ML19256B556
| ML19256B556 | |
| Person / Time | |
|---|---|
| Site: | McGuire, Mcguire  |
| Issue date: | 07/26/1979 |
| From: | James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| To: | Parker W DUKE POWER CO. |
| References | |
| NUDOCS 7908070741 | |
| Download: ML19256B556 (2) | |
Text
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101 M ARIE T T A ST, N W, SulT E 3100 G.,
A AT L ANT A. GE ORGI A 30303
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,cf jb6 2 f 1979 In Reply Pefer To:
RII:JPO 50-369 "
(' 50-370 Duke Power Company ATTN:
W. O. Parker, Jr.
Vice President, Steam Production P. O. Box 33189 Charlotte, NC 28242 Centlemen:
No The enclosed Bulletin 79-17 is f orwarded to you for informatior..
written response is required.
However, the potential corrosion beha-vior 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.
S inc erely,
- } ; \\.,,.
Jam'es P. O'Reilly
~
ry Director
Enclosure:
' M8070 >g
JUL z 61570
. Duke Power Company cc w/ encl:
M. D. McIntosh, Project Manager Post Office Box 488 Cornelius, North Carolina 28031 J. C. Rogers, Project Manager Post Office Box 33189 Charlotte, North Carolina 28242 J. E. Smith, Station Manager Post Office Box 1175 Seneca, South Carolino 29676
UNITED STATES NUCl. EAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D. C.
20555 July 26, 1979 IE Bulletin No. 79-17 PIPE CRACKS IN STAGNANT BORATED WATER SYSTEMS AT PWR PLANTS Description of Circumstances:
During the period of November 1974 to February 1977 a number of cricking 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 1.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 contami-nation 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 Onotre 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 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 I ti, 1979. A preliminary metallurgical analysis was performed by the licensee on section of cracked and leaking weld joint from the spent fuel cooling system.
aThe 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 ef forts in this area and on other system welds are being pursued.
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