ML19225C050
| ML19225C050 | |
| Person / Time | |
|---|---|
| Site: | Point Beach  |
| Issue date: | 07/18/1979 |
| From: | James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| To: | Burstein S WISCONSIN ELECTRIC POWER CO. |
| References | |
| NUDOCS 7907260422 | |
| Download: ML19225C050 (1) | |
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JUL 181979 Docket No. 50-266 Docket No. 50-301 Wisconsin Electric Power Company ATTN:
Mr. Sol Burstein Executive Vice President Power Plants 231 West Michigan Milwaukee, WI 53201 Gentlemen:
This Information Notice is provided as an early notification of a possibly significant matter.
It is expected that recipients will 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 you have questions or comments regarding this matter, please contact the Director of the appropriate NRC Regional Office.
Sincerely,
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vJames G. Keppler Director
Enclosure:
IE Information Notice No. 79-19 cc w/ encl:
Mr. G. A. Reed, Plant Manager Central Files Director, NRR/DPM Director, NRR/ DOR C. M. Tremmel, ORB /NRR PDR Local PDR NSIC TIC Sandra A. Bast, Lakeshore Citizens for Safe Encrgy 2) e, 19 0'7 36 0w n t
413 247
UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D. C.
20555 July 17, 1979 IE Information Notice No. 79-19 PIPE CRACKS IN STAGNANT BORATED WATER SYSTEMS AT PWR PLANTS Description of Circumstances:
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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 334 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 oxy 6en 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 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 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 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 Strese 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 were observed at several locations 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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