ML20083K488

Reporting Requirements Carried Out Re Potential over- Stressing of Svc Water Sys Piping & Supports.Evaluation Has Determined Procedure for Verifying Structural Adequacy of Existing Sys.Final Rept Is Forthcomming

ML20083K488
Person / Time
Site:	North Anna
Issue date:	01/26/1979
From:	Brown S VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
References
656B, NUDOCS 7901300059
Download: ML20083K488 (2)

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vinciNia ELECTRIC AND POWER COMP ANY, RiCNhtOND, VIRGINI A 23261 January 26, 1979 P.r. Janes P. O'Reilly, Director Serial No. 656B Office of Inspection & Enforcement PSE&C/GLS:bep/mc U. S. Nuclear Reculatory Comission Region 11 101 P,arietta Street, Suite 3100 Docket No. 50-339 Atlanta, Georgia 30303

Dear Mr. O'Reilly:

L'nder the provisions of 10CFR50.55(e), NRC Region II was notified November 17, 1978, of the potential over-stressing of the Service Water System piping and piping supports during post-LOCA conditions for North Anna Power Station Unit 2.

Pursuant to the requirements of 10CFR21, a 5-day report was submitted on November 22,1978 Serial No. 656.

Further provisions require a 30-day report which was submitted to Region II on December 15, 1973, as an interin report.

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 tercerature nay 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.

Srall bore piping (less than or equal to six inchas in dianeter) and supports are analyzed by more conservative approximate methods and not subject to the concerns of the large bore piping and suoports.

The naturc of the "iging stres analysis.is such thdt"tenrerature differentials are treate:1 absolutely.

Therefore, the analysis for a posi-tive temperature differential of 25F* (yielding a design basis of 95"F) will diso qualify tae piping for a negative ter..perature differential of 25F* (yielding a des.ign basis of 45'F). Pipe supports, however, are not analyzed for temperatures below 70*F.

An evaluation has determined the nost aporopriate procedure for veri-fying the structural adequacy of the existing piping and support system.

This effort.will include a reanalysis of all large bore piping of the Ser-vice Water and Component Cooling Water systems and a review of the large bore pipe supports.

In addition, snall bore piping and supports shall be checxed in sufficient detail to document that the original design is suf-ficiently conservative and that the increased thennal movement of large bore piping can be accornodated. The effect of increased support loads l

on the structure shall also be checked, if required.

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Mr. Jaraes P. O'R: illy 2

The preceding analytical verification will be accomplished for a minimum Service Water (SW) inlet temperature of 30*F, a maximum pre-LOCA SW inlet temperature of 95'F, and a maximun nost-LOCA SU inlet temperature of 115'F. As in the original analysis, a stress-free thermal condition of 70*F will be assuned.

A final report will be submitted when the natum of the solution is deteruined. This report, then, shall be considered an interim report to outline the revised analytical parameters and methodology.

Ver Jt'dly 7

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Seni hicePresident Power tation Engineering e d Construction Mr. John G. Davis, Acting Dire'ctor cc:

Office of Inspection & Enforcement Mr. Harold R. Denton, Director Office of !!uclear Reactor Regulation 6

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REGULAT,0RY I NFOR?!ATI ON DISTEIBUTInfl; SYSTE" ( RIDS)

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.1 ACC 6SION.N 9 :1: N3130035's DOC.DATE: 79/01/26 NO RIZED: No DOCKET *

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?;CI.s. N A "E PECIPIF:1T A. FILI ATIO:'i C) 0'REI LLY, J.P.

Reaion 2, Atlenta, office of the Director SjlJECT: Heoo-tino require-ents have been carried out e ootential C

over-stressino of Svc pt a-Svs nicinc & succorts.

Uv,l e ti'n n 7s c'et e r M na a o"ocor"Jra f or veri f vino strt:c tural C

adeauacy of existina sys.

Final rept forthcoL na.

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TIFLE: CONSTRJCflo'J JiiFICIENCY :?EPORT (10CFR50.55E).

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