ML19319B810

RO NP-33-77-68:on 770812,intermediate Range Nuclear Instrument NI-3 Indicated Constant Neutron Level.Caused by Min Voltage in Compensating Power Supply.Setpoint Reset & Indication Returned to Normal

ML19319B810
Person / Time
Site:	Davis Besse
Issue date:	09/15/1977
From:	George T, Lingenfelter J TOLEDO EDISON CO.
To:
Shared Package
ML19319B706	List: ML19319B703 ML19319B810
References
NUDOCS 8001270274
Download: ML19319B810 (2)

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! DAVIS-BESSE UNIT ONE NUCLEAR POWER STATION SUPPLEMENTAL INFORMATION FOR LER NP-33-77-68 1

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) DATE OF EVENT: August 12, 1977 1

FACILITY: Davis-Besse Unit 1 i IDENTIFICATION OF OCCURRENCE: Loss of Intermediate Range Nuclear Instrument NI-3

! Conditions Prior to Occurrence: The plant was in Mode 2,' with Power (MWT) = 0, and I Load (MWE) = 0.

Description of Occurrence: At 1910 hours0.0221 days <br />0.531 hours <br />0.00316 weeks <br />7.26755e-4 months <br /> on August 12, 1977 (about 14 hours1.62037e-4 days <br />0.00389 hours <br />2.314815e-5 weeks <br />5.327e-6 months <br /> after initial criticality), spurious in ?.ication was observed on Intermediate Range Nuclear j Instrument NI-3. Intermediate Range Nuclear Instrument NI-4 was indicating a con-j stant neutron level. This placed the unit into Action Statement 4 of Technical Specification 3.3.1.1 which requires both Intermediate Range Nuclear Instruments to be operable.

This occurrence was not discovered to be reportable until review of the unit logs on August 29, 1977.

I Designation of Aoparent Cause of Occurrence: It was discovered that the compensat-j ing power supply to the nuclear instrument was set at the minimum voltage instead

of 25 volts D.C. The instrument cannot operate properly with reduced voltage at the power supply. It is suspected that personnel error caused the voltage to be changed, but it is not known how it was changed.

i 4 Analvsis of Occurrence: There was no threat to the health and safety of the public or station personnel. Intermediate Range Nuclear Instrument NI-4 was operable during

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the period when NI-3 was inoperable.

Corrective Action: Immediately the setpoint was reset to 25 volts D.C. and the indi-1 cation returned to normal. To prevent recurrence, a revision is being made to the Reactor Protection System Monthly Test, ST 5030.02, to include a check on these power supplies.

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] Failure Data: No previous losses of Intermediate Range Nuclear Instruments have 1 occurred.

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