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ReTrulatory gg Commonwealth Edison Company ON: rins? NATIONAL PLAZA
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Mr. D.'J. Skovholt Mhh.18i973 *
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Directorate of Licensing (N
U.S. Atomic Energy Commission N
Washington, D.C.
20545
Subject:
Review of Dresden and Quad-cities Stations
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for Control Circuit Deficiencia-
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Dkts 50-10, 50-237, 50-249, M -2b43tnd 50-265 v
Dear Mr. Skovholta j
Your letter of December 22, 1972, requested that Dresden and Quad-Cities Stations control circuit design be reviewed for possible deficiencies.
The review has been completed for Dresden Units 2 and 3 and Quad-Cities Units 1 and 2 and the results are discussed below.
The review of Dresden Unit 1 is presently underway and a report will be submitted by May 1, 1973.
Results of Design Review This design review has resulted in disclosure of design deficiencies in several systems.
The design deficiencies are similar in nature to the problems encountered in the Standby Gas Treatment and the Standby Liquid Control Systems at Oyster Creek.
Following are brief descriptions of the design deficien-cies found in the circuit review.
1.
Standby Liquid Control System The circuitr.y employed in this system is similar to that found at Oyster Creek, and, therefore, the problem is identical.
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Commonwealth Edison Company Mr. D. J. Skovholt March 7, 1973
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2.
Standby Gas Treatment System (SGTS) t Circuit analysis indicates that a damper, which would
'normally isolate the turbine room from the SGTS for an accident, would remain open if the related SGTS fan circuit breaker la " racked out" while the alternate SGTS train is responding to an accident signal.
This would result in loss of secondary containment.
The problem here is similar to the problem encountered at Oyster Creek where a fan circuit breaker "b" contact is used to control damper position.
When the circuit breaker is "rakced out", the "b" contact is lost to the close control circuit of the damper contactor and the damper assumes an open position.
3.
Engineered Safeguard Buses Dresden Unit 2 Bus 28 and 29 Dresden Unit 3 Bus 38 and 39 Quad-Cities Unit 1 Bus 18 and 19 Quad-Cities Unit 2 Bus 28 and 29 The circuitry for the Bus Tie (BT) circuit breaker j
which ties these buses (e.g., bus 28 tb bus 29) together is such that if either of the main feed circuit breakers (i.e., bus 18 or 19 main feed breakers) is " racked out" withthe BT breaker open, the BT breaker cannot be closed electrically.
The main feed breaker "b"
contacts are connected in the BT breaker close circuit.
When one main feed breaker is closed and the main feed breaker to the other bus is " racked out", the close circuit for the BT is open. and the BT breaker cannot be closed electrically.
4.
Engineered Safeguard Buses Quad-Cities Unit 1 Bus 18/19-5 Quad-cities Unit 2 Bus 28/29-5 1
Commonwealth Edison Company Mr.'D. J. Skovholt March 7, 1973
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Bus 18/19-5 is supplied from bus 18 or bus 19.
Bus 28/29-5 is supplied.from bus 28 cc boa 29.
The control circuits for these two bussea is identical.
For this narrative, consid'er bus 18/19-5'.
If the main feed breaker for bus 18/19-5 frem bus 18 is closed, then the main fdsd breaker to bus 18/19-5 from bus 19 cannot be closed.
The "b" contacts on the main feed breakers interlock their~close circuits such that only one main feed breaker can be closed at anytime.
When a main feed breaker to bus 18/19-5 is " racked out",
the "b" contact for that breaker is lost and the close circuit for the remaining nain ' feed breaker is open.
In this case, bus 18/19-5 cannot be energized.
5.
Diesel Generator Auxiliaries l
Dresden Diesel Generator 2/3 Quad-Cities Diesel Generator 1/2 The " swing" diesel generators at Dresden and Quad-Cities have two sources of power for their cooling' water pumps, oil transfer pumps and vent fans.
One source of power is from one unit's safeguard bus and the second source of power is from the second unit's safeguard bus.
The controls for these auxiliaries are interlocked with breaker "b"
contacts such that both supply breakers cannot be. closed simultaneously.
If one breaker is " racked out", its "b" contact in the remaining breakers close circuit is lost and the remaining breaker cannot be closed electrically.
Therefore, if one breaker to any one of these auxiliaries is " racked out", that auxiliary is not available.
Corrective Action The corrective action to be taken in order to overcome these circuit deficiencies is as follows:
1.
For the short term, while circuit ilesign is 'being accomplished, administrative controle, will be initiated at Dresden and Quad-Cities to temporarily overcome these circuit deficiencies.
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1 C o.mmonwealth Edison CompanyI z
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.Mr.
D.'J. Skovholt-March 7, 1973 f
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For the long term, circuit design will be changed which will not permit a " racked out" breaker to influence the close circuit of a related breaker in the manner described.
'chedule.
S The short term corrective action will'be initiated inanediately and the long term corrective action will be installed by January, 1974.
The. plant procedures for' removing' redundant' safety
. systems from service are presently being reviewed to determine.
the best method for performing surveillance a*s requested.in your letter of December 22,197'.
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one signed original and 39 copies of this letter are provided for your use.
Very truly
- ours, C
Anan d
Byrbn Lee, Jr.
Assistant to the President L
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