ML17238A736
| ML17238A736 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 04/25/1972 |
| From: | Worden W Commonwealth Edison Co |
| To: | Morris P US Atomic Energy Commission (AEC) |
| References | |
| Download: ML17238A736 (3) | |
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50-237 Commonwealth Edison Q?-2~
Company 0 N E FI R.S T N AT I 0 NA L PLAZA
- CH I ~AG 0, I LL I N 0 I 8 Addrou Reply lo, POST OFFICE BOX 767 *CHICAGO, llllNOIS 60690 Dr. Peter A. Morris, Director Division of Reactor Licensing U.S. Atomic Energy Commission Washington, D.C.
20545 Dresden Nuclear Power Station R. R. Ill Morris, Illinois 60450 April 25, 1972
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SUBJECT:
LICENSE DPR-25, DRESDEN NUCLEAR POWER STATION, UNIT 113._ SECTION 6.6.C.l OF THE TECHNICAL SPECIFICATiONS, AND LICENSE DPR-19, DRESDEN NUCLEAR POWER STATION, UNIT 112, SECTION 6.6.C.l OF THE TECHNICAL SPECIFICATIONS.
Dear Dr. Morris:
This,is to report a condition relating to the operation of the plant when, a switching problem on bus 28 rendered the "A" standby gas train, 2A standby liquid control pump, and the 2A core spray system in-operable.
PROBLEM AND. INVESTIGATION....
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At 1130 hours0.0131 days <br />0.314 hours <br />0.00187 weeks <br />4.29965e-4 months <br /> on March 29, 1972, Unit 113 was at 800 MWe with the mode switch in "Run" and Unit :in was in "Refuel" with all rods in and no fuel moves in progress.
An electrical maintenance crew was overhauling the Transformer 28 high-side breaker at bus 23-1.
Bus 28 was being supplied from bus 29 via the 28-29 bus tie breaker.
(See figure 1)
The breaker auxiliary contacts in the breaker cubicle were exer-cised as part of the overhaul job.
When these contacts were moved to a position corresponding to that of a closed breaker, an interlock circuit was satisfied that automatically tripped the 28-29 bus tie breaker at bus'29.
This interlock circuit is designed to prevent tying bus 28 and 29 together when they are being fed from their parent 4160V buses.
When the bus tie breaker opened, power was lost to the motor con-trol centers supplying "A" standby gas treatment system, "2A" standby liquid pump, and the "2A" core spray system valves, which rendered these systems inoperable.
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- Dr. Peter April 25, 1972
- CORRECTIVE ACTION The riB" standby gas treatment system was started immediately by the operator and verified to be operable.
Normal electrical feed to bus 28 and its components was restored by 1330 hours0.0154 days <br />0.369 hours <br />0.0022 weeks <br />5.06065e-4 months <br /> the same day.
Maintenance procedural changes have been made to preclude a recurrence of this type of incident.
In addition, caution signs have been placed in the Transformer 28 and 29 high-side breaker cubicles and in the corresponding breaker cubicles on Unit 3.
WPW:do Sincerely, W. P. Worden Superintendent
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