ML20147A469
| ML20147A469 | |
| Person / Time | |
|---|---|
| Site: | Brunswick  |
| Issue date: | 05/26/2020 |
| From: | Christopher Hunter Office of Nuclear Regulatory Research |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1985-059-00 | |
| Download: ML20147A469 (5) | |
Text
PRECURSOR DESCRIPTION AND ANALYSIS LER No.: 325/85-059 Event
Description:
Reactor Isolation and Scram Plus RCIC and DG Trips Date of Event: November 2, 1985 Plant: Brunswick 1 EVENT DESCRIPTION Sequence At 2326 h Unit 1 primary containment groups 1, 3, and 6 isolations occurred (including MSIV closure) because of a reactor low-level No. 2 signal. The HPCI system and the RCIC system autostarted, and ROIC tripped. The core spray subsystems (A and B) autostarted on a momentary low-level reactor No. 3 signal. The LOOP recirculation pumps tripped off. The ýreactor building ventilation system autoisolated, and the standby gas treatment system autostarted. The RHR system LPCI mode did not automatically initiate because the low-level No. 3 signal did not seal in. Manual initiation capability remained available. Emergency ac D~s 1 through 4 autostarted, and DG 4 tripped. DG 4 was restarted 20 min later. At 2332 *h the unit autoscrammed because of high reactor pressure before the operators were able to reopen the MSIVs to control pressure. A scram recovery was carried out. Reactor safety relief valve A was manually opened to control reactor pressure. The RCIC and condensate feedwater systems were used to control reactor level.
The incurred low-level signals resulted from reactor level instru-mentation falsely sensing low reactor levels when a pressure spike occurred on the instruments' common reference leg. The spike occurred because of an operator's opening the instrument drain valve of the reactor pressure instrument C32-PT-N008 during maintenance.
Corrective Action The involved person was appropriately disciplined. Problems affecting operability of DG 4 and RCIC were resolved, and they were returned to service.
Plant/Event Data Systems Involved:
LPCI`, RCIC, and emergency power Components and Failure Modes Involved:
RCIC - failed~on demand but was recovered LPCI - failed on demand One DG - failed on demand Event Identifier: 325/85-059 E-181
Component Unavailability Duration: NA Plant Operating Mode: 2 (6%, in startup)
Discovery Method: Operational event Reactor Age: 11.1 years Plant Type: BWR Comments None MODELING CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate Transient 1 .0 Nonrecoverable Branches Impacted and Branch Nonrecovery Estimate PC s 1.0 MSIVs had closed MFW 0.34 MSIVs had closed isolating steam from MFW pumps that are turbine-driven RC IC 0.12 Recoverable from the control room, but no indication of the initial trip was available from the unit reactor turbine gage board Plant Models Utilized BWR plant Class C Event Identifier: 325/85-059 E- 182
CONDITIONAL CORE DAMAGE CALCULATIONS LER Number: 325/85-059 Event
Description:
Reactor Isolation and Scram Plus RCIC and. DG Trips Event Date: 11/2/85 Plant: BrunsWiCk 1 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS 1.OOOE+00 SEQUENCE CONDITIONAL PROBABILITY SUNS End State/Initiator Probability CV TRANS 1.035E-06 Total 1.035E-06 CD TRANS 5.979E-05 Total 5.979E-05 ATWS TRANS 2.034E-05 Total 2.034E-05 DOMINANT SEQUENCES End State: CV Conditional Probability: 5.511E-07 134 TRANS SCRAM -SLC.OR.RODS PCS/TRANS -SRV.CLOSE FWIPCS.TRANS HPCI RCIC/TRANS.OR.LOOP -SRV.ADS -COND/F W.PCS -RHR(SDC)
End State: CD Conditional Probability: 2.177E-05 120 TRANS -SCRAM PCS/TRANS -SRV.CHALL/TRANS. -SCRAM -FW/PCS.TRANS RHR(SDC) RHR(SPCOOL)/-LPCI.RHR(SDC) C.1
End State: ATWS Conditional Probability: 2.034E-05 Event Identifier: 325/85-059 E-183
173 TRANS SCRAM SLC.OR.RODS SEQUENCE CONDITIONAL PROBABILITIES Sequence End State Seq. Prob Non-Recovff 101 TRANS -SCRAM PCS/TRANS SRV.CHALL/TRANS. -SCRAM -SRV.CLOSE -FW CD 9.079E-06 7.630E-02 IPCSTRANS RHR(SDC) RHR(SPCOUL)/-LPCI.RHI4RSDC) C.I.AND.
V/RHR(SDC) .RHR(SPCDOOU 102 TRANS -SCRAM PCS/TRANS SRV.CHALL/TRANS.-SCRAM -SRV.CLDSE FW CD 4.411E-06 3.82GE-02 (PCS.TRANS -HPCI RHR(SDC) RHR(SPCOUL)I-LPC[.RHR(SDC) C.
I.AND.V/RHR(SDC) .RHR(SPCOOL) 110 TRANS -SCRAM PCS/TRANS SRV.CHALLITRANS.-SCHAN -SRV.CLOSE FW CD 1.563E-06 8.492E -04
/PCS.TRANS HPCI RCIC/TRANS.OR.LOOP CRD SRV.ADS 119 TRANS -SCRAM PCS/TRANS SRV.CHALL/TRANS.-SCRAM SRV.CLOSE FW CD 7.2B6E-06 3.245E -02
/PCS.LOCA HPCI RCIC/LOCA SRV.ADS 120 TRANS -SCRAM PCS/TRANS -SRV.CHALL/TRANS.-SCRAM -FW/PCS.TRANS CD 2.177E-05 *7.630E-02 RHR(SDC) RBR(SPCDOL)/-LPCI.RHR(SDC) C.I.AND.V/RHR(SDC).R HR(SPCOOL) 121 TRANS -SCRAM PCS/TRANS -SRV.CHALL/TRANS.-SCRAN FW/PCS.TRANS CD 1.058E-05 3.828E-02
-HPCI RHR(SDC) RHR(SPCOUL)/-LPCI.RHR(SDC) C.I.AND.VIRHR (SDC) .RHR (SPCOOL) 129 TRANS -SCRAM PCS/TRANS -SRV.CHALL/TRANS.-SCRAM FW/PCS.TRANS CD 3.74BE-06 8.492E-04 HPCI RCIC/TRANS.OR.LGOP CRD SRV.ADS 134 TRANS SCRAM -SLC.OR.RODS PCS/TRANS -SRV.CLOSE FN/PCS.TRANS CV 5.511E-07 I1.40BE-02 HPCI RCIC/TRANS.OR.LOUP -SRV.ADS -CONDIFW.PCS -RHR(SDC) 138 TRANS SCRAM -SLC.OR.RDDS PCS/TRANS -SRV.CLOSE FW/PCS.TRANS CV 2.836E-07 7.254E-03 HPCI RCIC/TRANS.DR.LOOP -SRV.ADS COND/FW.PCS -LPCS -RHR(
SDC) 155 TRANS SCRAM -SLC.OR.RGDS PCSITRANS SRV.CLUSE FW/PCS.LOCA CV 1.274E-07 1.173E-01 HPCI RCIC/LOCA -SRV.ADS -COND/FW.PCS -RHR(SDC) 159 TRANS SCRAM -SLC.DR.RODS PCS/TRANS SRV.CLOSE FW/PCS.LOCA CV 6.558E-08 6.045E -02 HPCI RCIC/LOCA -SRV.ADS COND/FW.PCS -LPCS -RHR(SDC) 173 TRANS SCRAM SLC.OR.RODS AIWS 2.034E-05 4 2.IBIE-01
- dominant sequence for end state 4*non-recovery credit for edited case Nate:
Conditional probability values are differential values which reflect the added risk due to observed failures.
Parenthetical values indicate a reduction inrisk compared to a similar period without the existing failures.
MODEL: b:bwrctree.cep DAT A: b: brunprob. cup No Recovery Limit BRANCH FREQUENCIESJPRUBABILITIES Event Identifier: 325/B5-059 E-184
Branch System BrachSysemNon-Recov Opr Fail TRANS 1.142E-03 1.000E+00 LOOP 1.305E-05 3.400E-0 I LOCA 3.250E -06 3.400E-01 SCRAM 4.IOOE-04 1.OOOE+00 SLC.OR. RODS 1.000E-02 1.000E+00 4.OOOE-02 PCS/TRANS I.700E-01 >1.0O0E+00 1.OQ0E+00 Branch Model: 1.OF.1 Train 1 Cond Prob: 1.700E-01 1.OOOE+00 PCS/LOCA 1.000E+00 1.OO0E+00 SRV. CHALL/TRANS. -SCRAM 3.000E-01 1.OOOE+00 SRV.CHALL/TRANS. SCRAM 1.000E+00 1.000E+00 SRY. CHALL/LOOP. -SCRAM 3.OOOE-01 1.OOOE+00 SRV.CHALL/LOOP. SCRAM 1.000E+00 1.000E+00 SRV. CLOSE 2.700E-02 1.OOOE+00 EMERG. POWER 2.850E -03 5.IOOE-01 FW/PCS. TRANS 4.600E-01 > 1.OO0E+00 3.400E-01 Branch Model: l.OF.l Train I Cond Prob: 4.600E-01 > 1.000E+00 FN/PCS. LOCA 1.000E+00 3.400E-01 HPC I 1.000E-01 5.700E-01 RCIC/TRANS. OR. LOOP 6.700E-02 > 1.000E+00 5.700E-01 > 1.200E-01 Branch Model: 1.OF.I Train I Cond Prob: 6.700E-02 > 1.000E+00 RCIC/LOCA 1.000E+00 l.OOOE+00 CRD 1.000E-02 1.000E+00 4.OOOE-02 SR V.ADS 6.700E-03 1.000E+00 4.OOOE-02 CDND/FW. PCS 1.O00E+00 3.400E-01 LPCS 3.000E-03 3.400E-01 LPCI(RHR)/LPCS 4.000E-04 3.40OE-01 RHRSW/LPCS.LPCI .TRANS 5.OOOE-0l 1.000E+00 4.OOOE-02 RHRSW/LPCS. LPCI.LOOP 5.000E-01 1.000E+00 4.OOOE-02 RHRSW/LPCS. LPCI. LOCA 5.000E-01 1.000E+00 4.OOOE-02 RHR(SDC) 2.039E -02' 3.400E-01 RHR(SDC) /-LPCI 2.00E -02 3.400E-01 RHR (SDC) /LPCI 1.000E+00 l.OOOE+00 RHR(SPCUOL) /-LPCI.RHR(SDC) 2.00E -02 1.000E+00 RHR(SPCOOL) /LPCI .RHR(SDC) 5.200E-01 1.000E+00 C.1.AND.V/RHR(SDC) .RHR(SPCOOL) 1.000E+00 3.40OE-01
- forced Mi nan ck 08-13-1986 04- 50: 34 Event Identifier: 325/B5-059 E- 185