ML20149K466
| ML20149K466 | |
| Person / Time | |
|---|---|
| Site: | Mcguire |
| Issue date: | 05/28/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1987-016-00, LER 1987-017-00 | |
| Download: ML20149K466 (4) | |
Text
B-118 PRECURSOR DESCRIPTION SHEET LER No.:
370/87-016,
-017 Event
Description:
Trip with service water train and PORVs unavailable Date of Event:
9/6/87 Plant:
McGuire 2 EVENT DESCRIPTION Sequence On September 5, service water train 2A was taken out of service for cleaning after a test when it failed to provide adequate circulation to the train 2A component cooling heat exchanger, containment spray heat exchanger, and residual heat removal pump air-handling unit.
- Further, static invertor KXB was de-energized for periodic maintenance scheduled for September
- 7.
Alternate feed to bus KXB was provided via bus SMXT.
On September 6 at 1035, operations personnel started Compressor A
to verify operation after maintenance work on the unit.
Insulating tape on a connecting lug to a motor lead had worn through and allowed the lug to ground against the metal frame of the motor.
This short caused the 600-V motor feeder breaker and the 600-V feeder breaker for the 600-V motor control center SMXT to trip.
Trip of SMXT caused KXB to de-energize.
When KXB de-energized, it de-energized a relay sending a
signal to the turbine control system that the main turbine generator output breakers had de-energized.
This signal caused the main turbine
- throttle, governor, and intercept valves to close.
Loss of the turbine caused a pressure spike in the main steam and reactor coolant systems, and a high pressurizer pressure signal caused a reactor trip.
After trip, the pressurizer power-operated relief valves failed to open when the pressure exceeded the high-pressure set point.
This occurred since source power to the PORVs was lost with failure of KXB.
Loss of KXB also caused eight atmospheric dump valves and nine steam-dump-to-condenser valves to fail closed during the transient.
All steam generator PORVs opened and closed late.
One main steam line code safety valve failed to indicate that it had been opened, and another failed to open due to a
misadjusted pressure set point.
The 8-in.
moisture separator reheater valves failed to close both automatically and on reset (due to KXB),
which caused uncontrolled cooldown and a low reactor coolant Tavg signal that initiated main feedwater isolation.
Operators isolated main steam from second-stage reheater, shut down the main feed-water pumps, and controlled cooldown by manually starting AFW pumps A
and B.
The AFW pumps had to be manually started due to the loss of KXB (it is assumed that manual start was required upon main feed pump trip, but that auto-start was still available in low SC level).
After recovery from the
- trip, the unit was placed in hot standby (Mode 3).
The trip required that the solid state protection system train 2B be tested prior to returning the reactor to power.
This would render both service water trains inoperable from a. Technical Specifications stand-point.
Operations supervision permitted the test to be performed, understanding that the plant would be in hot standby at the time.
Event Identifier:
370/87-016,-017
B-119 Corrective Action Plant/Event Data Systems Involved:
Reactor pressure relief Secondary pressure control Component cooling water Containment spray system Residual heat removal system (low-pressure recirculation)
Service water system Components and Failure Modes Involved:
Pressurizer PORVs -
unavailable due to loss of bus KXB Moisture separator reheater valves -
open due to loss of bus KXB Main steam line code safety valve -
fails to open Eight atmospheric dump valves -
failed closed due to loss of bus KXB Nine steam dump to condenser valves -. failed closed due to loss of bus KXB Component Unavailability Duration:
N/A Plant Operating Mode:
1(100% power)
Discovery Method:
Operational event Reactor Age: 4.3 y Plant Type:
PWR Comments None.
MODELINC CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate Transient 1.0 No recovery assumed possible Branches Impacted and Branch Nonrecovery Estimate PORV.OPEN 1.0 No recovery assumed possible SS.DEPRESS 1.0 No recovery assumed possible HPI Base case One train unavailable Feed & Bleed Base case One train unavailable*
HPR Base case One train unavailable LPI Base case One train unavailable LPR Base case One train unavailable
- Failure of the PORVs to open faults feed and bleed.
Plant Models Utilized PWR plant Class B Event Identifier:
370/87-016,-017
B-120 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier:
370/87-016 Event
Description:
Trip with service water train and PORVs unavailable Event Date:
09/06/87 Plant:
McGuire 2 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator 1.OE+00 Probability CD CV TRANS Total TRANS Total 7.0E-06 7.0E-06
- 4. 3E-05
- 4. 3E-05
Sequence 121 trans -rt afw mfw -HPI(F/B)
-HPR/-HPI PORV.OPEN SS.DEPRESS 109 trans -rt
-afw -porv.or.srv.chall ss.releas.term HPI 101 trans -rt
-afw porv.or.srv.chall -porv.or.srv.reseat ss.releas
.term HPI 128 trans rt
- non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence 101 trans -rt
-afw porv.or.srv.chall -porv.or.srv.reseat ss.releas
.term HPI 109 trans -rt
-afw -porv.or.srv.chall ss.releas.term HPI 121 trans -rt afw mfw -HPI(F/B)
-HPR/-HPI PORV.OPEN SS.DEPRESS 128 trans rt
" non-recovery credit for edited case SEQUENCE MODEL:
c:\\asp\\newmodel\\pwrbnew.cmp BRANCH MODEL:
c:\\asp\\newmodel\\mcguire.new PROBABILITY FILE:
c:\\asp\\newmodel\\pwrbnew.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Re End State CD CV CV ATWS End State CV CV CD ATWS Prob 6.5E-06 4.1E-05 1.7E-06 N Rec**
8.8E-02
- 2. 9E-01 2.9E-01 3.4E-05 1.2E-01 Prob 1.7E-06 4.1E-05 6.5E-06 3.4E-05 N Rec**
- 2. 9E-01 2.9E-01
- 8. 8E-02 1.2E-01 Cov Opr Fail Event Identifier:
370/87-016
B-121 trans loop loca rt rt/loop emerg.power ep.rec afw afw/emerg.power mfw porv.or.srv.chall porv.or.srv.reseat porv.or.srv.reseat/emerg.power ss.releas.term HPI Branch Model:
l.OF.2 Train 1 Cond Prob:
Train 2 Cond Prob:
HPI (F/B)
Branch Model:
1.OF.2+opr Train 1 Cond Prob:
Train 2 Cond Prob:
HPR/-HPI Branch Model:
l.OF.2+opr Train I Cond Prob:
Train 2 Cond Prob:
PORV.OPEN Branch Model:
l.OF.l+opr Train 1 Cond Prob:
SS.DEPRESS Branch Model:
l.OF.1 Train 1 Cond Prob:
cond/mfw LPI/HPI Branch Model:
l.OF.2 Train I Cond Prob:
Train 2 Cond Prob:
lpr/-hpi.hpr LPR/HPI Branch Model:
l.OF.2 Train 1 Cond Prob:
Train 2 Cond Prob:
- 4. 8E-04 4.6E-06 2.4E-06 2.8E-04 O.OE+00 2.9E-03
- 1. OE+00
- 3. 8E-04 5.OE-02 2.OE-01 4.OE-02 3.OE-02 3.OE-02 1.5E-02 l.OE-03 l.OE-02
- 1. OE-01
- 1. OE-03
- 1. OE-02 1.OE-01 1.5E-04 1.OE-02 1.5E-02 1.OE-02
> 1.OE-02
" Unavailable
" l.OE-02
> Unavailable
> l.OE-02
> Unavailable
" l.OE+00 1.OE+00 3.9E-01 4.3E-01 1.2E-01 1.OE+00 8.OE-01 1.7E-01 2.6E-01 3.4E-01 3.4E-01 1.OE+00 1.1E-02 1.OE+00 3.4E-01 8.4E-01 S.4E-01 1.OE+00 1.OE+00 1.OE+00 3.4E-01 3.4E-01 1.OE+00 1.OE+00 1.OE-02 1.OE-03 4.OE-04 1.OE-02 > Unavailable 3.6E-02 > 1.OE+00 3.6E-02 > Unavailable 1.OE+00 1.SE-04 > 1.OE-02 1.OE-02 1.5E-02 > Unavailable 6.7E-01 1.5E-04 > l.OE-02 l.OE-02 1.5E-02 > Unavailable 1.OE-02 branch model file
- forced Minarick 05-16-1989 07:01:41 Event Identifier: 370/87-016