ML17252A181
| ML17252A181 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 10/15/1975 |
| From: | Stephenson B Commonwealth Edison Co |
| To: | James Keppler NRC/RGN-III |
| References | |
| BBS Ltr. #692-75 | |
| Download: ML17252A181 (2) | |
Text
-
'Regufatqff.1 BBS Ltr. #692-75 SUBJEX::T:
SUPPLEMENTAL REPORT.TO IErrER CONCERNING EXCESSIVE RUBBER-SEATED VALVES DATED MAY 18, 1972
References:
- 1) Letter from W. P. Worden to Dr. Peter A. Morris dated May 18, 1972
- 2) Letter from W. P. Worden to Mr. J. F. -O'Leary dated December 19, 1973 3~ Letter from B. B. Stephenson to Mr. J. G. Keppler dated October 24, 1974
- 4) Report No. 50-249/75-22 dated August 14, 1975 Report Date:
October 15, 1975 INTRODUCTION In the letter from Worden to Dr. Morris, -Dresden Station reported leakage problems with the seats on rubber-seated valves in the' pressure suppression system.
The letter stated that the station was reviewing this problem to determine the adequacy of the seat material. Until the problem was solved, the station was to local leak-rate test the rubber-seated valves once every three months rather than once per ref'ueling outage.
Four local leak-rate tests are required to check all primary containment rubber-seated butterfly valves for either Unit 2 or 3. The four tests and the corresponding rubber-seated valves are listed in the following table.
Description
- 1. Torus vent relief
- 2. Torus 'Vent relief
- 3. Drywell and torus vent
- 4. Drywell and torus purge Rubber Seated Valves 1601-20A 1601-20B 1601-23, -24, -60, and -63 16o1-21, -22, *and -56 1267S
~
- Mr. James G.~Keppler.er 15, 1975 CORREX::TIVE ACTION A decision was made to change the seat material from*Buna~N rubber *to a rubber compound called "EPr" which can operate at high temperatures.
By the spring of 1973, all the valve seats'. had be~n.changedto the*EPr rubber.
'~
.~
~
This action appeared.ta.* :re.solve *the.* seat.* pr~'biems for the rubber~~eated. ~ai;e~
listed in the first three groups.* Since May, 1972:** the torus vent relief valves and the drywell and torus vent valves have had only three local leak-rate test failures, none of which were due to valve seat failure.
In November, 1973,,
valves 3-160~-23 and -24 exhibited excessive leakages. These failures were attributed to improper operator assembly during maintenance (see letter from Worden to 0 'Leary dated December 1.9, 1973 and letter from Stephenson to Keppler dated October 24, 1974 for further detail). A third :failure occurred in May, 1975 when valve 1601-23 was found with a shaft packing leak (see report no. 50-249/75-22).
Since these three leak-rate test failures were isolated incidents not caused by valve seat deterioration, the testing frequency for the torus vent relief and drywell and torus vent valves will be reduced from once every three months to the original frequency of once per refueling outage.
However, the drywell and tortis purge ;ai~es(1601-21, -22, and -56) will continue to be tested once every three months.
This group of rubber-seated valves has had seven* incidents of excessi \\re leakages **aii.~ to cracked seats within the last two years. These valves are exposed to vaporized nitrogen during drywell inerting, and cryogenic deterioration of the valve seats is the suspected cause of failure.
A plant modification is being engineered to eliminate valve seat failures due to cryogenic stress. The seat problem will be considered resolved if no failures resulting from seat deterioration occur for two years, in which case the testing frequency Will be reduced to once per refueling outage. A follow-up report will be submitted at that time.
. BBS:ELS:smp File/NRC