ML20147A549
| ML20147A549 | |
| Person / Time | |
|---|---|
| Site: | Duane Arnold  |
| Issue date: | 05/26/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1987-009-00 | |
| Download: ML20147A549 (4) | |
Text
3-80 PRECURSOR DESCRIPTION SHEET LER No.:
331/87-009 Event
Description:
Emergency power system unavailability due to incorrectly set overcurrent relays Date of Event:
5/27/87 Plant:
Duane Arnold EVENT DESCRIPTION Sequence During the performance of a simulated actuation test for a loss-of-coolant accident coincident with a loss of offsite
- power, the B emer-gency diesel generator tripped upon loading the core spray pump.
The generator tripped because of an incorrect set point on a newly installed phase differential overcurrent relay.
The relay was left at its most sensitive set point following construction acceptance testing.
The root cause of the generator trip was an inadequate construction acceptance procedure for the generator modification.
An inspection of the A diesel generator noted that its equivalent relay was also incorrectly set.
The A diesel generator had not yet been tested in the simulated actuation.
Corrective Action The construction acceptance procedure was modified such that the set points on both A and B EDG phase differential overcurrent relays were adjusted to design specifications.
- Further, electrical surge suppression circuitry was installed on the over current relays.
Plant/Event Data Systems Involved:
Emergency power Components and Failure Modes Involved:
Emergency diesel generator A -
incorrectly set phase differential overcurrent relay Emergency diesel generator B -
tripped on loading Component Unavailability Duration:
360 h (assumed)
Plant Operating Mode:
5(0% power, refueling)
Discovery Method:
Testing Reactor Age:
14.2 y Plant Type:
BWR Comments For analysis purposes, it has been assumed that this event could have occurred at power.
Event Identifier:
331/87-009
8-81 MODELING CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate Postulated LOOP Base case nonrecovery Branches Impacted and Branch Nonrecovery Estimate Emergency power
.1.0 Assumed not recoverable in the short term Plant Models Utilized BWR plant Class C Event Identifier:
331/87-009
B-82 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier:
331/87-009 Event
Description:
Emergency power unavailability due to incorrectly set relays Event Date:
05/27/88 Plant:
Duane Arnold UNAVAILABILITY, DURATION= 360 NON-RECOVERABLE INITIATING EVENT PROBABILITIES LOOP SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator 2.0E-03 Probability CD CV
( 1.1E-08 ATWS LOOP Total 6.7E-07 6.7E-07 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence 274 loop EMERG.POWER -scram ep.rec 841 loop EMERG.POWER scram
- non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
End State CD Prob N Rec**
3.3E-04 5.4E-02 6.BE-07 3.2E-01 ATWS Sequence End State 274 loop EMERG.POWER -scram ep.rec CD 841 loop EMERG.POWER scram ATWS
- non-recovery credit for edited case Note:
For unavailabilities, conditional probability values are differential values added risk due to failures associated with an event.
Parenthetical values indicate compared to a similar period without the existing failures.
SEQUENCE MODEL:
c:\\asp\\newmodel\\bwr_cnew.cmp BRANCH MODEL:
c:\\asp\\newmodel\\duarnold.new PROBABILITY FILE:
c:\\asp\\newmodel\\bwrcnew.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Prob 3.3E-04 6.8E-07 N Rec**
5.4E-02 3.2E-01 which reflect the a reduction in risk Opr Fall Branch trans loop System 8.6E-04 1.7E-05 Non-Recov 1.OE+O0 3.2E-01 Event Identifier:
331/87-009
B-83 loca scram slc.or.rods pcs/trans srv.chall/trans.-scram srv.chall/loop.-scram srv.close EMERG.POWER Branch Model:
1.OF.2 Train 1 Cond Prob:
Train 2 Cond Prob:
ep.rec fw/pcs.trans fw/pcs.loca hpci rcic crd srv.ads cond/fw.pcs lpcs lpci(rhr)/ipcs rhr(sdc) rhr(sdc)/-lpci rhr(sdc)/ipci rhr(spcool)/-ipci.rhr(sdc) rhr(spcool)/Ipci.rhr(sdc) c.i.and.v rhrsw rhrsw (c. i.and.v) 3.3E-06 3.5E-04 1.OE-02 1.7E-01 1.OE+00 1.0E+00 2.6E-02 2.9E-03 > 1.OE+00 5.OE-02 > Failed 5.7E-02 > Failed I.OE+O0 2.9E-01 4.OE-02 2.9E-02 6.OE-02 1.OE-02 3.7E-03 1.0E+O0 3.OE-03 1.OE-03 2.1E-02 2.OE-02 1.OE+00 2.OE-03 5.2E-01 1.OE-03 2.OE-02 5.OE-01 5.OE-01 1.OE+00 1.OE+O0 1.OE+00 1.OE+00 1.OE+00 I.OE+O0 8.0E-01 > 1.OE+00 1.7E-01 3.4E-01 3.4E-01 7.OE-01 7.OE-01 1.OE+00 7.1E-01 3.4E-01 3.4E-01 7.1E-01 3.4E-01 3.4E-01 1.OE+O0 1.OE+O0 1.OE+O0 1.OE+00 3.4E-01 3.4E-01 1.OE-02 1.OE-02 1.OE-02 1.OE-03 1.OE-03 1.OE-03 1.OE-03 1.OE-02 2.OE-03 branch model file forced Minarick 05-16-1989 07:00:26 Event Identifier:
331/87-009