ML20127N374

Supplemental SE Accepting Analysis & Results in Response to SBO rule,10CFR50.63

ML20127N374
Person / Time
Site:	Cooper
Issue date:	11/19/1992
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20127N362	List: ML20127N358 ML20127N374
References
NUDOCS 9212010212
Download: ML20127N374 (3)

Text

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t ENCLOSURE SUPPLEMENTAL SAFETY EVALVATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION STATION BLACK 0UT RULE (10 CFR 50.63)

EllMSKA PUBLIC POWER DISTRICT COOPER NUCLEAR STATION QOCKET NO. 50-298 1.0 JNTRODUCTION The NRC staff's Safety evaluation (SE) and Supplemental Safety Evaluation (SSE) pertaining to the Nebraska Public Power District's (the licensee's) responses to the Station Blackout (SBO) Rule,10 CFR 50.63, was transmitted to the licensee by letters dated August 22, 1991, and June 30, 1992, respectively. The staff's SSE found the licensee's proposed method of coping-with an SB0 to be acceptable except that pertaining to the weather analysis of extreme wind speeds. As a L result, the staff determined that the plant required an emergency diesel generator (EDG) target reliability of 0.975 in order for the plant to remain a j 4-hour SB0 coping plant, whereas the licensee determined an EDG target reliability of 0.95.

! The licensee responded to the staff's SSE by letters dated August 11, and l September 15, 1992. The following is-an evaluation of-these responses.

l 2.0 EVALVATION l

The licensee's August II,1992, extreme wind calculations were based on a set of

! monthly fastest-minute wind speeds taken at the Cooper Nuclear Station. Data l points for 36 months from 1989 through 1991 were used in the calculations. The resultant expectan:y uf extreme winds exceeding 125 mph were calculated to be 1.98E-6 per year. The staff was unable to accept this result because it was based on only 3 years of data and because the result was 2 to 3 orders of magnitude less than for the surrounding. areas, and as listed in NUMARC 87-00, Table 3.2.

The licensee's September 5,1992, submittal provided the calculated results based on the Omaha fastest-mile wind speeds for the 1936 to 1977 period, as obtained from-the NBS Building Science Series 118, U. S. Dept. of Commerce, issued March 1979. This calculation resulted in an expectancy of extreme winds t

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. exceeding 125 mph of 9.5E-4 per year. This results in an extreme severe weather (ESW) classification of "2" for the site. A similar calculation for wind speeds greater than 75 mph resulted in an expectancy of 12.9E-2 per year. This results l in a severe weather (SW) classification of "2" for the site. The ESW2 and SW2 1 classifications, when combined with the other site characteristics, result in a "Pl" offsite ac power design characteristic, a 4-hour SB0 coping requirement, l

and an 0.95 EDG target reliability.

The staff finds the licensee's revised determination nf ESW2 and SW2 to be acceptable. The staff previously found a similar calculation to be acceptable for Fort Calhoun which is in the same general area. In reaching its determination, the staff also noted that other surrounding sites (Wolf Creek,

Callaway, and Duane Arnold) are "Pl" sites, a

3.0

SUMMARY

AND CONCLUSION The licensee has presented an additional extreme wind analysis to support its determination that the Cooper station qualifies as a "Pl" (offsite ac power design characteristic) site, with a 4-hour SB0 coping requirement and 0.95 EDG target reliability. The staff finds this revised analysis and the results to be acceptable.

The documentation of the latest analysis should be included with the other documentation to be maintained by the licensee in support of the SB0 Rule a implementation for possible future NRC audit.

Principal Contributor: A. Toalston Date: November 19, 1992

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