ML19247A582
| ML19247A582 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 07/17/1979 |
| From: | Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| To: | Mattimoe J SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| References | |
| NUDOCS 7908010394 | |
| Download: ML19247A582 (1) | |
Text
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SUITE 202, WALNUT CREEK PLAZA e.
WALNUT CREE K, CALIFORNIA 94596 July 17, 1979 Docket No. 50-312 Sacramento Municipal Utility District P. O. Box 15830 Sacramento, California 95813 Attention: Mr. John J. Mattimoe Assistant General Manager Gentlemen:
This infonintion 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 coments 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 s
cc w/ enclosure:
R. J. Rodriguez, SMUD L. G. Schwieger, SMUD s
id,2f;I"O nd) 76080103D
UNITED STATES NUCLEAR REGULATORY COM'iISSICN OFFICE OF INSFECTION AND ENFCRCE"ENT WASHINGTON, D.C.
20555 July 17, 1979 IE Infornation Notice No. 79-19 PIPE CRACKS IN STAGNANT 80 RATED WATER SYSTEMS AT PWR PLANTS Description of Circumstances:
During the pericd 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 naterial (schedule 10 and 40), initiating on the piping I.C. surface and propagating in either an intergranular or transgranular mcde typical of Stress Corrosion C racki ng.
Analysis indicated the probable corredents 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.S. Robinson Unit 2, Crystal River Uni r 3, San Gnofre 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 Februt y of this year, visual inspections disclosed five (5) through-wall cracks at w ids in the spent fuel coolire system piping and one (1) at a weld in the decay h.at removal system. These cracks were found as a result of local boric acid build-up and later confin ed 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 prelininary metallurgical analysis was performed by the licensee en a section of cracked and leaking weld joint from the scent fuel cooling systen.
The conclusion of this analysis was that cracking was due to Intergranular SP ess Cerrosion Crackinc (IGSCC) criginating on the pi:e I.D.
The cracking was localized to the heat affected zone where the ty;e 304 stainless steel is sensi':ized (precipitated carbides) durir.g welding.
In addi-ion to the rain through-wall crack, incipient cracks were cbserved at several locations in the weld heat affected zone including the weld rcot fusion area where a mini cule lack of fusion had occurred.
The stresses responsible for cracking are bel:eved to be prirarily residual welding stresses in as ruch as the calculated appif ed stresses were found to be less than ccde design linits.
There is no conclusive evidence at this tire to identify those aggressive chemical scecies which prcroted this IGSCC attack.
Further analytical efforts in this area and cn 7""
other system welds is being pu
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