ML19338D007
| ML19338D007 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 04/07/1971 |
| From: | Hoyt H COMMONWEALTH EDISON CO. |
| To: | |
| References | |
| NUDOCS 8009150603 | |
| Download: ML19338D007 (2) | |
Text
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Commonwealth Edison Company O Pi E P' I R S T NATBONAL PLAZA CHlCAGO.
ILLINOIS as+.n n.oi, n.
POST OFFICE SON 767
- C M I C A G O.
ELLINOIS 40490 j
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Dresden Nuclear Power Station 2
R.R.#1 Morris, Illinois 6C450 A'
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April 7, 1971
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C9 Dr. Peter A. Morris, Director k
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/(N U.S. Atomic Energy Commission ushington, D.C.
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SUBJECT:
LICENSE DPR-2, DRESDEN NUCLEAR PO'JER STATION UNIT dl
Dear Dr. Morris:
This is to report a condition relating to the operation of the station in which on March 11, 1971, one of the four primary drum lou level scram relays failed.
PROBLEM, INVESTIGATION, AND CORRECTIVE ACTION On March 11, 1971, Unit 1 was operating at 140 M.le with steady state conditions.
At 9:30 AM a fuse connected to the primary drum level scram relay blew resulting in a trip of the "A" safety system. No abnormal conditions were noted after the fuse was replaced and the safety system was reset.
A burning odor was detected by the reactor operator at 10:30 AM and a subsequent investigation of the safety system relay board revealed that the same primary drum level scram relay fuse had blown again.
The relay contacts were still closed and the protective glass cover was coated with a brownish film.
Because the "A" safety system had not tripped, as it should have, at 11:00 9! the fuse in second primary drum low level scram relay in the "N' safety system. was pulled to trip the "A" safety system.
This was accomplished to place the unit's operation in the most conservative operating conditica until the fculty relay could be replaced.
By 1:10 PM the failed relay had bean replaced and the safety system reset, returning the plant operation to normal.
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Dr. Peter A. Morris Page 2-
. April 7, 1971 4
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Subsequent evaluation of the event and examination of the faulty relay indicated the relay coil had shorted and the insulating material, having become soft and tacky, had fallen on the relay contacts holding them in the closed position.
This prevented the safety system from tripping when the fuse blew.
i This is the first known failure of this type in the ten years of operation of Dresden 1 and it is felt that the probability of this type of failure is small. Also, the circuit design anticipated the possibility of a l
relay failure by providing redundant relays and therefore no further action is planned.
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Sincerely, i
M'/.
H.K.Hoyt Superintendent HRH:rh i
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