ML19274G207
| ML19274G207 | |
| Person / Time | |
|---|---|
| Site: | 05000484 |
| Issue date: | 07/26/1979 |
| From: | James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| To: | Dienhart A NORTHERN STATES POWER CO. |
| References | |
| NUDOCS 7908300422 | |
| Download: ML19274G207 (1) | |
Text
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UNITED STATES g
NUCLEAR REGULATORY COMMISSION 8V 3.,, g' n
"'4 c E REGION 111 6
o, 799 ROOSEVELT ROAD 8
o GLEN ELLYN. ILLINOIS 60137 jut. 2 619J9 Docket No. 50-484 3
Sorthern States Power Company 4TTN:
Mr. A. V. Dienhart Vice President - Tyrone Energy Park 100 North Barstow Street Eau Claire, WI 54701 Gentlemen:
The enclosed IE Bulletin Fa. 79-17 is forwarded to you for information.
No written response is rr. quired. However, the potential corrosion be-havior of safety relate.: systems as it regards your plant over the lona term should be taken into consideration.
If you desire additional information concerning this matter, please contact this office.
Sincerely,
{},.. A PJames G. Ke-er Director
Enclosure:
IE Bulletin No. 79-17 cc w/ encl:
Central Files Director, NRR/DPM Director, NRR/ DOR PDR Local PDR NSIC TIC 9q7 LUdj 1AQ Regions I & IV J 4 l' 79083 00 %g
UNITED STATES NUCLEAR REGUIATORY COMMISS!ON mcNLMW'3.^P EgggmET a
July 26.', 1979'-*
Y.
e a-IE Bulletin.No. 79-17 PIPE CRACKS IN STAGNANT BORATED WATER SYSTDiS AT PWR PLANTS Dese iption 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. Cinna, B.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.
Daring the refueling outage of Three Mile Island Unit I which began in February of this year, visual inspections disclosed five (5) through-vall 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 veld joint from the spent fuel cooling system.
The conclusion of this analysis was that cracking was due to Intergranular Stress Corrosion Crack.tng (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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