ML17252B152
| ML17252B152 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 01/31/1978 |
| From: | Stephenson B Commonwealth Edison Co |
| To: | James Keppler NRC/RGN-III |
| References | |
| BBS Ltr. #692-85, BBS LTR: 78-105, IR 1975022 | |
| Download: ML17252B152 (2) | |
Text
e.
e Commonwealth Edison Dresden Nuclear Power Station R.R. #1 Morris, Illinois 60450 Telephone 615/942-2920 BBS LTR:
78-105 January 31, 1978 Mr. James G. Keppler, Regional Director Directorate of Regulatory Operations - Region III
- .,.U.S. Nuclear Regulatory Commission 799 Roosevelt Road Glen Ellyn, IL 60137
SUBJECT:
. Follow-up Report to Letter Concerning Excessive leakage Through Rubber-seated Valves
REFERENCES:
- 1)
BBS Letter #692-75
- 2)
Report No. 50-249/75-22 Dated August 14, 1975
Dear Hr. Keppler,
In the referenced BBS Letter #692-75, Dresden Station reviewed leakage problems with four groups of rubber-seated valves.
Changing the seat material resolved the problems for three of the valve groups.
The fourth valve group, the drywell and torus purge valves, however, displayed excessive leakage as a result of cracked seats on several subsequent occasions.
These valves were exposed to liquid nitrogen during drywell inerting and cryogenic deterioration of the valve seats was the suspected cause of failure.
Until plant modifications could be engineered to eliminate valve seat failure due to cryogenic stress, it was decided that the drywell and torus 1601-21,-22,-55, and -56 purge valves would be tested for local leakage once every three months rather than once each refueling outage.
This increased testing interval was to be con-tinued until no failure resulting from seat deterioration had occurred for two years, at which time the testing frequency would be returned to once per refueling outage.
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The final corrective action consisted of two parts:
(1) disc<?!'!t~~u~_9. __ ~_se __ Qf __ a_manuaL bypass line- -
*--1n elie-*nitrc>"g-en-fnerting line, and (2) stationing an operator at the nitrogen inerting line to verify that the temperature does not fall below that limit required to maintain nitrogen in a gaseous state.
This corrective action ensured that the drywell and torus purge valves would not be exposed to liquid nitrogen during drywell inerting.
Subsequent local leak rate testing of the valves in question has demonstrated that a failure due to seat deterioration last occurred on 10/07/75 (valve 1601-22 on U2).
Because no local leak rate test failures resulting from seat deterioration have occurred for at least two years, the seat problem is considered resolved.
Therefore, the testing frequency of these valves is being reduced from once every three months to once per refueling outa~e.
~
BBS:DS:av cc:
B. Shelton D. Farrar M.S. Turbak File/NRC
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/-'"--B. B.
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- Station Superintendent Dresden Nuclear Power Station