ML20156A215
| ML20156A215 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 06/04/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1980-038-01 | |
| Download: ML20156A215 (4) | |
Text
PRECURSOR DESCRIPTION AND DATA NSIC Accession Number: 164453 Date:
February 2, 1981
Title:
Brief Loss of Offsite Power and Degraded Load Shed Capability at San Onofre 1 The failure sequence was:
- 1. With the reactor in cold shutdown, an operator intended to transfer kV buses I-C and 2-C from auxiliary transformer C to auxiliary transformers A and B.
- 2.
The operator opened the bus tie breaker by mistake instead of the auxiliary transformer C bus supply breakers.
- 3.
Buses 1-C and 2-C de-energized as auxiliary transformer C de-ener-gized, de-energizing CVCS,
- 4.
Both diesel generators started and were available for loading.
- 5.
Bus IC source breaker 11C02 did not open to shed loads on bus IC because dc bus control power to the undervoltage logic scheme was deenergized due to a mispositioned switch.
Corrective action:
Power was restored by reenergizing auxiliary transformer C within seconds.
The station was to implement administrative controls on safety-related dc control circuits prior to the end of the refueling outage.
Design purpose of failed system or component:
Offsite power provides the preferred source of power to safety-related loads when the unit generator is not available.
Load shedding is provided to strip safety-related buses of all large loads prior to initiation of the diesel loading sequence.
This prevents overloading of the diesel due to starting surges.
Reactor in Operator error Loss of Diesel generators Offsite shutdown and results in power to start and are power operator intends opening of bus buses 1-C available for restored to transfer 1-C tie breaker in and 2-C loading.
Bus 1C and 2-C buses lieu of trans-source breaker from auxiliary former C bus fails to. open due transformer C supply breakers to unavailable to auxiliary undervoltage transformers A scheme and B Potential Severe Core Damage No No No Possible -
if offsite power restora-tion delayed extensively No NSIC 164453 - Actual Occurrence for Brief Loss of Offsite and Degraded Load Shed Capability in San Onofre 1
Loss of Turbine Emer-Auxiliary PORV PORV or High Long
.Offsite Generator gency Feedwater and Demanded PORV Isola-Pressure Term Power Runs Back Power Secondary tion Valve Injection Core and Assumes Heat Removal Closure Cooling House Loads Potential Severe Core Damage Sequence No.
No No No I
2 3
Yes Yes 4
5 No No 6
Yes Yes 7
8 9
No Yes 10 11 12 13 No Yes NSIC 164453 - Sequence of Interest for Brief Loss of Offsite Power and Degraded Load Shed at San Onofre 1
CATEGORIZATION OF ACCIDENT SEQUENCE PRECURSORS NSIC ACCESSION NUMBER:
164453 LER NO.:
80-038 Rev.
I DATE OF LER:
February 2, 1981 DATE OF EVENT:
November 22, 1980 SYSTEM INVOLVED:
Offsite power COMPONENT INVOLVED:
4 kV bus circuit breakers CAUSE:
Operator error SEQUENCE OF INTEREST:
LOOP ACTUAL OCCURRENCE:
LOOP and degraded load shed capability REACTOR NAME:
San Onofre 1 DOCKET NUMBER:
50-206 REACTOR TYPE:
PWR DESIGN ELECTRICAL RATING:
436 MWe REACTOR AGE:
13.4 years VENDOR:
Westinghouse ARCHITECT-ENGINEERS:
Bechtel OPERATORS:
Southern California Edison LOCATION:
5 miles south of San Clemente, California DURATION:
N/A PLANT OPERATING CONDITION:
Cold shutdown TYPE OF FAILURE:
Failed to start DISCOVERY METHOD:
Operational event COMMENT:
The utility believes the dc control switch was mispositioned during the current refueling outage, although this cannot be confirmed.
See also NSIC No.
161910 (San Onofre, 50-206, LER 80-038, Dec.
9, 1980).