ML19256C758
| ML19256C758 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 03/29/1979 |
| From: | Bryan S, Nolan F NRC OFFICE OF INSPECTION & ENFORCEMENT (IE) |
| To: | |
| References | |
| PNO-79-068, PNO-79-68, NUDOCS 7910120433 | |
| Download: ML19256C758 (2) | |
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PRELIMINARY NOTIFICATION March 29, 1979 PRELIMINARY NOTIFICATION OF EVENT OR UNUSUAL OCCURRENCE--PNO-79-68 This preliminary notification constitutes EARLY notice of event of POSSIBLE safety or public interest significance.
The information presented is as initially received without verification or evaluation and is basically all that is known by IE staff on this date.
FACILITY:
Virginia Electric and Power Company North Anna Unit No. 1 Docket No. 50-338 Mineral, Virginia
SUBJECT:
POTENTIAL OVERSTRESS OF SAFETY RELATED PIPING CAUSED BY ACTUAL WEIGHT OF 6-INCH VELAN VALVES (ACTUAL WEIGHT DOUBLE DESIGN WEIGHT)
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This supplements PN0 79-64 dated March 27, 1979.
Since the previous notice, Stone and Webster (S&W) has reanalyzed seismic stresses for low head safety injection piping to the reactor coolant loop hot leg by using the correct weight for the installed 6-inch Velan check valves.
These new analyses produced results indicating that during a design basis earthquake, stre. s applied to the piping between two check valves would be 11% above the code specified yield strength of 30,000 psi.
- However, the licensee has stated that the as built material certification on file for this section of the low head safety injection piping shows that the yield strength is actually 34,900 psi; whereas the maximum calculated stress to this section of piping during a seismic event would be 34,215 psi.
Calcula-tions also indicated two other areas of the pipe which are stressed approximately 7% above the code specified yield strength for these piping materials of 25,020 psi.
These areas are (1) elbow located between the inboard check valve and the reactor coolant system and (2) the entrance of the 6-inch pipe in the reactor coolant system.
The licensee has stated that the as-built material certification for the elbow is actually 31,320 psi; vhereas the maximum calculated stress for the elbow is 26,720 psi.
The aa-built material certification for the 6-inch pipe at the entrance of the reactor coolant system is actually 31,820 psi, whereas the maximum calculated s.ress for this section is 26,761 psi.
The licensee plans to shutdown and complete appropriate modifications prior to April 16, 1979 to assure that the piping stresses are within code allowable stresses.
NRR and IE have reviewed this matter and concur that this problem is difierent from the overstress problem at Surry which resulted in plant shi tdown; that isj this pipe would not be expected to fail in the event of a design basis earthquake because the as-built would not be overstressed.
An
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IE Bulletin is scheduled to be issued to all licensees concernina
' reanalysis of piping which used incorrect weights for Velan valves.
CONTINUED 1452 328
/g910120
Continued March 29,.1979 Page 2 PNO-79-66 Region II (Atlanta) received additional information concerning this occurrence by telephone from the resident inspector and VEPC0 on March 28 and 29. This information is current as of 11:00 a.m. on March 29.
Contact:
FNolan, IE x28019 SEBryan, IE x28019 Distribution:
Transmitted H St _b h'N Chairman Hendrie Commissioner Bradford S. J. Chilk, SECY Comissioner Kennedy Commissioner Ahearne C. C. Kammerer, CA Comissioner Gilinsky (ForDistribution)
- h P. Bldg h ' h f J.G. Davis,y/[d Transmitted: MNBB Region A 32 L. V. Gossick, ED0
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R. Denton, NRR H. L. Ornstein, EDO R. C. DeYoung, NRR J. J. Fouchard, PA R. J. Mattson, NRR N. M. Haller, MPA V. Stello, NRR (MAIL)
NRR J. J. Cumings, 01A R.S.BoyJ,Llfl R. G. Ryan, OSP SS Bldg i 4 R. Minogue, SD H. K. Shapar, ELD W. J. Dircks, NMSS PRELIMINARY NOTIFICATION 1452 329 S
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