05000346/LER-1980-029-03, /03L-0:on 800419,breaker HBBF2 on Bus B Opened, Allowing Two Buses to de-energize.Caused by Ground Fault Relay Actuated from Mechanical Vibration & Electrical Lineup for Maint.Decay Heat Pump Was Vented & Restarted

/03L-0:on 800419,breaker HBBF2 on Bus B Opened, Allowing Two Buses to de-energize.Caused by Ground Fault Relay Actuated from Mechanical Vibration & Electrical Lineup for Maint.Decay Heat Pump Was Vented & Restarted

ML19323A892
Person / Time
Site:	Davis Besse
Issue date:	04/30/1980
From:	Batch S TOLEDO EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML19323A891	List: 05000346/LER-1980-029, Forwards LER 80-029/03L-0 05000346/LER-1980-029-03, /03L-0:on 800419,breaker HBBF2 on Bus B Opened, Allowing Two Buses to de-energize.Caused by Ground Fault Relay Actuated from Mechanical Vibration & Electrical Lineup for Maint.Decay Heat Pump Was Vented & Restarted
References
LER-80-029-03L, LER-80-29-3L, NUDOCS 8005060178
Download: ML19323A892 (4)

LER-1980-029, /03L-0:on 800419,breaker HBBF2 on Bus B Opened, Allowing Two Buses to de-energize.Caused by Ground Fault Relay Actuated from Mechanical Vibration & Electrical Lineup for Maint.Decay Heat Pump Was Vented & Restarted

Event date:
Report date:
3461980029R03 - NRC Website

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8 60 61 DOCK 9T NUMBER 68 69 EVENT DATE 74 75 REPOR T D ATE 80 EVENT DESCRIPTION AND PROBABLE CONSEQUENCES Oio l o ( 21 l (NP-32-80-06) At 1400 hours0.0162 days <br />0.389 hours <br />0.00231 weeks <br />5.327e-4 months <br />, breaker TIBBF2 on "B" bus opened.

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The decay heat pump had to be shutdown to stop l

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Air in the piping delayed the pump restart.

Reactor coolant tempera-l lture rose above the 140 F specification for Mode 6.

No significant contamination and l o e l o l 7 l l no of f site releases resulted from the incident. Adequate core cooling existed at all l g jtimes.

Affected T.S. were 3.9.8, 3.9.2, 3.8.2.2, 3.3.2.1, and 3.3.3.8.

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TOLEDO EDISON COMPANY DAVIS-BESSE NUCLEAR POWER STATION UNIT ONE SUPPLEMENTAL INFORMATION FOR LER NP-32-80-06 DATE OF EVENT: April 19, 1980 FACILITY: Davis-Besse Unit 1 IDENTIFICATION OF OCCURRENCE:

Inadvertent Safety Features Actuation System (SFAS)

Actuation From Loss of Two Essential Distribution Panels Conditions Prior to Occurrence: The unit was in Mode 6, with Power (MWT) = 0, and Load (Gross MWE) = 0.

The reactor head was detensioned.

Reactor water level was approximately 65 inches above the centerline of the hot leg outlet (approximately 19 inches below reactor flange).

Description of Occurrence: At approximately 1400 hours0.0162 days <br />0.389 hours <br />0.00231 weeks <br />5.327e-4 months <br /> on April 19, 1980, the ground fault relay on breaker HBBF2 on "B" bus actuated possibly due to a mechanical vibra-tion from constructioh personnel working in the switchgear room. The unit electrical lineup at this time deviated from the normal power operation lineup in preparation for the work to be performed on "C" and "A" buses during the unit outage.

Bus E2 and F2 were supplied from breaker HBBF2, and esaential instrumentation distribution panels Y1 and Y3 were on their alternate supply (YAR) from E2 (E23). YBU had automatically trans-ferred to its alternate feed (YBR) which is supplied by F2 (F23). Therefore when HBBF2 tripped from the ground fault relay actuation, two essential distribution panels were de-energized placing the unit in the action statement of Technical Specification 3.8.2.2.

The loss of power also caused the unit to enter the action statements of Technical Specification 3.9.2 for the loss of one source range nuclear instrument, Technical Specification 3.3.3.8 for the loss of remote indication of fire detection, and Technical Specification 3.3.2.1 for the loss of containment radiation monitoring.

The loss of Y1 and Y3 resulted (as designed) in a full SFAS actuation in levels 1 through 5.

Since the unit was in Mode 6, the high pressure injection pump motors and containment spray pump motors had their breakers racked out to assure the pumps did not actuate.

Decay Heat Pump #2 had been in service recirculating water through the reactor and Decay Heat Pump #1 was removed from service for maintenance. The SFAS actuation caused the suction of Decay Heat Pump #2 to be transferred to the emergency sump.

During the time the Borated Water Storage Tank (BWST) outlet valves and the emergency sump outlet valves were stroking,' water was gravity fed into the lower elevation emcegency sump from the BWST.

Decay Heat Pump #2 was injecting water from the BWST into the reactor which raised the water level in the Reactor Coolant System (RCS). Approximately 3,500 gallons were injected into the RCS of which a small amount flowed out several lengths of tygon tubing being used for positive RCS level indication. Approximately 1,500 gallons were transferred into the emergency sump during the valve stroking which eventually drained to the normal sump area, The nor-i mal sump discharge was isolated by the SFAS actuation and the water was contained within the area of the sump.

The SFAS actuation automatically transferred the running Decay Heat Pump #2 suction to the emergency sump which caused an interlock to isolate the pump from the RCS let-down line. The closing of the BWST outlet valve caused the pump to draw a suction from LER #80-029

TOLEDO EDISON COMPN 1Y DAVIS-BESSE NUCLEAR POWER STATION UNIT ONE PAGE 2 SUPPLEMENTAL INFORMATION FOR LER NP-32-80-06 the emergency sump which resulted in air being drawn into the Decay Heat Pump #2 suction. At 1402 hours0.0162 days <br />0.389 hours <br />0.00232 weeks <br />5.33461e-4 months <br />, Decay Heat Pump #2 was shutdown to stop the injection, placing the unit in the action statement of Technical Specification 3.9.8.

At the time of the incident, there were 44 persons in containment.

All unnecessary personnel were notified to leave containment and the auxiliary building due to the stutdown of the normal ventilation system from the power loss.

With the decay heat pump de-energized while attempting to refill the Decay Heat #2 loop from the BWST, the reactor coolant temperature increased above the 1400F limita-tion for Mode 6.

Due to the efforts to recover from the loss of power, the fire watch required by the action statement of Technical Specification 3.3.3.8 was not in violation of Tech-completed within the required time interval, placing the unit nical Specification 3.3.3.8.

At approximately 1630 hours0.0189 days <br />0.453 hours <br />0.0027 weeks <br />6.20215e-4 months <br />, decay heat flow was re-established at a maximum reactor coolant temperature of approximately 170 F.

At the fire watch was completed, removing the unit from violation of Tech-1700 hours, nical Specification 3.3.3.8.

The electrical lineups were restored with Bus E2 and F2 separated. After a megger check on F2 the individual motor control centers were restored one at a time. The recovery was completed at approximately 2100 hours0.0243 days <br />0.583 hours <br />0.00347 weeks <br />7.9905e-4 months <br /> on April 19, 1980.

Designation of Apparent Cause of Occurrence: The root cause of this occurrence was the tripping of HBBF2 (probably due to a mechanical shock from construction personnal working in the area) during an electrical lineup which deviated from the normal power operation lineup when the unit was in Mode 6.

The electrical lineup was arranged to allow planned maintenance on "A" bus and "C" bus'.

The cause of the automatic trans-fer of YBU to YBR is still under investigation.

Analysis of Occurrence: There was no danger to the health and safety of the public or to station personnel.

No significant contamination and no offsite releases re-sulted from the incident. The core remained covered with water throughout the inci-dent and adequate core cooling existed.

Corrective Action

After the emergency sump valves were closed, power was removed from the motor operators to prevent their inadvertent opening.

Power will be removed from these valves in the future when the unit is in Modes 5 or 6.

Procedures which have been modified to assure this is completed include:

Modification No.

Procedure Title T-4568 Decay Heat and Low Pressure Injection Operations Procedure, SP 1104.04 T-4569 Emergency Core Cooling System Subsystems Monthly Test, ST 5051.01 LER #80-029 l

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o TOLEDO EDISON CGMPANY DAVIS-BESSE NUCLEAR POWER STATION UNIT ONE PAGE 3 SUPPLEMENTAL INFORMATION FOR LER NP-32-80-06 Modification No.

Procedure Title T-4570 Pre-Startup Checklist, PP 1102.01 T-4571 Plant Startup Procedure, PP 1102.02' T-4572 Plant Shutdoni and Cooldown, PP 1102.10 Also a modification (T-4558) was made to the Instrument AC System Procedure SP 1107.09, to allow the inverters to be supplied from the DC Bus when the normal feed for the regulated rectifiers from motor control centers E12A or F12A are to be de-energized.

Warning signs will be placed in the high voltage switchgear rooms to warn personnel in the area the cabinets are sensitive to mechanical vibrations.

Failure Data: There has been one previous reported occurrence of the inadvertent transfer of water to the emergency sump. The cause of the earlier occurrence was a component failure within the SFAS, see Licensee Event Report NP-33-79-06 (79-005).

LER #80-029 O

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