ML20084N833

Supplemental AO 50-249/75-22:plant Mod Being Initiated to Eliminate Valve Seat Failures Due to Cryogenic Stress

ML20084N833
Person / Time
Site:	Dresden
Issue date:	10/15/1975
From:	Stephenson B COMMONWEALTH EDISON CO.
To:	James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML17194B579	List: ML20084N833
References
692-75, NUDOCS 8306090090
Download: ML20084N833 (2)

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. m Commo nlth Edison One First National Plaza. Chicago, I'linois l C

.. (Q', / Address Reply Chicago, Ilknoisto: Post Othee Box 767 60690 BBS Ltr. //692-75 Dresden Nuclear Power Station R. R. h1 Morris, Illinois 60450 October 15, 1975 ,

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.7 Mr. James G. Keppler, Regional Director /yk/d - D-Directorate of Regulatory Operations-Region III  ; q.y ,.,

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SUBJECT:

SUPPLt??!TAL REPORT TO LETTER CONCERMING EXCESSIVE LF12dGPS.THROUGH  ?

rut?ER-SEATED VALVES DATED IaY 18, 1972 l

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References:

1) Letter from W. P. Worden to Dr. Peter A. Morris dated May 18, 1972  !

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2) Letter from W. P. Worden to-Mr. J. F. O' Leary dated A December 19, 1973

3) Letter from B. B. Stephenson to Mr. J. G. Keppler dated October 24, 1974 i

4) Report No. 50-249/75-22 dated August 14, 1975

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Report Date: October 15, 1975 i

i 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 refueling 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.

Descrio+. ion Rubber Seated Valves

1. Torus vent relief 1601-20A

2. Torus vent relief 1601-20B 3 Drywell and torus vent 1601-23, -24, -60, and -63 4 Drywell and torus purgo 1601-21, -22, and -56 8306090090 750814 12678' PDR ADOCK 05000249 S pop COP ( SENT REGION _

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Mr. Jamla G. Edpplc '

October 15, 1975 CORRECTIVE ACTION A decision was made to change the seat material from Euna-N rubber to a rubber compound called " EPI" which can operate at high temperatures. By the spring of 1973, all the valve seats had been changed to the EPT rubber.

This action appeared to resolve the seat problems for the rubber-seated valves 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, nsne of which were due to valve seat failure. In November, 1973 valves 3-1601-23 and -24 exhibited excessive leakages. These failures were attributed to improper operator assembly during maintenance (see letter from Worden to O' Leary dated December 19, 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. SG-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 d /well and torus purge valves (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 excessive leakages due 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 modificatien 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.

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B. .Ste[nenson Superintentent BBS:ELS:sep File /IEC

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