ML20064H441
| ML20064H441 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 12/15/1978 |
| From: | Brown S VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| References | |
| NUDOCS 7812200225 | |
| Download: ML20064H441 (2) | |
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December 15, 1978 ifr. James P. O'Reilly, Director Serial llo. 656A Office of Inspection & Enforcement PSE&C/GLS/beo:me U. S. Nuclear Regulatory Comission Region II
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101 tiarietta Street, Suite 3100 Docket No. 50-339 Atlanta, Georgia 30303
Dear Mr. O'Reilly:
Under the provisions of 10CFR50.55(e), NRC Region II was notified November 17, 1978, of the potential over-stressing of the Service Water System pioing and piping supports during post-LOCA conditions for North Anna Power Station Unit 2.
The original design basis of the Service Water System is for a maxi-mum service water reservoir temperature of 95'F.
Present analyses indi-cate that the reservoir temperature may exceed 95'F after a postulated LOCA. The stress analysis for the large bore piping is for a maximum Service Water temperature of 95'F.
Loads on pipe supports are generated by the piping stress analysis, and therefore, the supports are potentially over-stressed during the post-LOCA condition. Small bore piping (less than or equal to six inches in diameter) and supports are analyzed by more conservative approximate methods and not subject to the concerns of the large bore piping and supports.
The nature of the piping stress analysis is such that temperature dif-ferentials are treated absolutely. Therefore, the analysis for a positive temperature differential of 25F* (yielding a design basis 95'F) will also cualify the piping for a negative temperature differential of 25F* (yielding a design basis of 45'F). Pipe supoorts, however, are not analyzed for tem-peratures below 70*F.
An evaluation to determine the most appreoriate procedure for verify-ing the adecuacy of the existing piping system is being conducted. The re-salts of a re-analysis will determine if remedial modifications to the exist-ing system are recuired. Ultimately, the system will be designed to accom-mocate all postulated loading conditions.
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i' Mr. James P. O'Reilly 2
Tnis 30-day report shall be considered an interim report to outline the general approach that will be followed to investigate this potential deficiency. A final report will be submitted by February 1,1979, to de:ument the measures to be taken to insure the design capability of the Service Water System.
Very.truly yours, Sam 5. Brown,Jr.
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Vice President - Power Station Engineering and Construction cc: Mr. John G.- Davis, Acting Director Office of Inspection & Enforcement N.HaroldR.Denton, Director Office of Nuclear Reactor Regulation