRC reported that the licensee removed external flood protection of the SSF from the Oconee UFSAR and downgraded itto a "PRA issue".

- NRC accepted this and did not question the licensee's rationale used for removal of Jocassee Dam rupture and SSF flood protection.

- NRC did not address the licensing basis impact beyond that of PRA.

e The SWSOPI team members met with NRR inSeptember 1994:

- No written basis was given for the decision by NRR not to consider the importance of high dam rupture frequency and consequence when passing the IPEEE submittal to RES for review.

- No tracking of this issue was made when the review was returned to NRR for issue of the closeout letter.

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