ML19225C037
| ML19225C037 | |
| Person / Time | |
|---|---|
| Site: | 05000484 |
| Issue date: | 07/18/1979 |
| From: | James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| To: | Dienhart A NORTHERN STATES POWER CO. |
| References | |
| NUDOCS 7907260407 | |
| Download: ML19225C037 (1) | |
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UNITED STATES Tic
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GLEN ELLYN. lLLINOIS 60137 JUL 181973 Docket No. 50-484 Northern States Power Company ATTN:
Mr. A. V. Dienhart Vice President - Tyrone Energy Park 100 North Barstow Street Eau Claire, WI 54701 Gentlemen:
Thir Information Notice is provided as an earl'. notification of a possibly significant matter.
It is expected that recipients wf11 review the infor-mation 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 PWR's requesting infor-mation on previous inservice inspections of stagnant borated water systems and requesting inspection of systems which have not been inspected recently.
If yvu have questions or comments regarding this matter, please contact the Director of the appropriate NRC Regional Of fice.
Sincerely,
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James G.
ler Director
Enclosure:
IE Information Notice No. 79-19 cc w/ encl:
Central Files Director, NRR/DPM Director, NRR/ DOR PDR Local PDR NSIC TIC Regions I 6 IV 413 052 D
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7907260407
UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D. C.
20555 July 17, 1979 IE Information Not ce No. 79-19 PIPE CRACKS IN STAGNANT BORATED WATER SYSTEMS AT PWR PLANTS Description of Circumstances:
During the period of Nove=ber 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 Cracking. Analysis indicated the probable corrodents to be chloride and oxygen contamination in the affected systems. 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 problem.
During the refueling outage of 'Ihree Mile Island Unit I which began in February of this year, visual inspections disclosed five (5) through-wall cracks at welds in the spent fuul cooling system piping and one (1) at a weld in the decay heat removal system. These cracks were fcund as a result of local boric 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 preliminary metallurgical analysis was performed by the licensee on a section of cracked and leaking weld joint from the spent fuel cooling system.
The conclusion 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 304 stainless steel is sensitized (precipitated carbides) during welding.
In addition to the main through-wall crack, incipient cracks wee observed at several locaticns in the weld heat affected zone including the weld root fusion area where a miniscule lack of fusion had occurred. The stresses responsible for cracking are believed to be primarily residual welding stresses in as much as the calculated applied stresses were found to be less than code design limits. There is no conclusive evidence at this time to identify those aggressive chemical species which promoted this IGSCC attack. Further analytical efforts in this area and on other system welds is being pursued.
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