ML20149K471
| ML20149K471 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 05/28/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1981-009-00 | |
| Download: ML20149K471 (4) | |
Text
Accession Number: 166384 e: May 22, 1981 LOOP at Monticello failure sequence was:
During a refueling outage an energized 4.16 kV breaker was racked out under load due to an operator error.
The resulting flashover created an electrical fault on No. 16 4.16 kV essential bus.
The No. 16 bus fault was picked up by the undervoltage relays on the IR transformer, which then tripped off before the overcurrent relays on bus No. 16 could trip off.
Sensing of the undervoltage condition on the IR transformer actuated automatic isolation of the entire 4.16 kV distribution system from the power source.
A momentary loss of all 4.16 kV busses occurred.
The No. lAR transformer and the No. 12 diesel generator closed into the faulted bus and subsequently tripped due to undervoltage and overcurrent, respectively.
The No. 11 diesel generator came on line and successfully supplied power to the No. 15 4.16 kV essential bus.
rective action:
Operator action restored the unfaulted 4.16 kV buses to service by returning transformer IR to service.
The faulted essential bus and damaged breaker were isolated.
Operator retraining program was revised to include proper breaker operations.
gn purpose of failed system or component:
Offsite power provides the preferred source of power to safety-ted loads when the unit generator is not operating.
is racked out fault on No. 16 trip prior to No. 16 generator close in No. 12 DC essential Core under load 4.16-kV bus bus overcurrent to faulted bus trip power to Damage relays, resulting in No. 15 bus loss of power to all 4.16-kV buses No No No No - plant in re-fueling shutdown No No No 166384 - Actual Occurrence for LOOP at Monticello
Operates No 1 Yes 2 No 3 Yes 4 (CD)
Yes 5 Yes 6 No 7 Yes 8 Yes 9 No 10 Yes 11 Yes 12 (CD)
Yes 13 Yes 14 NSIC 166384 - Sequence of Interest for LOOP at Monticello
NO.: 81-009 OF LER: May 22, 1981 OF EVENT: April 27, 1981 EM INVOLVED: Electrical system PONENT INVOLVED: 4.16 kV buses SE: Operator error initiating electrical fault UENCE OF INTEREST: LOOP AL OCCURRENCE: LOOP TOR NAME: Monticello KET NUMBER: 50-263 TOR TYPE: BWR GN ELECTRICAL RATING: 545 MWe TOR AGE: 10.4 years DOR: General Electric HITECT-ENGINEERS: Bechtel ATORS: Northern States Power Co.
ATION: 30 miles NW of Minneapolis, Minnesota ATION: N/A T OPERATING CONDITION: Refueling OF FAILURE: Inadequate performance; made inoperable OVERY METHOD: Operational event MENT: