ML20149K337
| ML20149K337 | |
| Person / Time | |
|---|---|
| Site: | FitzPatrick  |
| Issue date: | 05/28/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1989-020-00 | |
| Download: ML20149K337 (6) | |
Text
B-224 ACCIDENT SEQUENCE PRECURSOR PROGRAM EVENT ANALYSIS LER No: 333/89-020 Event
Description:
Reactor scram with HPCI system inoperable Date of Event: November 5, 1989 Plant: Fitzpatrick Summary The reactor scrammed from 100% power, and the high-pressure coolant injection (HPCI) system was inoperable. The conditional probability of core damage associated with this event is estimated to be 1.3 x 10-5. The relative significance of this event compared with other potential events at Fitzpatrick is shown below.
Event Description Fitzpatrick was operating at 100% power on November 5, 1989, when the reactor scrammed due to an apparent failure in the electrohydraulic control (EHC) system of the main turbine. HPCI had been previously removed from service when a ground was discovered in the speed control circuit for the HPCI turbine. The plant scrammed on high neutron flux when closure of the turbine control valves caused a pressure spike in the reactor. The rapid pressure rise caused a collapse of voids in the reactor coolant, enhancing moderation and causing a flux increase. The turbine control valve closure was from an unknown signal source (or failure) that probably originated in the EHC system; however, no component failures were found. RCIC was used for reactor vessel makeup.
B-225 Additional Event-Related Information The HPCI system is a high-pressure injection system designed for small-break LOCAs that do not depressurize the reactor. HPCI is an independent system, uses a turbine-driven pump, and automatically initiates on reactor low water level. HPCI can deliver
-5000 gpm of makeup water to the vessel through the feedwater piping.
Closure of the turbine control valves will ordinarily generate an anticipatory scram signal.
Low EHC oil pressure, about 850 psi to the control valves, will indicate that the valves are about to begin closing and will initiate a scram. This provides a margin to core thermal-hydraulic limits during the subsequent transient. During this event, the turbine control valve fast closure relays apparently failed to operate, and the reactor subsequently scrammed on high flux.
ASP Modeling Assumptions and Approach This event has been modeled as a reactor scram with HPCI unavailable during the scram and subsequent recovery actions.
Analysis Results The conditional probability of severe core damage for this event is 1.3 x 10-5. The dominant sequence, highlighted on the following event tree, involves a reactor scram with failure of the power conversion system, SRV challenge and subsequent failure of one of the valves to close, failure of main feedwater, failure to recover FIPCI, and failure to depressurize using ADS.
Other LERs that involved HPCI and/or RCIC inoperability in conjunction with power operations at Fitzpatrick are: 333/89-002, -003, -005, -014, -019, -021, and -023. A chronology of HPCI-related events that occurred during 1989 is shown on the following page.
B-226 Chronology of Fitzpatrick HPCI-related events in 1989 Date Time Power LER Remarks Level 3/2 1330 100 002 HPCI inoperable - failure during related speed test 3/6 1415 100 003 SRV opened momentarily during testing following HPCI inoperability 3/7 1930 100 002 HPCI declared operable 4/12 1225 100 005 HPCI inoperable - speed control circuit failure 4/13 2035 100 005 HPCI declared operable 8/17 0820 100 014 HPCI inoperable due to steam leak-lube oil replaced 8/18 0820 100 014 HPCI declared operable 10/3 0625 100 019 HPCI inoperable due to speed control circuit failure 10/31 1149 100 021, 019 RCIC inoperable - injection valve motor fails 10/31 1958 100 021,019 RClC declared operable 10/31 2110 100 019 HPCI declared operable 11/3 0300 100 019 HPCI inoperable due to speed control circuit failure 11/5 1523 100 020 Reactor scram with HPCI inoperable 11/8 --- 0 019 HPCI mods complete - needs surveillance test 11/12 1734 10 023 Reactor scram at low power during relief valve testing 11/14 -- --- 019 HPCI declared operable
B-227
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IOE T R R H-1 R LPC RN 4R N W4(SP SEO END
~
lENT DONPsAS SOWN IRCA ACNOR SAO LC CI I OE COOLING NO STATE OK OK OW COREDAMJAGE OW OK COREDAMAGE OW OW COREDAMAGE OK OW COREDAMAGE OW OW COREDAMAGE OW OW COREDAMAGE OK COREDAMAGE OW COREDAMAGE COREDAMAGE COREDAMAGE O0 OK CORE DAMAGE DOW OW CORE DAMAGE OK OK CORE DAMAGE OW OW CORE DAMAGE OW CORE DA4MAG OW CORE DAMAGE CORE DAMAGE CORE DAMAGE OW OK CORE DAMAGE OW OW COREDAMAGE OW OW CORE DAMAGE OW OW COREDAMAGE OW OW CORE DAMAGE OW OW COREDAMAGE OW COREDAMAGE OW COREDAMAGE COREDAMAGE COREDAMAGE ATWS Dominant core damage sequence for LER 333/89-020
B-228 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 333/89-020 Event
Description:
Reactor scram with HPCI system inoperable Event Date: 11/05/89 Plant: Fitzpatrick INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS l.OE+00 SEQUENCE CONDITIONAL PROBABILITY SUNS End State/Initiator Probability CD TRANS 1.3E-05 Total 1.3E-05 ATWS TRANS 3.OE-05 Total 3. GE-OS SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER) t Sequence End State Prob N Rec*
28 trans -rx.shutdown pcs/trans srv.chall/trans.-scram srv.close CD 1.2E-05 2 .4E-01 fw/pcs.trans NPCI srv.ads 11 trans -rx.shutdown pcs/trans srv.chall/trans.-scram -srv.close CD 7. 6E-07 l.GE-Gl
-fW/pcs.trans rhr(sdc) rhr (spcool) /rhr(sdc) 99 trans rx.shutdown ATWS 3.GE-05 l.OE+00
- non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER) tt Sequence End State Prob N Rec 11 trans -rx.shutdown pcs/trans srv.chall/trans.-scram -srv.close CD 7. 6E-07 1. GE-0l
-fW/pcs.trans rhr(sdc) rhr(spcool) /rhr(sdc) 28 trans -rx.shutdown pcs/trans srv.chall/trans.-scram srv.close CO 1.2E-05 2 .4E-01 fw/pcs.trans NPCI srv.ads 99 trans rx.shutdown ATWS 3. OE-05 1 . OE+GG
- non-recovery credit for edited case SEQUENCE MODEL: a:\1989\bwrcseal.cmp BRANCH MODEL: a:\1989\fitzpatr.sll PROBABILITY FILE: a:\1989\bwr-csll.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Rec ov Opr Fail trans 3.4E-04 l.OE+OG loop 1.6E-05 3.6E-01 loca 3.3E-06 5.GE-0l rx.shutdown 3.GE-G5 l.OE+GG rx.shutdown/ep 3.5E-04 l.GE+0G pcs/trans 1.7E-01 l.GE+GO srv.chall/trans.-scram l.OE+00 l.GE+GG Event Identifier: 333/89-020
B-229 srv.chall/loop.-scram 1. OE+O0 1. OE+00 srv. close 3.6E-02 1.*OE+00 emerg. power 2. 9E-03 8 *OE-01 ep. rec 1. 6E-01 1. OE+00 fw/pcs .trans 4. GE-01 3.4E-01 fw/pcs. loca 1.OE+00 3.4E-01 HPCI 2.9E-02 > l.OE+00 7.OE-03. > l.OE+00 Branch Model: l.OF.l Train 1 Cond Prob: 2.9E-02 > Unavailable rcic 6.OE-02 7.OE-01 crd l.OE-02 1. OE+00 1 .OE-02 5 rv. ads 3.7E-03 7.1 E-01 3..OE-02 3.pcs 3.0E-03 3.4E-01 ipci (rhr) /lpcs l.OE-03 7.1lE-01 rhr (sdc) 2.1E-02 3.4E-01 1 .OE-03 rhr (sdc) /-lpci 2.OE-02 3.4 E-01 3..OE-03 rhr(sdc)/lpci 1.OE+00 1 *OE+00 1 .OE-03 rhr(spcool) /rhr(sdc) 2.OE-03 3.4E-01 rhr (spcool) I-lpci.rhr (sdc) 2.GE-03 3.4E-0l rhr(spcool) /lpci.rhr(sdc) 9.3E-02 1. OE+00 rhrsw 2.OE-02 3.4E-01 2 .OE-03
- branch model file
- forced Minarick 06-16-1990 13:49:40 Event Identifier: 333/89-020