ML14058A050

Questions and Answers Related to Oconee Flood Barrier

ML14058A050
Person / Time
Site:	Oconee
Issue date:	02/04/2014
From:	Office of Information Services
To:
Shared Package
ML14055A421	List: ML090570117 ML090680737 ML091620669 ML092020480 ML092940769 ML100280954 ML101750619 ML101890803 ML102990064 ML103410042 ML12268A404 ML14055A410 ML14055A411 ML14055A474 ML14058A015 ML14058A016 ML14058A017 ML14058A018 ML14058A019 ML14058A020 ML14058A021 ML14058A022 ML14058A023 ML14058A024 ML14058A025 ML14058A026 ML14058A027 ML14058A028 ML14058A029 ML14058A030 ML14058A031 ML14058A032 ML14058A033 ML14058A034 ML14058A035 ML14058A036 ML14058A037 ML14058A038 ML14058A039 ML14058A040 ML14058A042 ML14058A043 ML14058A044 ML14058A045 ML14058A046 ML14058A047 ML14058A048 ML14058A049 ML14058A050 ML14058A051 ... further results
References
FOIA/PA-2012-0325
Download: ML14058A050 (1)

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Questions and Answers Related to Oconee Flood Barrier

1. How much confidence does NRR has about the fact the licensee's estimate of the Flood Freauency in its IPEEE is one order of lower based on operating experience?

We have very high confidence in our calculation. Attached is a spreadsheet comparing our experience data with the Oconee PRA and IPEEE calculations. Their error is the counting of only 2 failures of rockfill dams and then applying them to the population of both rockfill and earthen dams. During the same period (1940 to 2000) earthen dams had 32 failures. Had these 32 failures been properly included, the failure frequency would have been 2E-4 failure per dam year. If rockfill dams had been used alone, they would have gotten about the same result. There is no dam or mixture of dam populations that would get a result less than 1E-4 failure per dam year. Their result of 1.3E-5 is clearly in error.

References:

• National Inventory of Dams http://crunch.tec.army.milinid/webpagesinid.cfm

• National Performance of Dams Program http://npdp.stanford.edu/index.html

• Oconee IPEEE Rev 2 Section B.4.3, "Frequency of Dam failure"

2. Are there other IPEEEs which postulate external floods induced by dam failures? If there are, what are the frequencies, which those licensees used to assess risk?

NUREG-1742 identified only two IPEEEs that 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 calculation in NSAC/60 was done in error and it propagated throughout the industry.

References:

• NUREG/CR-5042, "Evaluation of External Hazards to Nuclear Power Plants in the United States.

• NUREG-1742, "Perspectives Gained From the Individual Plant Examination of External Events (IPEEE) Program

• NSAC/60, "Oconee PRA"

3. How much confidence do we have on licensee's Predicted flood height (1980s study) that estimate the flood height at 4.71'? level?

The licensee indicated that their calculations to support the 1983 study were not retrievable and personnel who performed the work wire not available. The staff has attempted to reconstruct what may be the logic for the original 4.71 foot flood level estimate as follows:

The benchmark nearest to the SSF shown on the Oconee site plan from the FSAR is at 796.63' elevation, Lake Keowee is maintained at 800' elevation. The difference is 3.37'. In the absence of any documented analysis, the basis for 4.71' is a mystery. Both the Oconee PRA and the IPEEE are silent on the 4.71' height and only mention the 5' height and even that is without explanation. However the plant does claim a probable maximum precipitation of 1.33' which when added to 3.37' would come out to 4.70' but that is speculation. Oconee never claimed it.

The plant is protected from lake Keovwee by a 20' or so dike that surrounds the intake area and a similar dike that forms an extension of the Keowee dam. The east side of the site slopes down into the river valley. If the waters of lake Keowee find a path into the west yard, the east side slope may not drain them away fast enough to maintain less than 5 feet of water in the west yard. If the Keowee dam faif, the..

valley to the east w guickl V =d oua*bWt 3.37 feet of water into the west yarox

• q vi-e 192 FERC rToob model of 4_-. assee dam failure put 12.5 to 16B -rfeel e*W o611owina failure of the Keowee

^,-site dam [-i now unavailable T"*Duke stuuy iidicaied the Keowee dam wvbuio survive-ana a o Tot "arrier in the yard was adequate. Duke has not presented the 1992 FERC flood model as a design basis.