ML19259D102
| ML19259D102 | |
| Person / Time | |
|---|---|
| Site: | Zion File:ZionSolutions icon.png |
| Issue date: | 07/26/1979 |
| From: | James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| To: | Brian Lee COMMONWEALTH EDISON CO. |
| References | |
| NUDOCS 7908300392 | |
| Download: ML19259D102 (1) | |
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UNITED STATES I
- ' 7, NUCLEAR REGULATORY COMMISSION
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.. E REGION lli o, -
799 ROOSEVELT ROAD e
GLEN ELLYN, ILLINOIS 60137 JUL 2 61979-
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i 150cket No. 50-295 docket No. 50-304 Commonwealth Edison Company ATTN:
Mr. Byron Lee, Jr.
Vice President P. O. Box 767 Chicago, IL 60690 Gentlemen:
The enclosed IE Bulletin No. 79-17 is forwarded to you for action.
A written response is required.
If you desire additional information regarding this matter, please contact this office.
Sincerely, A
James G. Kepp er Director
Enclosure:
IE Bulletin No. 79-17 cc w/ encl:
Mr. N. Wandke, Plant Superintendent Central Files Director, NRR/DPM Director, NRR/ DOR PDR Local PDR NSIC TIC Mr. Dean Hansell, Office of Assistant Attorney General 7N8s oo3r>.
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e UNITED STATES NUCLEAR REGULATORY COMMISSION "c5 LWRP3.T.Tili'"E"'
W July 26.", 1979-e IEBulletin!No.79-17 i
PIPEICRACKS IN STAGNANT BORATED WATER SYSTDIS AT PWR PLANTS Descfiption of Circumstances:
During the period of November 1974 to February 1977 a number of cracking incidents have been experienced in safety-related stainless steel yiping 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, B.B. Robinson Unit 2, Crystal River Unit 3, San Onofre Unit 1, and Surry Units 1 and 2.
The NRC issued Circule 76-06 (copy attached) in view of the apparent generic nature of the problem.
During the refueling outage of Three Mile sland 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 piping and one (1) at a weld in the decay heat removal system. These cracks were found as a result of local boric acid build-up and later confirmed by liquid penetrant tests. This inicial 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 beat affected zone where the type 304 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 veld heat affected zone including the veld 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 1GSCC attack. Further analytical efforts in this area and on other system welds are being pursued.
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