ML19246C550
| ML19246C550 | |
| Person / Time | |
|---|---|
| Site: | Fort Saint Vrain  |
| Issue date: | 07/17/1979 |
| From: | Seyfrit K NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| To: | Millen C PUBLIC SERVICE CO. OF COLORADO |
| References | |
| NUDOCS 7907260334 | |
| Download: ML19246C550 (1) | |
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UNITED STATES PDR:HQ E Y,., g ',%i NUCLEAR REGULATORY COMMISSION
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July 17, 1979 Docket No.
50-267 Public Service Company of Colorado ATTN:
Mr. C. K. Iiillen Senior Vice President P. O. Box 840 Denver, Colorado 80201 Gentlemen:
This IE Information Notice is provided as an early m tification 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 tira however licensees should be aware that the NRC is evaluating the issuanc.e of a Bulletin to operating PWR's requesting information on previous inservice inspections of stagnant borated water systens and requesting inspection of systems which have not been inspected recently.
If you have questions or cocaents regarding this matter, please contact the Director of the appropriate NRC Regional Office.
Sincerely,
@WJY r
0-arl V. Seyfrit irector
Enclosures:
1.
IE Information Notice No. 79-19 2.
List of IE Information Notice Issued in 1979 cc:
D. W. Warenbourg, Nuclear Production Manager Fort St. Vrain Nuclear Station P. O.
Box 368 Platteville, Colorado 80651
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L. Brey, Manager, Quality Assurance r
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UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D. C.
20555 IE Information Notice No. 79-19 Date: July 17, 1979 Page 1 of 2 PIPE CRACKS IN STAGNANT E0 RATED WATER SYSTEMS AT PWR PLANTS Description of Circumstances:
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 c37 cal of Stress Corrosion i
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 One 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 IE Circular 76-05 (copy attached) in view of the apparent generic nature of the problem.
During the refueling ortage 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 Stress Corrosion Cracking (lGSCC) originating on the pipe I.D.
The cracking was localized to the heat affected zone where the t37e 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 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 inasmuch as the calculated applied stresses were found to be less than code design limits. There is no conclusive evidenceatthistimetoidentifythpeaggressivechemicalspecieswhich promoted this IGSCC attack.
Further F
' tW Ahis, area and on other system velds are being pursued' DUPLICATE DOCUMENT b
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