ML20147A525
| ML20147A525 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 05/26/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1980-029-00 | |
| Download: ML20147A525 (5) | |
Text
IC Accession Number: 158860 te: April 30, 1980 e: Loss of Two Essential Buses and Loss of Decay Heat Removal Capability at Davis-Besse 1 failure sequence was:
. The reactor was in cold shutdown in preparation for refueling with the following equipment/system status:
- a. the head was detensioned but not removed (water level below the vessel flange)
- b. decay heat was being removed using decay heat pump No. 2
- c. decay heat pump No. 1 was out of service for maintenance with its associated piping drained
- d. the manway covers on the top of the steam generators had been removed.
The unit electrical lineup had been revised in preparation for work on buses "A" and "C". Buses E2 and F2 were supplied from breaker HBBF2. Essential distribution panels YI and Y3 were on their alternate feed (YBR) which is supplied by F2.
The ground fault relay on breaker HBBF2 actuated (possibly due to vibration caused by construction personnel in the switchgear room) and tripped the breaker.
This deenergized essential distribution panels Y1 and Y3,. which resulted in full SFAS actuation in levels 1 through 5.
The SFAS actuation isolated the RCS letdown line and caused the suction of decay heat removal pump No. 2 to transfer to the emergency sump. During the time the BWST outlet valves and emergency sump outlet valves were stroking, water gravity flowed into the emergency sump (approximately 1500 gallons). The decay heat pump was injecting BWST water into the RCS and increased RCS inventory approximately 3500 gallons. (The high pressure injection pumps and containment spray pump breakers had been racked out as required and hence did not actuate).
. The closing of the BWST outlet valve caused the decay heat pump to draw suction from the emergency sump which resulted in air being drawn into the pump suction. The pump was shut down to stop the injection and to prevent pump damage due to loss of suction.
The emergency sump valves were closed and power was removed from their operators. Decay heat removal loop No. 2 was refilled from the BWST, vented, and returned to service. The electrical lineup was restored with buses E2 and F2 separated.
Decay heat removal was unavailable for approximately 2-1/2 hours.
During that time interval, reactor coolant temperature increased from 90'F to 170'F.
The instrument ac system procedure was revised to allow inverters e supplied from the dc bus when the normal feed for the regulated tifiers from motor control centers E12A or F12A are to be ergized.
gn purpose of failed system or component:
The uninterruptable buses provide a continuous source of power to trol and instrumentation circuitry which cannot tolerate short term r interruptions.
its tribution panels of BSWT water Decay heat (DH Y1 and Y3 on into emergency loop #2 opera- alternate feed sump. Open refilled from F2 emergency sump from BWST, valves and vented, and closed BWST returned to valve result in service air being drawn into pump suction No Possible - time period to core damage is long. Train fl could possibly have been returned to service.
If not, throttled HPI pumps could possibly have been used for core cooling Possible - failure to trip pumps may have resulted in pump failure. If so, and if train #1 could not have been returned to service, then throttled HPI pumps could possibly have been used for core cooling. The time period to core damage is long and other mitigation paths could provide core cooling No No No 8860 - Actual Occurrence for Loss of Two Essential Busses and Loss of Decay Heat Removal Capability at Davis-Besse 1
al Lineup in Gravity Flow of Air in Resumed ed for Mainte- RWST Water into Pump
. Breaker Ground Emergency Sump. Suction Relay Actuates Open emergency sump o Vibration, Valves and Closed ing Breaker, BWST Valve Result lting in Level in Air Being Drawn FAS Actuation into DH Pump Suction _
No I No 2 3
No Yes 4 No Yes No No No Yes 10 No 11 Yes 12 NSIC 158860 - Sequence of Interest for Loss of Two Essential Buses and Loss of Decay Heat Removal Capability at Davis-Besse 1
C ACCESSION NUMBER: 158860 NO.: 80-029 E OF LER: April 30, 1980 E OF EVENT: April 19, 1980 TEM INVOLVED: Decay heat removal system, essential power system PONENT INVOLVED: Essential bus, decay heat pump SE: Tripped breaker resulted in loss of two essential buses and loss of decay heat removal UENCE OF INTEREST: Loss of two essential buses while in cold shutdown UAL OCCURRENCE: Loss of two essential buses and loss of decay heat removal capability CTOR NAME: Davis-Besse 1 KET NUMBER: 50-346 CTOR TYPE: PWR IGN ELECTRICAL RATING: 906 MWe CTOR AGE: 2.7 years DOR: Babcock & Wilcox CHITECT-ENGINEERS: Bechtel RATORS: Toledo Edison ATION: 21 miles east of Toledo, Ohio RATION: N/A NT OPERATING CONDITION: Cold shutdown E OF FAILURE: Made inoperable COVERY METHOD: Operational event MENT: