ML20147A332
| ML20147A332 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 07/07/1980 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1980-022-00 | |
| Download: ML20147A332 (4) | |
Text
PRECURSOR DESCRIPTION AND DATA NSIC Accession Number:
159134 Date:
July 7, 1980
Title:
Loss of Offsite Power at Arkansas Nuclear I The failure sequence was:
- 1. With the unit at 100% power, switchyard circuit breakers tripped apparently due to a ground fault, isolating the Mabelvale 500 kV line.
Unit 2 and Unit 1 generation was transferred to the Fort Smith 500 kV line.
(The Mayflower line was out of service.)
- 2.
The Fort Smith 500 kV line tripped open at the Fort Smith and due to feeder overload.
(The Mabelvale line became available but failed to close onto the ring bus because of a lack of synchonization.)
- 3.
The Morrilton East 161 kV line tripped on overload, leaving only Unit I generator output feeding the auto transformer and the Russellville East line carrying Unit 1 power generation.
Startup transformer No.
1 remained energized from the autotransformer and startup transformer No.
2 remained tied to the 161 kV bus.
- 4.
A manual runback was initiated following an automatic generator runback.
The reactor subsequently tripped.
- 5.
Auxiliary loads were transferred to startup transformer No.
1, which was already experiencing low output voltage.
- 6.
The autotransformer bank locked out due to a faulted relay, locking out startup transformer No.
1 and Unit 2 startup transformer No.
3.
- 7.
This resulted in a loss of all auxiliary bus voltage.
- 8.
The unit diesel generators started and provided power to safety-related loads.
(Power remained available by manual transfer from startup transformer No.
2.)
Corrective action:
Approximately 65 minutes later house loads were transferred to startup transformer No.
1.
Design purpose of failed system or component:
Offsite power provides the preferred source of power to safety re-lated loads when the unit generator is unavailable.
Reactor at 100%
Loss of second Loss of 161-kV Manual reactor Auxiliary loads Faulted relay Diesel power and loss 500-kV line line due to runback and sub-transferred to results in generators of 500-kV line due to overload overload sequent reactor startup trans-SU trans-start and due to ground trip former #I former #1 provide fault (one (which was lockout (loss power to 500-kV pre-already experi-of voltage on safety-viously out encing low all auxiliary related of service) output voltage) buses) loads Potential Severe Core Damage No No - turbine-driven AFW train available for core cooling No No No NSIC 159134 - Actual Occurrence for Loss of Offsite Power at Arkansas Nuclear I
Loss of Turbine Emer-Auxiliary PORV PORV or High Long Potential Sequence Offsite Generator gency Feedwater and Demanded PORV Isola-Pressure Term Severe No.
Power Runs Back Power Secondary tion Valve Injection Core Core and Assumes Heat Removal Closure Cooling Damage House Loads No 1
No 2
No 3
Yes 4
Yes 5.
No 6
(F)
No 7
Yes 8
Yes 9
No 10 Yes II No 12 Yes 13 NSIC 159134 -
Sequence of Interest for Loss of Offsite Power at Arkansas Nuclear - Unit 1
CATEGORIZATION OF ACCIDENT SEQUENCE PRECURSORS NSIC ACCESSION NUMBER:
159134 LER NO.:
80-022 DATE OF LER:
July 7, 1980 DATE OF EVENT:
June 24, 1980 SYSTEM INVOLVED:
Offsite power COMPONENT INVOLVED:
Transmission lines, relay CAUSE:
Sequential loss of transmission lines due to ground fault and
- overload, transformer lockout due to unspecified relay fault.
SEQUENCE OF INTEREST:
Loss of offsite power ACTUAL OCCURRENCE:
Loss of offsite power REACTOR NAME:
Arkansas.Nuclear 1 DOCKET NUMBER:
50-313 REACTOR TYPE:
PWR DESIGN ELECTRICAL RATING:
850 MWe REACTOR AGE:
5.9 years VENDOR:
Babcock & Wilcox ARCHITECT-ENGINEERS:
Bechtel OPERATORS:
Arkansas Power and Light LOCATION:
6 miles NW of Russellvile, Arkansas DURATION:
N/A PLANT OPERATING CONDITION:
100% power TYPE OF FAILURE:
Made inoperable DISCOVERY METHOD:
Operational event COMMENT:
See NSIC 159136 (Arkansas Nuclear 2, 50-368, LER 80-042, July 7,
1980).