ML19263E953
| ML19263E953 | |
| Person / Time | |
|---|---|
| Site: | Fort Saint Vrain  |
| Issue date: | 07/26/1979 |
| From: | Seyfrit K NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| To: | Millen C PUBLIC SERVICE CO. OF COLORADO |
| References | |
| NUDOCS 7908060131 | |
| Download: ML19263E953 (1) | |
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July 26, 1979 I)ochet No. 50-267 Public. ;2rvice Company of Colorado ATTN:
- .. C. K. IIllien x alor Vice President P. O.
840 Denver, Colorado 80201 Gentlemen:
The encioned IE Bulletin 79-17 it, foruarded to you for informatica.
No written renponse is required.
Ilowe ve r, the potential corroaton behavior of safety-related systens as it regarda your plant over the.long-tern should be taken into conalderation.
If you desire additional infornation concerning this natter, please contact this offJce.
Sincerely, O
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Seyfrit f)irector Enc losur t. a :
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1.ist of IE Bulletina Issued in Last 12 Montha ec:
D. W. Warenbouta, Nuclear Production llanager l'o r t St. Vrain Nuclear SLation P. O. Box 368 Platteville, Colorado 80651 I.. Brey, llanay,er, Quality Annurance
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7908060 7
UNITED STATES NUCI. EAR 1:EGUIE10i(Y CO1 MISSION OFTICE OF D.sPECTION AND ENFORCEMENT WAS!f1NGTON, D. C.
20555 IE Ihilletin No. 79-17 Date July 26, 1979 Page 1 of 4 PIPE CS G.5 IN STAGNANT BnRATED WATE t SYSTEMS AT PWR PLANTS I)escript ion of Ci rcatances During the period of November 1974 to February 1977 a number of cracking incidents have been experienced in sa fety-related stainlesu steel piping systems and portions of systems which contain oxygenated, stagnant or essentially stagnant borated water.
Met.a llu rg i cal i nve s t. i ga ti on s revealed these c ra cle, occurred in the weld heat af fccted zone of 8-inch to 10-inch type 304 material (nrhedule 10 and 40), initiating on the piping 1.D. surface and propagating in eit her an intergranular or transgranular c. ode typical of St ress Corrosion Cracking.
Analy.415 indicated the probable corrodents to be chloride and oxygen contamination in the affected systems plaats affected up to this time were Arkansan Niclear Unit 1, R E Ginna, lI. D. Robinson Uni' 2, Cryntal itiver Unit 3, San Onofre Unit 1, and Surry Units 1 and 2.
The NRC issued IE Circular 76-06 (copy attached) in view of the apparent generic nature of the problem.
During the refueling outagt of Three flile Island Unit I which began in February of t his year, visual inspections dincioned five (S) through-wall cracks at velds in the spent fuel cooling syatem piping and one (1) at a weld in the decay heat iemoval synten. These cracks were found an a result of local boric acid build-up and later cor.firrred by 1iquid penetrant tents This ini tia l ident.it i ra tion o f cracking was reported to the NRC in a Licennee Event Report (LER) dated May 16, 1979. A preliminary metallurgical analysis was performed by the licensee on a
,wction of cracked and leaking weld joint from the spent fuel cooling system.
The conclusion of this analysis was that cracking was due to Intergranular St re: s Corrosion Cracking (IGSCC) originat.ing on the pipe I.D.
The cracking was localized to the heat. affected zone where the type 304 stainie: s steel is nensitized (precipitated carbides) during welding.
In addition to the main through-wall crack, incipient cracle, were observed at several locations in the weld heat affected zone including the seld root fusion area where a minis. rule lack of fusion had occurred.
The strenses responsible for cracking are believed to be primarily residual welding stresses inasmuch an the calculated applied strences were found to be less than code design limitn.
There is no conclunive evidence at. this time to identify those aggressive chemical species which promoted this IGSCC attack Further analyt ical el fortn in thi: area and on other system welds are being pursued.
DUPLICATE DOCUMENT Entire document previously entered into system under:
ANO 1968626/2,3 No. of pages:
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