ML20147A502
| ML20147A502 | |
| Person / Time | |
|---|---|
| Site: | Columbia  |
| Issue date: | 05/26/2020 |
| From: | Christopher Hunter Office of Nuclear Regulatory Research |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1988-018-00 | |
| Download: ML20147A502 (5) | |
Text
B-286 Accident Sequence Precursor Program Event Analysis LER No:
397/88-018 Event
Description:
Both emergency diesel generators unavailable Date of Event:
May 22, 1988 Plant:
Washington Nuclear Plant, Unit 2 Sunmmary While at 0% power, an emergency diesel generator was discovered unavail-able while the other was out for maintenance.
Based on event specifics, this could have occurred at power.
The conditional probability of core damage has been calculated at 5.6 x 10-6.
The relative significance of this event compared with other potential events at WNPS 2 is shown below.
LER 397/88-018 IE-I E7IE-1:-5I-4 IE3IE-Trip L EP Unavail TripLOOP (360 hrs)
HPCI/RCIC Unavail (360 hrs)
Trip with HPCI Unavail Event Description While at 0% power, the control room operator noted that the green status light for the division two emergency diesel generator start circuit was not energized.
Investigation revealed that a two-position transfer switch was in a midposition between the " Normal" and "Emergency" posi-tion, which would probably prevent the diesel generator from starting on demand.
Since the switch was located at waist height and 6 in. from the edge of the control panel, it was postulated that the switch may have been inadvertently bumped into this middle position by an equipment operator.
Coincident with the unavailability of the division two emer-gency diesel generator, the division one diesel generator was out of service for modification.
Corrective action was taken to determine if protective barriers should be installed to prevent recurrence of this incident.
B-287 Event-Related Plant Design Information The emergency power system on WNPS 2 utilizes two diesel generators that supply power to two safety-related divisions.
A third diesel generator powers the high-pressure core spray pumps.
ASP Modeling Assumptions and Approach The event has been modeled as a 10-h emergency power system unavail-ability.
The likelihood of nonrecovery was estimated to be 0.34 (local recovery).
Analysis Results The conditional probability of core damage is estimated to be 5.6.
10-6.
The dominant core damage sequence (highlighted in the following event tree) is associated with a loss of offsite power occurring during the 10-h vulnerability (p =
8.6 x 0-5),
failure to recover emergency power (p =.34), and failure to recover electric power in the long term (p =0.17).
B3-288 LOOIUP H-C RV PCI RHER RHR EW GO P
RP (E
(R4FQ (SOC (OP OR 40 END COMA (105)
CHAL "Pps ADS MODE) MRCOE) OER NO STATE OK
- 4.
CORE DAMAE OK D, ORE DAMAE 4
GOREDMG OR OK OR 44 CORE DAMAE OR
- ,1 CORE DAMAGE GORED E
- 4.
CORE DAMAGE OK 49 GORE DAMAGE OK 4
G ORE DAMAGE OR OR S1 CORE DAMAGE OR OR 53 coRE DAMAGE 54 CORE DAMAGE OR S.
COGRE DAMAGE G4 OR DAMAGE OR OR MACOE DAMAGE o
COR DAMAGE OK MACOE DAMAGE OR OK
- 2 CORE DAMAGE 54 CORE DAMAGE OR 62 COe DAMAGE G3 ORE DAMAGE 0A CoRE DAMAGE OK 00 OR DAMAGE G0 ORE DAMAGE OK G9 ORE DAMAGE OK OK al CORe DAMAGE
.2 CORE DAMAE 93 COGRE DAMAGE 97 RAlWS Dominant Core Damage Sequence for LER 397/88-018
B-289 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier:
397/88-018 Event
Description:
Unavailability of emergency power Event Date:
05/22/88 Plant:
MNPSS 2 UNAVAILABILITY, DURATION=
10 NON-RECOVERABLE INITIATING EVENT PROBABILITIES LOOP SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator 8. SE-I5 Probability CD LOOP Total
- 5. SE-IS6 5.IOE-06 ATNS LOOP Total 5.EE-l7 5.6E-17 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence End State 83 loop EMERG.POWER -rx.shutdown/ep ep.rec CD 97 loop EMERG.POMER rx.shutdown ATWS 98 loop -EMERG.POWER rx.shutdown AIMS
-non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence End State 98 loop -EMERO.PONER rx.shutdown ATWS 83 loop EMERG.POWER -rx.shutdown/ep ep.rec CD 97 loop ENERG.POWER rx.shutdown AIMS 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\\sealmod\\bwrcseal.cmp BRANCH MODEL:
c:\\asp\\sealmod\\wnp2.sll PROBABILITY FILE:
c:\\asp\\sealmod\\bwr_csll.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch.
System Non-Rocov trans 4.SE-04 l.IE-t-I loop 1.6E-05 5.IE-01 loca 3.3E-06 5.IE-Il rx.shutdown 3.IE-05 l.IE+II rx.shutdown/ep 3.5E-04 l.IE+I0 pcs/trans 1.7E-01 l.IE+II srv.chall/trans.-scram l.IE+II l.IE+II Prob 5.IOE-06
- 8. 8E10l
- 8. 8E-10 Prob 8.8E-10
- 5. SE-IS
- 8. 8E-I0 N Rectk 1 BE-01 I 8 E-Il
- 3. 5E-01 N Rec**
- 3. 5E-Il 1.8E-Il
- 1. SE-Il which reflect the a reduction in risk Opt Fail Event Identifier: 397/88-018
B-290 srv.chall/loop.-scram srv.close EMERO.POWER Branch Model:
1.OF.2 Train 1 Cond Prob:
Train 2 Cond Prob:
ep. rec fw/pcs.trans fw/pcs.boca hpc i rcic o rd srv.ads lpos lpci (rhr)/lpon rhr (sdc) rhr (sdc) /-lpci rhr (sdo) Ilpci rhr(spcool) /rhr(sdc) rhr (spcooi) /-lpci.rhr (sdo) rhr(spoool) /lpci.rhr(sdc) rhrsw 1.06+00
- 5. 9E-02 2.9E-03 > 1.06-tOO 5.06-02 > Unavailable 5.76-02 > Unavailable 1.7E-01
- 4. 6E-01 1.06+00 2.0E-02 6.0OE-02
- 1. OE-02
- 3. 76-03 2.0E-02
- 6. OE-04 2.3E-02 2. OE-02
- 1. OE+00 2. OE-0 3 2.0E-03
- 9. 3E-02 2. OE-02 1.OE+00
- 1. 06.00 8.OE-01 > 3.4E-01
- 1. OE+/-00 3.4E-01 3.4E-01 3.4E-01 7.OE-01
- 1. OE+00 7.1E-01 3.4ZE-01 7.1lE-01 3.4E6-01 3.4E-01 1.06+00
- 3. 4E-01
- 3. 4E-01 1.06+/-00 3.4E-01
- 1. 0 -02 1.06-02 1.06-03 1.06-03 1.06E-0 3 2.06E-03
- branch model file
- forced Minarick 11-13-19899 13:31:53 Event Identifier: 397/88-018