ML19247A638
| ML19247A638 | |
| Person / Time | |
|---|---|
| Site: | Limerick  |
| Issue date: | 07/17/1979 |
| From: | Grier B NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| To: | Boyer V PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC |
| References | |
| NUDOCS 7908010521 | |
| Download: ML19247A638 (1) | |
Text
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[ata a'%,k' 'g UNITED STATES E
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NUCLEAR REGULATORY COMMISSION
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E REGION 1 0, ' ?* e 631 PARK AVENUE k, ' V
,o KING OF PRUSSI A, PENNSYLVANI A 19406 Docket Nos. 50-352 50-353 JUL 17 MS Philadelphia Electric Company ATTN:
Mr. V. S. Boyer Vice President Engineering and Research 2301 Market Street Philadelphia, Pennsylvania 19101 Gentlemen:
This Information Notice is provided as an early notification of a possibly significant matter.
It is expected that recipients will review the information for possible applicability to their facilities.
No response is requested at this time however licensees should be aware that the NRC is evaluating the issuance of a Bulletin to operating PWR's requesting information on previous inservice inspections of stagnant borated water systems and requesting inspection of systems which have not been inspected recently.
If you have questions or comments regarding this matter, please contact the Director of the appropriate NRC Regional Office.
Sincerely, eg Bo ce H. Grier Director
Enclosures:
1.
IE Information Notice No. 79-19 2.
List of Information Notices Issued in 1979 E75272 7 908010 W
UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D. C.
20555 IE Information Notice No. 79-19 Date:
July 17, 1979 Page 1 of 2 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 cracking incidents have been exNrienced 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 occurrec' in the weld ncit affected zone of 8-inch to 10-inch type 304 material (schedu~
10 and 40), initMting on the piping I.D. surface and propagating in either an intergrarular or transgranular mode typical of Stress Corrosion Cracking.
Analysis indicated the probable corrodents to be chloride and oxygen contamin-ation in tne 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 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 cricked and leaking weld joint from the spent fuel cooling system.
The conclusion of this analysis was that cracking was due to Intergranular Stress Corr sion Cracking (IGSCC) originating on the pipe I.D.
The cracki.1g 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 is being pursued.
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