ML20149K358
| ML20149K358 | |
| Person / Time | |
|---|---|
| Site: | Hatch  |
| Issue date: | 05/28/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1988-018-00 | |
| Download: ML20149K358 (5) | |
Text
B-i125 Accident Sequence Precursor Program Event Analysis LER No:
Event
Description:
Date of Event:
Plant:
321/88-018 Reactor scram with loss of nonessential loads and RCIC degraded operation December 17, 1988 Hatch Unit 1 Summnary Following a reactor scram, a loss of power to the nonessential loads was experienced.
During the recovery from the scram, the RCIC system tur-bine tripped on the second and several later initiations of the system on overspeed but was successfully recovered.
The conditional core damage probability associated with the event is 1.5 x 10-5.
The rela-tive significance of this event compared with other potential transients at Hatch 1 is shown below.
1E-8 1 E-7 LER 321/88-018 1]E-6 1E-51E2 I E-4 1 E-3 I E-2 Trip I
HPCI/RCIC Unavail (360 hrs)
LO-OP LEP Unavail (360 hrs)
Trip with HPCI Unavail Event Description The reactor was at -85% power when the main turbine tripped on a loss of electrohydraulic control system (EHC) pressure, resulting in a reactor scram.
It is believed that the loss of EHO system pressure was caused by an operator racking out EHG breakers for the wrong unit.
Upon trans-fer of the nonessential loads to the startup auxiliary transformer (SAT)
(as expected) the protective relaying for SAT ID actuated (caused by a malfunctioning relay), resulting in a loss of power to the nonessential loads.
The emergency diesel generators started because of a temporary undervoltage condition on the essential bus but did not load because the voltage transient was over and normal voltage was being supplied.
B-126 Because of level transients caused by the reactor trip and subsequent loss of feedwater caused by the loss of power to the nonessential loads, RCIC was manually initiated to control reactor pressure vessel water level.
HPCI cycled off as designed; however, the ROIC turbine steam supply valve failed to close fully (a result of incorrectly tightened yoke bushing set screws), and upon reinitiation the RCIC turbine tripped on overspeed on several occasions.
The RCIC was restored and continued to assist in controlling reactor pressure.
Nonessential loads were not recovered until 22 h after the trip.
For the first 8 h, the battery-powered emergency lighting system func-tioned.
After this time period, lighting was unavailable except in the control room.
ASP Modeling Assumptions and Approach The event has been modeled as a LOFW with failure of RCIC.
The likeli-hood of not recovering RCIC was assumed to be 0.12.
Analysis Results The conditional probability of severe core damage estimated for this event is 1.5 x 10-5.
The dominant sequence postulated for this event (highlighted on the fol-lowing event tree) involves a failure of one of the SRVs to close (p= 0.036) with subsequent HPCJ (p =0.02) and ADS failure (p = 0.013, including operator error to initiate depressurization).
The highest probability sequence impacted by RCIC is a factor of 16 in probability below the dominant sequence, an indication of the lack of importance of RCIC failure in this event.
B-127 LET SUr C R
FGA I RDLG C
SOC G(X1JNG or I
MODE)
MODE)
OTviER SEO END No STATE OK CODE DANIAGE OK CODE DAMAGE CODE DAMAGE OK OK CODE DAMAGE OK CODE DAMAGE OK CODE DAMAGE OK CaAE DAMAGE OK CODE DAMAGE CODE DAMAG CORE DAMAGE OK CODE DAMAGE 0K OK Ox OK OCOD DAMAGE OK CODE DAMAGE OK OCHD DAMAGE OK CODE DAMAGE CODE DAMAGE CORE DAMAGE 00 OK CODE DAMAGE OK CODE DAMAGE OK OCOD DAMAGE OK C4DE DAMAGE OK CODE DAMAGE OK OCOD DAMAGE GCOD DAMAGE OK CODE DAMAGE CODE DAMAGE CODRE DAMAGE ATWS Domirranl Core Damage Sequence for LEA 321/88-018
B-128 CONDITIONAL CORE DANADE PROBABILITY CALCULATIONS Event Identifier:
321/88-018 Event
Description:
Trip with loss of non-essential loads and RCIC degraded Event Date:
12/17/88 Plant:
Harch I INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS SEQUENCE CONDITIONAL PROBABILITY SONS End State/Initiator I1.
SE-i-S Probability CD TRANS Total ATWS
- 1. SE-S5
- 1. 5E-O5
- 3. OE-O5 3.SOE-05 TRANS Total SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence 28 trans -rx.shotdown PCS/TRANS srv.chall/rrans.-scram srv.close EW/PCS.TRANS hpci srv.ads 12 trans -rx.shutdown PCS/TRANS srv.chall/trans.-scrars -srv.close FW/PCI.TRANS -hpci rhr(sdc) rhr(spcool)/rhr(sdc) 20 trans -rx.shutdown P05/TRANS srv.chall/trana.-scram -srv.close FW/PCS.TRANS hpci RCtC crd srv.ads 99 trans rx.shutdown
-- non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence 12 trans -rx.shutdown POS/TRANS srv.chall/Lrans.-scram -srv.close FW/PCS.TRANS -hpci rhr(sdc) rhr(spcool)/rhr(sdc) 20 trans -rx.shotdown P05/TRANS srv.chall/trans.-scram -srv.close FW/PCS.TRANS hpci ROTC crd srv.ads 28 trans -rx.shutdown POS/TRANS srv.chall/trans.-scram arv.ciose FW/PCS.TRANS hpci srv.ads End State CD CO CD P rob B. 3E-016
N Rec**
S. SE-0l
- 3. SE-SO N Rec*-
- 1. lE-01
-* non-recovery credit for edited case SEQUENCE MODEL:
a: \\sealmod\\bwrcseal.cmp BRANCH NODEL:
a:\\sealmod\\hatch.sll PROBABILITY PILE:
a:\\soalmod\\bwr-csll.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System trans 6.lE-54 loop 1.6E-05 loca 3.3E-06 Non -Recov
- 1. SE+SS 3.6GE-01 S.SE-Sl Opr Fail Event Identifier: 321/88-018
B-129 rx.shutdown rx.shutdown/ep P Cs!TRANS Branch Model:
l.OF.l Train 1 Cond Prob:
srv.chall/trans.-scrarn srv.chall/ioop.-scram srv.ciose emerg.power ep. rec FW/PCS.TRANS Branch Model:
1.OF.1 Train 1 Cond Prob:
fwlpcs. loca hpc i RCTC Branch Model:
1.0F.1 Train 1 Cond Prob:
o rd srv.ads ipo 5 lpci (rhr) /lpcs rhr (sdc) rhr (sdc)/-lpcl rhr (sdc) /lpci rhr~spcool) /rhr~sdc) rhr(spcoo~l) /-lpci.rhr(sdc) rhr(spcool) /lpci.rhr(sdc) rhrsw 3.0E-0 5
- 3. 5E-04 1.7E-01 > 1.00+00 1.7E-01 > Unavailable 1.00+00 1.00+00
- 3. 6E-02 5.4E0-04
- 1. 6E-01 4.6E-01 > 1.00+00 4.6E-01 > Unavailable
- 1. OE.00 2.9E-02 6.OE-02 > 1.00+00 6.00-02 > Failed 1.00-02
- 3. 7E-03
- 3. OE-03 1.00E-03 2.1E-02 2.0E-02 l.OE+00 2.00-03 2.OE-03 9'.3E-02 2.00-02 1.
E00+0 1.00+00 1.00+00 1.00+00 1.00+00 1.00+00 8.00-01 1.00+00 3.40-01 > 1.00+00
.3.
4E-01 7.00E-01 7.00-01 > 1.2E-01 1.00+00 7.10-01 3.40-01 7.10-01
- 3. 4E0-01
- 3. 4E0-01 1.00+00
- 3. 4E0-01
- 3. 4E0-01 1.00+00 3.4E-01 1.00-02 I.00-02 1.00-03 1.00-03 1.00-03 2.0E-03 branch model file
~*forced Minarick 11-14-1989 0 6:0 9 :15 Event Identifier: 321/88-018