ML19263E952
| ML19263E952 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 07/26/1979 |
| From: | Seyfrit K NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| To: | Cavanaugh W ARKANSAS POWER & LIGHT CO. |
| References | |
| NUDOCS 7908060123 | |
| Download: ML19263E952 (1) | |
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July 26, 1979 Dochet. f;on.
50-113 50-368 Arkan..ii Power atu! I,1411t Cornpriny AT fli:
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L'on 551 I,Lttle Rock, Arhannan 72203 Gentlenan:
'f h e enuloned IE lhtlletin 79-17 15 f oru.t rded t o you for action. A written r e spom.+- 15. required.
If you dentro additional inforuation regardind thir.
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UNITED STATES Nl! CLEAR REGULATORY C0!1tlISS10N OFFICE OF INSPECTION AND ENFORCEMENT WAS!!INGTON,
D. C.
20555 lE Bulletin No. 79-17 Date July 26, 1979 Page 1 of 4 PIPE t%3 IN STAGNANT 1:0 HATED WATER SYSTEt!S AT PWR PLANTS Descript; a of Circumstances:
During th peri.od of Nov"mber 1974 to February 1977 a number of cracking incidents have been experienced in safety-related stainless steel piping systems ar.d portions of systems which contai.n oxygenated, stagnant. or essentially itagnant borated water.
Metallur;;ical investigations revealed these cracIn.
occurred in the weld heat af f ected zone of 8-inch to 10-inch t ype 304 material (schedule 10 and 40), initiating on the piping 1.D. surf ace and propagating in either an intergranular or transgranular mode typical of Stress Corrosion C ra c k i n g.
Analysis indicated the probable corrodents to he chloride and oxygen c ontam ina t. i o n in the affected systems.
Plant.s a f fected up to this time were Aikansas Nuclear Unit 1, R.
F..
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 76-06 (copy attached) in view of the apparent generic nature of the problem.
During the refueling out. age 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 syst em.
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 (IGSCC) originat.ing on the pipe I.D.
The cracking was localized to the heat af fected zone where the type 304 stainless steel is sensitized (precipitated carbides) during welding In addition to the nain 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 inasmuch as the calculated applied stresses were found to be less than code design limits There is no conclusive evidence at this time to ident.i fy those aggressive chemical species which promoted this IGSCC attack.
Further analytical efforts in this area and on other system weldr. are being pursued.
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