ML20147A337

Final ASP Analysis - ANO 2 (LER 313-80-042)

ML20147A337
Person / Time
Site:	05000386
Issue date:	07/07/1980
From:	Christopher Hunter NRC/RES/DRA/PRB
To:
Littlejohn J (301) 415-0428
References
LER 1980-042-00
Download: ML20147A337 (4)

Text

PRECURSOR DESCRIPTION AND DATA NSIC Accession Number:

159136 Date:

July 7, 1980

Title:

Loss of Offsite Power at Arkansas Nuclear 2 The failure sequence was:

1. With the unit at 91% power, switchyard circuit breakers tripped ap-parently due to a ground fault, isolating the Mabelvale 500 kV line.

Unit 2 and Unit I generation 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 end due to feeder overload.

(The Mabelvale line became available but failed to close onto the ring bus because of a lack of synchonization.)

3.

Unit 2 tripped on DNBR due to decreasing RCP pump speed, a result of frequency and voltage upsets on the grid.

4.

The Morrilton East 161 kV line tripped on overload, leaving only Unit 1 generator output feeding the autotransformer and the Russellville East line carrying Unit I power generation.

Startup transformer No.

3 remained energized from the autotransformer, and startup transformer No.

2 remain tied to the 161 kV bus.

5.

The unit auxiliaries were transferred to startup transformer No.

3.

(The 6.9 kV buses had been transferred to startup transformer No.

3 prior to the start of the event.)

6.

Undervoltage relays on the 6.9 kV buses operated and shed the RC pumps and circulating water pumps.

7.

The 4.16 kV auxiliary circuit indicated low voltage and stripped the 4.16 kV buses from the startup transformer.

8.

Subsequently the auto transformer bank locked out due to a faulted relay, locking out startup transformer No.

3 and the Unit I startup transformer No.

1.

9.

This resulted in a loss of all auxiliary bus voltage.

10.

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:

Buses 2 Al and 2 HI were manually energized from startup transformer No.

2 four minutes later.

Approximately 55 minutes later all house loads were transferred to startup transformer No.

3 and both emergency diesels were secured.

Design purpose of failed system or component:

Offsite power provides the preferred source of power to safety related loads when the unit generator is unavailable.

Reactor at 90%

Loss of second Reactor trip Loss of Unit auxiliaries Loss of major Faulted Diesel power and loss 500-kV line due in DNBR due 161-kW transferred to 6.9-kV loads relay generators of 500-kV line to overload to decreasing line due SU transformer and 4.16-kV results in start and due to ground RC pump speed to over-

1. 3 bus loads due SU transformer provide fault. (One because of load to under-

1. 3 and Unit 1 power to 500-kv line voltage/fre-voltage SU transformer safety-previously quency problems

1. i lockout related out of (loss of volt loads service) age in all auxiliary buses)

Potential Severe Core Damage No No - turbine driven AFW train can pro-vide core cooling No No No No NSIC 159136 - Actual Occurrence for Loss of Offsite Power at Arkansas Nuclear 2

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 1

3 Yes Yes No No 4

5 6

7 8

9 Yes Yes No Yes 10 11 12 13 No Yes NSIC 159136 -

Sequence of Interest for Loss of Offsite Power at Arkansas Nuclear 2

CATEGORIZATION OF ACCIDENT SEQUENCE PRECURSORS NSIC ACCESSION NUMBER:

159136 LER NO.:

80-042 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 2 DOCKET NUMBER:

50-386 REACTOR TYPE:

PWR DESIGN ELECTRICAL RATING:

912 MWe REACTOR AGE:

1.6 years VENDOR:

Combustion Engineering ARCHITECT-ENGINEERS:

Bechtel OPERATORS:

Arkansas Power and Light LOCATION:

6 miles NW of Russellville, Arkansas DURATION:

N/A PLANT OPERATING CONDITION:

91% power TYPE OF FAILURE:

Made inoperable DISCOVERY METHOD:

Operational event COMMENT:

See NSIC 159134 (Arkansas Nuclear 1, 50-313, LER-80-022, July 7,

1980).