ML20135H299
| ML20135H299 | |
| Person / Time | |
|---|---|
| Site: | Oyster Creek |
| Issue date: | 05/14/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1990-005-00 | |
| Download: ML20135H299 (5) | |
Text
B-53 ACCIDENT SEQUENCE PRECURSOR PROGRAM EVENT ANALYSIS LER Number: 219190-005 Event
Description:
"B" ESF 480-V feeder and isolation condenser "A" failure Event Date: April 21, 1990 Plant: Oyster Creek Summary A ground fault in the feeder to 480-V bus 1B2 caused a loss of power to the bus and its loads, rendering a number of "B" train safety systems inoperable. The "B" 125-V battery chargers were deenergized, and the battery was forced to carry the "B" train DC loads. After about 11 h, battery voltage declined sufficiently that it was decided to initiate a manual scram. After the reactor was scrammed, "A" isolation condenser was found to be inoperable when a DC isolation valve failed. The conditional core damage probability estimated for this event is 8.8 x 10-5 The relative significance of this event compared to other postulated events at Oyster Creek is shown below.
IE-7 1E-6 1E-5 1E4 E-3 IE-2 precrso ~wf
~W~ L360 hEP Trip Event Description The plant was operating at 100% power when a ground fault in the feeder to 480-V bus 1B2 occurred. The bus supply breaker opened, deenergizing the bus and its loads.
These included motor control centers 1B2, 1B24, 1B23, 1B22, 1B21, lB21B, and 1B21A. Equipment affected included the drywell equipment drain tank pumps, "B" train battery chargers, containment spray system train 2, isolation condenser "B", "B" control rod drive pump, and standby gas treatment train "B". One booster pump in each train of core spray was also affected.
Loss of control of the drywell equipment drain tank pumps caused the drywell equipment
B-54 drain tank to overflow to the drywell floor drain sump, increasing "unidentified" leakage to the floor drain sump to greater than 5 gpm. This condition created a Limiting Condition for Operation (LCO) requiring that the plant be shut down within 12 h.
Loss of the battery chargers transferred the "B" train 125-V DC loads to the battery.
Batteries at Oyster Creek are rated for 1.5 h of operation under accident loading. Under the lighter demands of normal operations, the "B" battery carried its loads for 11 h before battery voltage dropped to a level that concerned plant operators. At that point, they initiated a manual scram.
Three hours later, the "A" isolation condenser was declared inoperable when one of its associated DC-powered valves experienced thermal binding and could not be operated.
Twelve hours after scram, the electrical fault on bus I1B2 was isolated, and the bus was repowered via a crosstie to bus 1A2. Shortly after that, the plant was placed in cold shutdown.
Additional Event-Related Information Many of the plant's major DC loads may be switched to feed from either "A" or "B" battery. However, the Oyster Creek Final Safety Analysis Report indicates that all chargers for the "A" and "B" batteries are fed through bus 1112. It therefore appears that only the "C" battery would be unaffected by the loss of bus 11B2.
Modeling Assumptions and Approach This event has been modeled as a reactor trip with unavailable isolation condenser (assumed operable locally, non-recovery likelihood = 0.34), unavailable reactor vessel (RV) makeup via the control rod drive (CRD) system, an unavailable containment spray train, degraded core spray, and degraded shutdown cooling. DC power was assumed available during trip mitigation.
Analysis Results The conditional probability of severe core damage estimated for this event is 8.8 x 10O5.
The dominant core damage sequence, highlighted on the following event tree, involves the observed trip with failure of high-pressure cooling and failure to depressurize using the automatic despressurization system (ADS).
B-55 MU 0C PRET SEQ END DOW CW OK OK OK OK 12 COREDAMAGE OK OK 12 OOREDAMAGE OK 14 CORE DAMAGE 15 CORE DAMAGE Ox 15 CORE DAMAGE I? CORE DAMAGE Ia CORE DAMAGE OK CK is CORE DAMAGE OK OK 20 COREDAMAGE OK 21 ORE DAMAGE OK L-t 22 COREDAMAGE OK 23 CORE DAMAGE 24 CORE DAMPGE 2n COREDAMAGE OK OK OK
.6 COREDAMAGE OK OK 27 COREDAMAGE OK OK 29 COREDAMAGE OK OE 20 COREDAMAGE OK 30 ORE DAMAGE GE 3 CODREDAMAGE 32 COREDAMAGE 33 ORE DAMAGE go ATlAS Dominant core damage sequence for LER 219/90-005
B-56 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 219/90-005 Event
Description:
Trip with ESF 490VAC feeder B and IC train A failure Event Date: 04/21/90 Plant: Oyster Creek INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS 1 .OE+OO SEQUENCE CONDITIONAL PROBABILITY SUNS End State/Initiator Probability CD TRANS 8.8E-05 Total 8.8E-05 ATWS TRANS 3.OE-05 Total 3.OE-05 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence End State Prob N Rec**
18 trans -rx.shutdown pcs arv.chall/trans.-scram -srv.close ISOL CO 7 .1E-05 8 .2E-02
.COND fw/pcs.trans fwci/fw.trans CRD srv.ads 12 trans -rx.shutdown pcs arv.chall/trans.-scram -srv.close ISOL CO 9 .2E-06 1.1E-01
.COND fw/pcs.trans -fwci/fw.trana SOC CC/SOC 15 trans -rx.shutdown pes arv.chall/trans.-scram -srv.close ISOL CD 3.7 E-06 3.9E-02
.COND fw/pcs.trans fwci/fw.trans CRD -srv.ads LPCS -SOC fir ewater 25 trans -rx.shutdown pcs srv.chall/trans.-scram srv.close fw/p CD 2.5E-06 2.4E-01 cs.trans fwci/fw.trans srv.ads 99 trans rx.shutdown ATWS 3.OE-05 1.0E+00
- non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence End State Prob N Rec*-
12 trans -rx.shutdown pcs srv.chall/trans.-scram -srv.close ISOL CO 9 .2E-06 1.1E-01
.COND fw/pcs.trans -fwci/fw.trans SOC CC/SOC 15 trans -rx.shutdown pcs srv.chall/trans.-scram -srv.close ISOL CD 3.7E-06 3.9E-02
.CONO fw/pcs.trans fwci/fw.trans CRD -srv.ads LPCS -SOC fir ewater 18 trans -rx.shutdown pcs srv.chall/trans.-scram -srv.close ISOL CO 7 .1E-05 8.2E-02
.COND fw/pcs.trans fwci/fw.trans CRD srv.ads 25 trans -rx.shutdown pcs srv.chall/trans.-scram srv.close fw/p CO 2 .5E-06 2 .4E-01 cs.trana fwci/fw.trans srv.ads 99 trans rx.shutdown ATWS 3.OE-05 1.OE+00 Event Identifier: 219/90-005
B-57
- non-recovery credit for edited case SEQUENCE MODEL: c :\asp\l989\bwraseal .cmp.
BRANCH MODEL: c :\asp\19S9\oyster . 11 PROBABILITY FILE: c:\asp\1989\bwr-csll.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail trans 2.6E-04 1. OE+00 loop 1. 6E-05 3. 6E-01 loca 3.3E-06 5.OE-O1 rx .shutdown 3.OE-05 1.OE+00 rx. shutdown/ep 3.5E-04 1. OE+O0 PCs 1.7E-01 l.OE+OO srv.chall/trans .-scram 1.OE+OO 1.OE+OO srv.chall/loop.-scram 1 .OE+00 1.0E+00 srv.close 1 .2E-02 1. OE+00 eme rg .power 2.9E-03 S.OE-01 ep. rec 1.6E-01 1. 0E+00 fw/pcs.trans 1 .OE+00 1. OE+00 fwci/fw.trans 2.9E-01 3. 4E-01 fwci/loop 1.OE+OO 1. 05+00 fwci/loca 1.OE-03 3.4 5-01 ISOL.COND l.OE-03 > 1.OE+OO 1.0E+00 > 3.4E-01 Branch Model: l.OF.2 Train 1 Cond Prob: 1 .OE-02 Unavailable Train 2 Cond Prob: 1.05-01 Failed CRD 1.05-02 1.0E+00 1.OE+00 1. OE-02 Branch Model: l.OF.1+opr Train 1 Cond Prob: 1.OE-02 > Unavailable arv.ads 3.7 E-03 7. 15-01 1.OE-02 LPCS 3.OE-04 > 2.OE-03 3.4E-01 Branch Model: 1.OF.2 Train 1 Cond Prob: 3.OE-03 > 2.OE-02 Train 2 Cond Prob: 1 .OE-01 SDC 2.1E-02 > 4.9E-02 3.4E-01 1. OE-03 Branch Model: l.OF.3+ser+opr Train 1 Cond Prob: 3.OE-02 Train 2 Cond Prob: 1.05-01 > Unavailable Train 3 Cond Prob: 3.OE-01 > Unavailable Serial Component Prob: 2.05-02 CC/SDC 1.05-03 > 1.05-02 1.05+00 Branch Model: l.OF.2 Train 1 Cond Prob: 1.05-02 Train 2 Cond Prob: l.OE-0l > Unavailable firewater 1.05+00 1.05+00 2.05-03
- branch model file
- forced Mina rick 08-06-1991 17 :31: 40 Event Identifier: 219/90-005