ML19309A167
| ML19309A167 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 11/21/1977 |
| From: | Mattimoe J SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| To: | Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| Shared Package | |
| ML19309A168 | List: |
| References | |
| NUDOCS 8003260879 | |
| Download: ML19309A167 (2) | |
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SACRAMENTO MUNICIPAL UTIUTY DISTRICT C 6201 S Street. Box 15830. Sacnmento California 95813: (916) 452-3211 November 21, 1977
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rE Director of Regulatory Operations
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ATTN:
Mr. R. H. Engelken "g b M NRC Operations Office, Region V l
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1990 North California Boulevard Walnut Creek Plaza, Suite 202 1A ang
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Walnut Creek, California 94596 N
Re: Operating License DPR-54 2
Docket No. 50-312 Reportable Occurrence 77-14 K
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Deat Mr. Engelken:
In accordance with Technical Specifications for Rancho Seco Nuclear Generating Station, Section 6.9.l'and Regulatory Guide 1.16, Revision 4, to Municipal Utility District is hereby reporting Section C.2.b.1, @the_ Sacr the following as 0-77-147 2
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on October 19, 1977, while performing a refueling outage preventive maintenance check of the reactor coolant pump undervoltage and phase balance relays, it was discovered that two of the phase balance relays for Reactor Coolant Pump C had failed nonconservatively. The undervoltage and phase balance relays comprise the pump monitor portion of the reactor protection system. TH,5 pump monitors serve to reduce the ruclear overpower trip setpoint to 55 percent:
of full power when only one RCP in each coolant loop is operating and to trip the reactor upon loss of two RCP's in one loop or upon loss of one or both RCP's during two ptanp operation.
The undervoltage relays are the primary indicators for a reactor coolant pump not operating. If the pump has been shut.down or if power is lost to the pump, the four undervoltage relay contacts for that pump will open, sending a signal to each RPS channel. The phase balance relays act as a backup to the undervoltage relays to handle those instances where a fault occurs in one or more of the three phases of the RCP motor power supply _ but the breaker
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fails to open. If this were to occur, the undervoltage relay may still indicate J
proper pump operation when in fact that is not the case. The phase balance
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relays will detect the fault by comparing the individual phases and send a signal to the four RPS channels.
The failure of these two relays meant that this backup pump monitor signal from one reactor coolant pump to two of the four RPS channels was not functioning. Signals to the two remaining D.PS channels, sufficient to trip
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the reactor, were still operable. To insure proper calibration of these pump j
p monitor relays, an electrical maintenance procedure will be developed for the l
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l Mr. R. H. Engelken Page 2 November 21, 1977-PM check. One of the defective relays was replaced, and the other was recalibrated, returning the system to operation. The relays found out of calibration are Model 21-172 phase balance relays manufactured by Wilmar Electronics, Inc.
.(serial numbers 009, 011).
i No plant transient or shutdown resulted from this occurrence.
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l Respectfully submitted, c
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- -- q J.'J. Mattimoe Assistant General Manager and Chief Engineer JJM:FTE: jim cs: Di =ctor, MIPC (3) g-Di.ector, IE (30) a)
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