ML20147A481
| ML20147A481 | |
| Person / Time | |
|---|---|
| Site: | Callaway  |
| Issue date: | 05/26/2020 |
| From: | Christopher Hunter Office of Nuclear Regulatory Research |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1989-008-00 | |
| Download: ML20147A481 (5) | |
Text
B-409 ACCIDENT SEQUENCE PRECURSOR PROGRAM EVENT ANALYSIS LER No:
Event
Description:
Date of Event:
Plant:
483/89-008 Reactor trip, one EDG out of service, and loss of ESF bus June 23, 1989 Callaway 1 Summary A reactor shutdown was initiated from 100% power when a control rod bank failed to move and was declared inoperable at Callaway. When the turbine was tripped at 3%
power, a relay in the generator protective circuitry incorrectly stripped all power from a 4.16-ky engineered safety features (ESF) bus. The emergency diesel generator (EDG) that supplied backup power to the bus was out of service for maintenance, and the bus was without power for approximately 1 h and 43 min. The loss of power to the bus initiated the auxiliary feedwater (AFW) system turbine-driven pump, which supplied water to the steam generators. The conditional core damage probability estimated for this event is 1.2 x 10-6. The relative significance of this event compared with other postulated events at Callaway is shown below.
-LER 483/89-008 IE-7 1E-6 IE-5 IE-4 IE-3 IE-2 Trip1 LODFW-1 J L
Lk6OhP MTR AFW L.precursor cutoff 360 h AFW Event Description On June 23, 1989, Callaway was operating at 100% of rated power when control rod bank "B" failed to move during a monthly plant Technical Specifications surveillance.
The operators began an orderly shutdown of the plant in accordance with Tech Specs.
At 3% power the main turbine was tripped off. However, a generator output breaker protective relay incorrectly sensed that a flashover had occurred and cleared bus "B" in the 345-ky switchyard; this, in turn, cleared N'BO1, an ESF 4.16-ky bus supplied from
B-410 the switchyard. Usually, NBOl receives power from "A" EDG when normal power is lost; however, in this instance the "A" EDG was out of service for maintenance, so when the relay cleared the switchyard, a loss of power occurred on the bus. The loss of power to the ESF bus automatically initiated the turbine-driven AFW pump. Normal power to bus NBO1 was restored -'1.7 h after the trip.
Additional Event-Related Information Callaway's safety-related onsite power system is normally supplied from offsite sources through two independent supply paths:
" one preferred circuit from the switchyard to the startup transformer, which feeds 13.8-ky buses PA01 and PAO2, and 13.8-kV/4.16-kV ESF transformer XNBO2 (this circuit can be powered from the main generator via the unit auxiliary transformer).
" the second preferred circuit, which feeds 13.8-kV/4.16-kV ESF tranformer XNBO1 (this bus is powered from the switchyard).
ASP Modeling Assumptions and Approach This event has been modeled as a reactor trip with one of the two ESF buses unavailable.
Analysis Results The conditional probability of severe core damage for this event is 1.2 x 10-6. The dominant sequences associated with the event involve failure of secondary-side cooling and failure of feed and bleed. The dominant sequence for the event is highlighted on the following event tree.
B-411 TRAS[
T F
1 MF ORV/
PORV/
HI j I oEN E
TT OK OK 1D 12 C
OK OK OK 13 C0 14 CD OK OK 15 00 (1) 16 00 17 00 18 ATWS (1) OK for Class D Dominant core damage sequence for LER 483/89-008
B-412 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 483/89-008 Event
Description:
Reactor trip with unavailable ESF bus Event Date:
06/23/89 Plant:
Callaway 1 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator
- 1. OE+00 Probability CD TRANS Total ATWS 1.2E-06 1.2E-06 3.4E-05 3.4E-05 TRANS Total SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence 17 trans -rt AFW mfw HPI(F/B) 16 trans -rt AFW mfw -NPI(F/B)
NPR/-NPI 15 trans -rt AFW mfw -NPI(F/B) -NPR/-NPI porv.open 11 trans -rt. -AFW porv.or.srv.chall porv.or.srv.reseat -NPI NPR/
-NP I 12 trans -rt -AFW porv.or.srv.chall porv.or.srv.reseat NPI 18 trans rt non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence 11 trans -rt -AFN porv.or.srv.chall porv.or.srv.reaeat -BIPI NPR/
-NP I 12 trans -rt -AFE porv.or.srv.chall porv.or.srv.reseat NPI 15 trans -rt AFW mfw -NPI(F/B) -NPR/-NPI porv.open 16 trans -rt AFW mfw -NPI(F/B)
NPR/-NPI 17 trans -rt AFN mfw HPI(FIB)
End State CD CD CO CD CD ATWS End State CO CD CO CD CO ATWS Prob 4. 3E-07
- 2. 5E-07 2.4 E-07
- 1. 4E-07
- 1. 1E-07 3.4E-05 N Rec**
1.5E-02
- 1. 8E-02
- 1. 8E-02 1.1E-02
- 9. 2E-03 1.2E-01 Prob N Rec**
1.4E-07 1.lE-02 1.1E-07 9.2E-03 2.4E-07 1.8E-02 2.5E-07 1.8E-02 4.3E-07 1.5E-02 3.4E-05 1.2E-01 18 trans rt non-recovery credit for edited case SEQUENCE MODEL:
c:\\aap\\1989\\pwrbseal.cmp BRANCN MODEL:
c:\\asp\\1989\\callwy.sll PROBABILITY FILE:
c:\\asp\\1989\\pwr~bsll.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System trans 3.SE-04 loop 1.6E-05 loca 2.4E-06 Non-Recov
- 1. 00+00
- 5. 3E-01
- 4. 3E-01 Opr Fail Event Identifier: 483/89-008
B-413 rt rt/loop erserg. power AFW Branch Model:
l.OF.3+ser Train 1 Cond Prob:
Train 2 Cond Prob:
Train 3 Cond Prob:
Serial Component Prob:
afw/emerg.power mfw porv.or.srv.chall porv.or.srv. reseat porv.or. srv. reseat/emerg.power seal.loca.
ep.rec (si) ep. rec HPI Branch Model:
l.OF.2 Train 1 Cond Prob:
Train 2 Cond Prob:
HPI (F/B)
Branch Model:
l.OF.2+opr Train 1 Cond Prob:
Train 2 Cond Prob:
HPR/-HPI Branch Model:
l.OF.2+opr Train 1 Cond Prob:
Train 2 Cond Prob:
porv.open
- branch model file
- forced Minarick 06-14-1990 09:20:01 2.8E-04
- 0. 0E+00
- 2. 9E-03 3.8E-04 > l.3E-03 2.OE-02 l.OE-01 > Unavailable 5.0 E-02 2.8 E-04 5.0 E-02 1.0E+00
- 4. OE-02 3.OE-02 3.OE-02 2.7E-01 5.8E-01
- 2. 5E-02 1.OE-03 > l.OE-02 1.OE-02 1.OE-0l > Unavailable 1.OE-03 > 1.OE-02
- 1. OE-02 1.0E-01 > Unavailable 1.5E-04 > 1.OE-02 1.0 E-02 1.5E-02 > Unavailable l.0E-02 1.2E-01
- 1. OE400
- 8. OE-01
- 2. 6E-01 3.46-01
- 7. 06-02
- 1. 06+00
- 1. 1E-02
- 1. 06+00
- 1. 06+00
- 1. 06+00 1.06+00 8.46-01
- 8. 4-01
- 1. 06+00
- 1. 06+00 1.06-02 1.06-03 4.06-04 Event Identifier: 483/89-008