ML20149K386
| ML20149K386 | |
| Person / Time | |
|---|---|
| Site: | Indian Point  |
| Issue date: | 05/28/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1986-035-00 | |
| Download: ML20149K386 (5) | |
Text
PRECURSOR DESCRIPTION SHEET LER No.:
247/86-035 Event
Description:
October 20, 1986 Plant:
Indian Point 2 EVENT DESCRIPTION Sequence At 0936 h the Unit 2 reactor tripped from 100% power when reactor trip breaker B unexpectedly opened because of loose wires in the relay racks.
Breakers RT3 and 4 were deenergized.
One of the reactor protec-tion relays had also been deenergized while a monthly SI surveillance test was being performed in a nearby equipment rack.
Following the trip, SG levels dropped rapidly as expected.
Both motor-driven auxiliary feed pumps started on low-low SG level.
While following the emergency recovery procedure, a control room operator discovered that auxiliary feed pump 21 had tripped when its breaker tripped for an unknown reason.
The pump was then successfully restarted from the control room.
AFW was used to maintain the SG water levels.
The steam-driven auxiliary-feed-pump steam relief valve had also popped open following the plant trip when its steam-pressure control valve opened because its set point was out of calibration on the low side.
The steam-pressure control valve received an automatic open signal on low-low steam generator level in two of the four SGs, ad-mitting steam up to the turbine governor valve.
The auxiliary-feed-pump speed changer setting was at minimum as designed, but response by the pressure control valve was too slow, which caused the relief valve to lift.
Corrective Action Repairs were made.
Plant/Event Data Systems Involved:
Two trains of AFW failed in operation Event Identifier:
247/86-035 D-1 1
Component Unavailability Duration:
NA Plant Operating Mode:.1 (100% power)
Discovery Method:
Operational event..
Reactor Age:
13.4 years Plant Type:
PWR Comments The FSAR states that upon SI actual signal, the MFW system will isolate.
An SI actual signal actuation is not reported to have occurred.
Upon RPS actuation, the MFW regulating valves should fully open, yet the LER states that the AFW pumps started as a result of low SG level and were used to maintain SG level.
Therefore, MFW is assumed to have tripped, even though the LER does not appear to say-'so..
The event was modeled assuming that the turbine-driven AFW pump was made unavailable when its steam side relief valve opened during pump start.
- This, in combination with the also unavailable motor-driven train produced the calculated core damage probability estimate.
It is possible that the turbine-driven AFW pump was available for steam generator cooling; if this was the case, the core damage probability estimate would be lower by a factor of -10.
- However, the LER does state that steam generator inventory was maintained by one of the motor-driven AFW pumps and does not clarify that the turbine-driven pump would have been available if required.
MODELING CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate Transient Base case nonrecovery Branches Impacted and Branch Nonrecovery Estimate AFW Base case Two of three trains failed on demand; one train was nonrecoverable MFW Base case Assumed failed in operation Plant Models Utilized PWR plant Class F Event Identifier:
247/86-035 D-12
CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS EventIdentifier:
247/86-035 Event
Description:
Trip, LOFW, and Two AFW Train Failures Event Date:
10/20/86 Plant:
Indian Point 2 INITIATIN6 EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator CV 1.OE+00 Probability TRANS Total
- 5.
IE-04
- 5.
IE-04 CD TRANS Total
CV Conditional Probability:
125 TRANS -RT AFW NFW HPIIF/B) -SS.DEPRESS -COND/MFW End State:
CD Conditional Probability:
126 TRANS -RT AFN MFW HPI(F/B) -SS.DEPRESS CDND/NFW End State:
ATWS Conditional Probability:
3.4E-05 3.4E-05 2.3E-04
- 1. 2E-04 3.4E-05 Event Identifier: 247/B6-035 D-13
J28 TRANS RT SEQUENCE CONDITIONAL PROBABILITIES Sequence End State Prob N Rec*f 119 TRANS -RT AFW MFW -HPItF/B) -HPR/-HPI PORV.OPEN -SS.DEPRESS
-COND/MFW 120 TRANS -RT AFW MFW
-HPI(FIB) -HPR/-HPI PORV.OPEN -SS.DEPRESS COND/MFW 122 TRANS -RT AFW MFW -HPI(F/B)
HPR/-HPI -SS.DEPRESS -COND/MFW 123 TRANS -RT AFW MFW
-HPI(F/B)
HPR/-HPI -SS.DEPRESS COND/MFW 124 TRANS -RT AFW MFW -HPI(F/B)
HPR/-HPI SS.DEPRESS 125 TRANS -RT AFW MFW HPI(F/B) -SS.DEPRESS -COND/MFW 126 TRANS -RT AFW MFW HPIIFIB) -SS.DEPRESS COND/MFW 127 TRANS -RT AFW MFN HPI(F/B)
SS.DEPRESS 128 TRANS RT CV CD 5.2E-05 5.8E-02 2.7E-05 3.OE-02 CV CD CD Cv CD CD ATWS
- 2.
- 1.
IE-04
- 1.
2E-:05 2.3E-04 *
- 1.
2E-04 *
- 1.
3E-05 3.4E-05
- 5.BE-02 3.OE-02
- 8.
8E-02 4.9E-02 2.5E-02 7.4E-02 1.2E-01
- dominant sequence for end state
- 4 non-recovery credit for edited case SEQUENCE MODEL:
ci\\asp\\newmodel\\pwrbtree.cmp BRANCH MODEL:
c: \\asp\\newmodel\\indpoint.txt PROBABILITY FILE:
c:\\asp\\newoodel\\pwrb.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System TRANS LOOP LOCA RT RT/LOOP EMERS,POWER AFW Branch Model:
1.OF.3+ser Train I Cond Prob:
Train 2 Cond Prob:
Train 3 Cond Prob:
Serial Component Prob:
AFW/EMERO.POWER Branch Model:
I.OF.I Train I Cond Prob:
MFW Branch Model:
I.OF.I Train 1 Cond Prob:
Event Identifier: 247/86-035
- 4. BE-04 4.6E-06 2.4E-06
- 2. BE-04 O.OE+00 2.9E-03 3.BE-04 > I.OE-O1 2.OE-02 > Failed i.OE-01 5.OE-02 > Failed 2,BE-04 5.OE-02 > I.OE+0O 5.OE-02 > Failed 2.OE-D1 > I.OE+O0 2.OE-Ol ) Failed Non-Recov I.OE+00 3.9E-01 4.3E-01 1.2E-01 I.OE+0O B.OE-Ol 2.6E-01 3.4E-01 3.4E-01 Opr Fail D-14
PORV.OR.SRV.CHALL PORV.OR.SRY.RESEAT PORV.OR.SRV.RESEAT/EMER6.POWER SS.RELEAS.TERM SS.RELEAS.TERM/-IFW HPI HP!(F/B)
HPR/-HPI PORY.OPEN SS.DEPRESS COND/MFW LPI/HPI LPR/-HPI.HPR LPRIHPI
- branch aodel file
- , forced Austin 09-11-1987 14:20:03
- 4.
OE-02
- 2.
OE-02 2.OE-02
- 1.
- 1.
- 1.
5E-03 M.E-03
- 1.
- 1.
OE-02
- 3.
- 1.
OE+00 M.E-04 W.E-0I L 5E-04
- 1.
OE+00
- 5.
OE-02 I.OE+00
- 3.
E-01
- 3.
E-01 B.
4E-0 I
- 8.
4E-01 I.OE+O0
- 1.
OE +00
- 1.
OE +00 M.E-01
- 3.
E-0l
- 1.
OE+00 I.DE400
- 4. 0E-02
- 4. 0E-02 Event Identifier; 247/86-035 D-15