ML20149K379
| ML20149K379 | |
| Person / Time | |
|---|---|
| Site: | Hatch  |
| Issue date: | 05/28/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1988-017-00 | |
| Download: ML20149K379 (5) | |
Text
8-262 Accident Sequence Precursor Program Event Analysis LER No:
366/88-017 Event
Description:
Reactor trip and failure of RCIC pump Date of Event:
May 27, 1988 Plant:
Hatch Unit 2 Summnary A deficient condensate and feedwater pump vent and fill procedure resulted in air binding in the condensate booster pumps, which caused a trip of main feedwater and subsequent reactor trip.
As the reactor level dropped in response to the reduced feedwater flow, HPCI and RCIG started as designed; however, RCIG failed to inject because of a failed limit switch.
The conditional probability of core damage has been esti-mated at 2.0 x 10-5.
The relative significance of this event compared with other potential events at Hatch 2 is shown below.
-LER 366/88-017 1 E-8 I E-7 I E-6 1E-5 1E-4 1E-3 1 E-2 Trip LOP EPUav" HPCI & RCIC(30hs Unavail (360 hrs)(30h)
Trip with HPCI Unavail Event Description While at 98%, operators were preparing a condensate pump for service later in the day.
In the process of filling and venting the pump, an air bubble was released into the condensate system, which tripped the condensate booster pumps and the reactor feedwater pumps.
Reactor level dropped, causing a reactor scram and automatic initiation of the HPCI and RCIC pumps.
Although RCIC started as designed, the pump failed to ramp up due to a failed limit switch on valve 2E51-F045.
As a conse-quence of the failed limit switch, the RCIC woodward controller would not respond to speed demands.
B-263 The root cause of the event has been identified as a deficient conden-sate and feedwater vent and fill procedure while the unit is at power.
Additionally, the limit switch on valve 2E51-F045 was replaced.
ASP Modeling Assumptions and Approach This event as been modeled as a loss of feedwater and reactor trip with RCIC failed.
Analysis Results The conditional probability estimated for the event is 2.0 x 10-5, a moderate significance event.
The dominant sequence to core damage (p =9.3 x 10-6) involves failure of an SRV to close following the trip (p =
0.036), failure of HPCI (p =
0.02), and failure to depressurize using ADS (p = 0.013).
The failure of RCIC impacts the third most domi-nant sequence (4.9 x 10-6).
In this sequence, all SRVs successfully close, but all high-pressure injection plus depressurization capability is lost.
The dominant core damage sequence is shown on the following event tree.
9
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SEG END IENT
&I CS 1M5 ISo COXJD o
MODE) MODE)OhE OK Ox CODE DAMAGE 08 OK 13 CCFE DAMAGE 08 0K OK OK
- 14.
GODE DAMAGE OK OK 0 CODE DAMAGE OK ROE DAMAGE OK G8 ORE DAMAGE 18 CCRE DAMAGE 20 GCRD DAMAGE OK 21 CORE DAMAGE OK OK Ox 23 CODE DAMAGE 24 CORE DAMAGE OK 25 C4DE DAMAGE En8 2
G ORE DAMAGE 28 GORE DAMAGE OK 28 GORE DAMAGE OK 08 30 CORE DAMAGE 32 CODE DAMAGE 33 COE DAMAGE 0K OK 3*
GORE DAMAGE 35 CORE DAMAE 38 CcDE DAMAGE
.31 CORE DAMAGE 38 GODE DAMAG go ATWS Dominant Core Damage Sequence for LER 366/88-017
13-265 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier:
366/88-017 Event
Description:
LOFW and RCIC fails to inject water Event Date:
05/27/88 Plant:
Hatch 2 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator
- 1. OE+00 Probability CD TRANS Total ATWS
- 2. SE-OS
- 2. OE-05 3.0OE-05
- 3. OE-05 TRANS Total SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence 28 trans -rx.shutdown PCS/TRANS srv.chall/trans.-scram srv.close FW/PCS.TRANS hpci srv.ads 12 trans -rx.shutdown PCS/TRANS srv.chall/trans.-soram -srv.close FW/PCS.TRANS -hpci rhr(sdc) rhr(spcool)/rhrisdc) 20 trans -rx.shutdown PCS/TRANS srv.chall/trans.-scram -srv.close FN/PCS.TRANS hpci RCIC crd srv.ads 99 trans rx.shutdown
-- non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence 12 trans -rx.shutdown PCS/TRANS srv.chall/trans.-scram -srv.close FW/PCS.TRANS -hpci rhr(sdc) rhr(spcool)/rhr(sdc) 20 trans -rx.shutdown PCS/TRANS srv.ohall/trans.-scram -srv.close FW/PCS.TRANS hpci RCIC crd srv.ads 28 trans -rx.shutdown PCS/TRANS srv.chall/trans.-scram srv.close FN/PCS.TRANS hoci srv.ads End State CD CD CD ATNS End State CO CD CD ATWS P rob
- 9. 3E-06
- 5. 2E-06 4.9E0 N Rec**
- 5. OE-01 1. 1E-5
- 5. OE-01 3.SE-55 l.0E+00
- Prob,
- 5. 2E-S6 4.9E-06
- 9. 3E-06
- 3. SE-OS N Rec**
1.11E-01 5.5OE-01
- 5. SE-S1 1.01+00 99 trans rx.shutdown non-recovery credit for edited case SEQUENCE MODEL:
c: \\asp\\sealmod\\bwrcseal.cmp BRANCH MODEL:
c:\\asp\\sealmod~hatch.sll PROBABILITY FILE:
c:\\asp\\sealmod\\bwr_csll.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System trans 6.11-54 loop 1.6E-05 loca 3.3E-056 Non-Recov 1.01+00
- 3. EE-01 5.OE-01 Opr Fail Event Identifier: 366/88-017
B-266 rx. shutdown rx.shutdown/ep PCSITRANS Branch Model:
1.0F.1 Train 1 Cond Prob; srv.chall/trans.-scram srv.chall/loop.-scram-srv.,os eme rg.power ep. rec FW/PCS.TRANS Branch Model:
1.6F.1 Train 1 Cond Prob:
fw/pcs.loca hpc i RCIC Branch Model:
l.OF.l Train 1 Cond Prob!
c rd s rv.ads 1 pca lpci (rhr) /lpcs rhr (sdc).
rhr(sdc)/-lpci rhr (sdc) /lpci rhr(spcool) /rhr(sdc) rhr (spcool) /-lpci. rhr (sdc) rhr(spcool) /lpci.rhr(sdc) rhrsw
- 3. 0OE-05
- 3. 5E-04 1.7E-01 > l.OE+00
>~7E0 Failed
- 1. 00+00 1.00+00 S.
6E-02 5.4 E-04 1.6E-01 4.6E-01 > 1.00+00 4.6k-01 > Failed
- 1. 00+00 2.9E-02 G.OE-02 > 1.00+00 6.00-02 > Failed 1.0 E-02 3.7E-03 3.0OE-03 1.00-03 2.1E-62 2.00-02 1.00+00 2.OE-03 2.00-03 9.3E-02 2.OE-02
- 1. 00+00 1.00+00 1.00+00 1.0s+00 1.00+00
- 1. 0 Z+ 0 8.00E-01
- 1. 00+00 3.4E-01 > 1.00+00 3.4E-01 7.00-01 7.00-01 > 1.00+00 1.00+00 7.1E-01 3.4E-01 7.10-01 3.4E-01 3.4E0-01 1.00+00
- 3. 4E-01
- 3. 4E0-01 1.0 0+00
- branch model file
- ~forced Minarick 11-13-1989 17 :24 :28 Event Identifier: 366/88-017