ML20012E730
| ML20012E730 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 03/28/1990 |
| From: | Berry K CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9004060187 | |
| Download: ML20012E730 (2) | |
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i Nuclear Regulatory Commission Document Control Desk Washington, DC 20$$5 DOCKET $0-155 - LICLNSE DPR BIG ROCK POINT PLANT -
ADDITIONAL INT 0pJtAT10N RE1ATED TO STATION BLACK 0177 Rift,E 10CFR50.63 Consumers Power Company letter dated April 17. 1989 provided Big Rock Point's response to the Station Blackout Rule 10CPR$0.63. That response was based on the application of NIHARC 87-00. " Guidelines and Technical Basen of NIMARC Initiatives Addressing Station Blackout at Light Water Reactors", and Regulatory Guide 1.15$.
Subsequently in response to NRC Staff concerns regarding licensee implementation of NIHARC 87-00. NtHARC requested that all licenseen provide the NRC with additional information regarding-proper documentation and consistent implementation of NLMARC 87-00 guidance. The purpose of this letter is to respond to the NtHARC recommendation.
Consumers Power Company has reviewed Big Rock Point's response to the Station Blackout Rule and the clarifications to NIMARC 87-00.
Based on this review, we conclude that the information provided in our April 17. 1989 response should be corrected as followc
- 1. The values for Severe Weather (SW) and Extremely Severe Weather (ESW) were incorrectly deternined from Tables 6 and 8 of Reg. Guide 1.155.
These values vere used to assign an Offsite Power Design Characteristic Group for Big Rock Point of P3. Our reevaluation of the estimated frequency of severe and extremely severo weather indicates that Big Rock Point should be classified in the P2 group rather than P3.
This reevaluation indicates that Big Rock Point is at lower risk of a weather-caused station blackout than indicated by our April 17. 1989 letter.
- 2. Our April 17, 1989 letter indicated that Consumers Power Company had selected a target Emergency Diesel Generator (EDG) reliability for Big Rock Point of 0.975. This value was selected based on a calculated average EDG reliability of greater than 0.95 for the last 100 demands. In reviewing these calculations in conjunction with the Plant EDC Reliability Monitoring Program we discovered that we had made an erroneous assumption in 9004069167 900 us A
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determining EDG reliability. Using PRA fatture analysis theory it was incorrectly assumed that one minus the failure probability was equal to J
' reliability of the EDO. Recalculating the reliability of the Big Rock
-Point EDG, using the NSAC-108 methodology, results in the following reliability values for 20. 50, and 100 demands:
20 demands 0.95 50 demands - 0.96 100 demands - 0.97 l
Although our original' calculations of EDG reliability were incorrect. !!ig Rock Point continues to meet the criteria of Reg. Guide 1.155 for EDG reliability based on the recalculated reliabilities.
L in the Big Rock Point response to the Station Blackout Rule. Consumers Power Company committed to meet an EDG target reliability of 0.975. That commitment was based on an incorrect determination of the actual reliability of the Plant u
f' EDC. Based on revised EDG reliability calculations. Consumera Power Company believes the appropriate reliability level for the Big Rock Point EDG is l
l 0.95.
Although the revised EDG reliability calculations result in a commitatnt f
i to a lower overall EDG reliability, the effect on Plant response to a station l
S blackout is minimal. 'As noted in our April 17. 1989 response. Big Rock Point is capabic of maintaining core cooling for a indefinite period without ac t
power.
l Documentation of the applicability of NIMARC 87-00 assumptions, analyses and other related information used in the Big Rock Point response to the Station L
Blackout Rule'is available for review.
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~ Q-Kenneth W Berry
't Director. Nuclear Licensing CC Administrator Region III. USNRC NRC Resident inspector - Palisades j
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