ML19247A581
| ML19247A581 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 07/17/1979 |
| From: | Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| To: | Johari Moore SOUTHERN CALIFORNIA EDISON CO. |
| References | |
| NUDOCS 7908010392 | |
| Download: ML19247A581 (1) | |
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UNITED STATES
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1990 N. CALIFORNI A BOULEV ARD
, 'b SUIT E 202, WALNUT CR E E K PL AZA WALNUT CR EEK, CAltFORNI A 94596 July 17,1979 Docket Nos. 50-361 50-362 50-206 Southern California Edison Company P. O. Box 800 2244 Walnut Grove Rosemead, California 91770 Attention: Mr. J. B. Moore Vice President Gentlemen:
This infomation 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 inspected recently.
If you have questions or comments regarding this matter, please contact the Director of the appropriate NRC Regional Office.
Sincerely, R. H. Engelken Director
Enclosure:
IE Information Notice No. 79-19 cc w/ enclosure:
J. H. Drake, SCE
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J. M. Curran, SCE J. T. Head, SCE Ex,,-01,m--<0 790801037 1
UNITED STATES NUCLEAR REGULATORY CO! MISSION OFFICE OF INSPECTION AND ENFCRCEMENT WASHINGTON, D. C.
20555 July 17, 1979 IE Infomation Notice No. 79-19 PIPE CRACKS IN STAGNANT BORATED WATER SYSTEMS AT PWR PLANTS Description of Circunstances:
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 304 material (schedule 10 and 40), initiating on the piping I.D. surface and propagating in either an intergranular or transgranular mode typical of Stress Corrosion C racking. Analysis indicated the probable corrodents to be chloride and oxygen contanination in the affected systens.
Plants affected up to this time were Arkansas Nuclear Unit 1, R. E. Ginna, H.B. Robinson Unit 2, Crystal River Unit 3, San Onofre Unit 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 refueling outage of Three Mile Island Unit I which began in February of this year, visual inspections disclosed five (5) through-wall cracks at welds in the spent fuel cooling system pioing and one (1) at a weld in the decay heat removal system. These cracks were fcund as a result of local beric acid build-up 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 16, 1979. A prelininary metallurgical analysis was performed by the lice.1see en a section of cracked and leaking weld joint from the scent fuel ccoling ;vstem.
The conclusien of this analysis was that cracking was due to Intergranular Stress Corrosion Cracking (IGSCC) originating on the pipe I.D.
The cracking was localized to the heat affected zone where the type 3C4 stainless steel is sensitized (precipitated carbides) during welding.
In addition to the main through-wall crack, incipient cracks were observed at several locations in the weld heat affected zone including the weld root fusion area whera a miniscule lack of fusion had cccurred. The stresses responsible for cracking are believed to be prirarily residual welding stresses in as much as the calculated applied stresses were found to be less than code design linits. There is nu conclusive evidence at this tire to identify those aggressive chemical species which prenoted this IGSCC attack.
Furtha" aralvtical efforts in this area and on other system welds is being purst
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