ML19289G278
| ML19289G278 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 07/26/1979 |
| From: | Grier B NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| To: | Herbein J METROPOLITAN EDISON CO. |
| References | |
| NUDOCS 7908100233 | |
| Download: ML19289G278 (1) | |
Text
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UNITED STATES f,,
NUCLEAR REGULATORY COMMISSION y
3-E REGION 1
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July 26, 1979 Docket Nos. 50-289 50-320 Metropolitan Edison Company ATTN: Mr. J. G. Herbein Vice President - Generation P. O. Box 542 Reading, Pennsylvania 19640 Gentlemen:
The enclosed Bulletin 79-17 is forwarded to you for information.
No written response is required. However, the potential corrosion behavior of safety related systems as it regards your plant over the long term should be taken into consideration.
If you desire additional information concerning this matter, please contact this office.
Sincerely, kf Boyce H. Grier Director
Enclosures:
1.
IE Bulletin No. 79-17 with Attachments 2.
Listing of IE Bulletins Issued in Last 12 Months cc w/encls:
E. G. Wallace, Licensing Manager J. J. Barton, Project Manager R. C. Arnold, Vice President - Generation L. L. Lawyer, Manager - Generation Operations G. P. Miller, Manager - Generating Station - Nuclear J. L. Seelinger, Unit 1 Superintendent W. E. Potts, Unit 1 Superintendent - Technical Support J. B. Logan, Unit 2 Superintendent 2))4 g G. A. Kunder, Unit 2 Superintendent - Technical Support I. R. Finfrock, Jr.
Mr. R. Conrad G. F. Trowbridge, Esquire Miss Mary V. Southard, Chairman, Citizens for a Safe Environment 7008100235
/ t' ENCLOSURE 1 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D. C.
20555 IE Bulletin No. 79-17 Date: July 26, 1979 Page 1 of 4 PIPE CRACKS IN STAGNANT B0 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 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 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 syctem piping and one (1) at a weld in the decay heat removal system.
These cracks were found as a result of local boric acid buildup 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 perfonned 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 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 are being pursued.
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