ML19247A579
| ML19247A579 | |
| Person / Time | |
|---|---|
| Site: | Humboldt Bay, Diablo Canyon |
| Issue date: | 07/17/1979 |
| From: | Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| To: | Crane P PACIFIC GAS & ELECTRIC CO. |
| References | |
| NUDOCS 7908010389 | |
| Download: ML19247A579 (1) | |
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UNITED STATES
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NUCLEAR REGULATORY COMMISSION 7J'
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1990 N. CALIFORNI A BOUL EVARD
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d' SUITE 202, WALNUT CREEK PLAZA
- ,,,a WALNUT CR E E K, CALIFORNIA 94596 July 17, 1979 Docket Nos. 50-133 50-275 50-323 Pacific Gas and Electric Company 77 Beale Street San Francisco, California 94106 Attention: Mr. Philip A. Crane, Jr.
Assistant General Counsel Gentlemen:
This information Notice is provided as an early notification of a possibly significant matter.
It is expected that recipients will review the information for possible applicability to their facilities.
No response is requested at this time, however, licensees should be aware that the NRC is evaluating the issuance of a Bulletin to operating PWRs requesting information on previous inservice inspections of stagnant borated water systems and requesting inspec-tion of systems which have not been inspectid recently.
If you have questions or comments regarding this matter, please contact the Director of the appropriate NRC Regional Office.
Sincerely, L
a.L S-R. H. Engelken Director Encicsure:
IE Information Notice No. 79-19 s
cc w/ enclosure:
W. Barr, PG&E s
W. A. Raymond, PG&E N
R. Ramsey, PG&E 4<M E. Weeks, PG&E, Humboldt Bay 15302 O^
J. D. Worthington, PG&E N
7908010 Y f
UNITED SiATES NUCLEAR REGULATORY CO MISSION OFFICE OF INSPICTION AND ENFORCET'ENT WASHINGTON, D.C.
20555 July 17, 1979 IE Infomation Notice No. 79-19 PIPE CRACKS IN STAGNANT B0 RATED WATER SYSTE?iS AT PWR PLANTS Description of Circumstances:
During the period of November 1974 to February 1977 a number of cracking incidents have been experienced in safety-related stainless steel piping systems and portions of systems which contain oxygenated, stagnant or essentially stagnant borated water. Metallurgical investigations revealed these cracks occurred in the weld heat affected zone of 8-inch to 10-inch type 3C4 raterial (schedule 10 and 40), initiating on the piping I.C. surface and propagating in either an intergranular or transgranular mode tyoical of Stress Corrosion Cracking. Analysis indicated the probable corrodents to be chloride and oxygen contamination in the affected systems.
Plants affected up to this time were Arkansas Nuclar Unit 1, R. E. Ginna, H.B. Robinson Unit 2, Crystal River Unit 3, San Onofre Un"- 1, and Surry Units 1 and 2.
The NRC issued Circular 76-06 (copy attached) in view of the apparent generic nature of the problen.
During the reCeling outage of Three Mile Island Unit 1 which began in February of this year, visual inspections disclosed fiva (5) through-wall cracks at welds in the spent ' Jel cooling systen piping and one (1) at a weld in the decay heat removal systen. These cracks were found as a result of local boric acid build-uc and later confirmed by liquid penetrant tests.
This initial identification of cracking was reported to the NRC in a Licensee Event Report (LER) dated May 15, 1979. A prelinicary etallurgical analysis was ;erformed by the licensee on a section of cracked and leaking neld joint frcn the scent fuel cooling system.
The conclusien of this analysis was that crackinq.sas due to Intercranular Stress Corrosion Cracking (IGSCC) originatirg en the pije :.0.
The cracking was localized to the hea; affected cne where the type 3X stainless steel is sensitizec (pra:ip# tated cc.rbides) during v.elcing.
In addition to the main thecuch-wall crack, incioient cracks were observed at several lccations in the weld heat affected 2cne including *he weld rect fusion area shere a niniscule lack of fusicn had occurred.
The stresses responsible for cracking are believed to be prirar ly residual welding stresses in as much as the calculated applied stresses were found to be 'ess that, code design lic.i ts.
These is no conclusive evidence at this tire to identi'j thcse aggressive chenical species which premeted this IGSCC attac's.
Furtbe analytical efforts in this area ar.d on other system welds is being pursued.
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[ gig r-I Entire document previously entered into system under:
ANO 7907 30/6 C/
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