ML20149K399
| ML20149K399 | |
| Person / Time | |
|---|---|
| Site: | LaSalle  |
| Issue date: | 05/28/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1985-017-00 | |
| Download: ML20149K399 (5) | |
Text
PRECURSOR DESCRIPTION AND ANALYSIS LER No.: 373/85-017 Event
Description:
LOFW and RCIC Trip Date of Event: February 8, 1985 Plant: LaSalle 1 EVENT DESCRIPTION Sequence At 1018 h with Unit 1 at 75% power, the reactor scrammed on low reactor vessel level.
An operator error during maintenance on an instrument valve caused a low feedwater pump suction pressure signal that tripped the 1A and 1B turbine-driven reactor feedwater (TDRFP) pumps. An unsuccessful attempt was made to restart the 1A TDRFP. The motor-driven feed pump was out of service for maintenance. When vessel level reached '-12.5 in., the reactor scrammed (10:18:45), and the recirculation pumps shifted to low speed. When the vessel level reached about -50 in. (1.0:18:48), the HPCs system initiated, the recirculation pumps tripped as required, and the No. 3 DG started. The RCIC system also initiated but tripped because of overspeed.
The MSIVs closed, and other isolations occurred. ADS valve E opened twice to relieve vessel pressure at 1125 psig. Its nominal set point was 1175 psig. Vessel level dropped to approximately -60 in. before it was restored to normal. ROTC was reset and restarted at 10:21:29.
Corrective Action The primary cause of the unit scram was placing a jumper in the feed-water pump NPSH trip circuit that did not serve its intended function.
The jumper was installed utilizing a revision of the print that did not reflect the present system configuration. The circuit had been modified (Mod No. 1-1-82-293), during the September 1984 outage, and the drawing change request had not yet been processed.
Plant/Event Data Systems Involved:
MFW, recirculation pumps, ROTC, MSIVs and ADS., HPCS Components and Failure Modes Involved:
MFW - instrument maintenance error caused trips, of MFW pumps ADS valve - opened twice at incorrect pressure RCIC - failed on demand EventIdentifier: 373/85-017 E-242
Component Unavailability Duration: NA Plant Operating Mode: 1 (75% power)
Discovery Method: Operational event Reactor Age: 3.2 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 PCs5 1.0 No recovery of PCS under given circum-stances RCIC 0.12 Manual recovery from control room Feedwater 0.34 Possible but difficult MFW recovery locally at pumps Plant Models Utilized BWR plant Class C Event Identifier: 373/85-017 E-2 43
CONDITIONAL CORE DAMAGE CALCULATIONS LER Number: 373/85-017 Event
Description:
LOFW and RCIC Trip Event Date: 2/8/85 Plant: LaSalle 1 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS 1.OOOE+00 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CV TRANS 1.305E-07 Total 1. 305E-07 CD TRANS 5.325E-05 Total 5.325E-05 ATWS TRANS 2.034E-05 Total 2. 034E-05 DOMINANT SEQUENCES End State: CV Conditional Probability: 6.510E-OB 134 TRANS SCRAM -SLC.OR.RODS PCSITRANS -SRV.CLOSE FW/PCS.TRANS HPCI RCICITRANS.OR.LOOP -SRV.ADS -CONDIF W.PCS -RHR(SDC)
End State: CD Conditional Probability: 3.O9BE-05 101 TRANS -SCRAM PCS/TRANS SRV.CHALL/TRANS.-SCRAM -SRV.CLOSE -FM/PCS.TRANS RHiR(SDC) RHR(SPCOOL)/-LPCI.RH R(SDC) C.I.AND.VIRHR(SDC) .RHR(SPCOOL)
End State: ATWS Conditional Probability: 2.034E-05 Event Identifier: 373/85-017 E-244
173) TRANS SCRAM SLC.aR.RODS SEQUENCE CONDITIONAL PROBABILITIES Sequence End State Seq. Prob Non-Recov*"
101 TRANS -SCRAM PCS/TRANS SRV.CHALL/TRANS.-SOCRAM -SRV.CLOSE -FW CD J.09BE-05
- 7.630E-02
/PCS.TRANS RHR(SDC) RHR(SPCOOL)/-LPCI.RHR(SDC) C.I.AND.
V/RHR (SDC) .RHR (SPCOOL) 102 TRANS -SCRAM PCS/TRANS SRV.CHALL/TRANS.-SCRAM -SRV.CLOSE FN CD 1.585E-05 33913E-02
/PCS.TRANS -HPCI RHR(SDC) RHR(SPCOOL)/-LPCI.RHR(SDC) C.
II1 TRANS -SCRAM PCS/TRANS SRV.CHALL/TRANS.-SCRAM SRV.CLOSE 4FW CD 1.16b7E-06 7.6b30E-02
/PCS.LOCA RHR(SDC) RHR(SPCOOL)/-LPCI.RHR(SDC) C.I.AND.V
/RHR(SDC) .RHR(SPCOOL) 119 TRANS -SCRAM PCS/TRANS SRV.CHALL/TRANS.-SCRAM SRV.CLOSE FW CD 3.895E-06 1.936E-02
/PCS.LOCA HPCI RCIC/LOCA SRV.ADS 134 TRANS SCRAM -SLC.OR.RODS PCSITRANS -SRV.CLOSE FW/PCS.TRANS CV 6.510E-08
- 8.398E-03 HPCI RCIC/TRANS.OR.LOOP -SRV.ADS -COND/FW.PCS -RHR(SDC) 138 TRANS SCRAM -SLC.OR.RODS PCS/TRANS -SRV.CLOSE FW/PCS.TRANS Cv 3..331E-OB 4.306E -03 HPCI RCIC/TRANS.OR.LOOP -SRV.ADS COND/FN.PCS -LPCS -RHR(
SDC) 155 TRANS SCRAM -SLC.DR.RGDS PCS/TRANS SRV.CLOSE FW/PCS.LOCA CV 2.043E-O8 6.998E-02 HPCI RCIC/LOCA -SRV.ADS -COND/FW.PCS -RHR(SDC) 159 TRANS SCRAM -SLC.OR.RODS PCS/TRANS SRV.CLOSE FW/PCS.LOCA CV 1.046E-08 3.589E-02 HPCI RCIC/LOCA -SRV.ADS COND/FW.PCS -LPCS -RHR(SDC) 173 TRANS SCRAM SLC.OR.RDDS ATWS 2.034E-05 *2.IBIE-01 Idominant sequence for end state Ifnon-recovery credi-t for edited case Note:
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.cmp DATA: b: laslprob.cmp No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr FailI TRANS 1.142E-03 1.000E+00 LOOP 1.305E-05 3.400E-01 LOCA 3.250E -06 3.400E-01 SCRAM 4.IOOE-04 1.OOOE+00 Event Identifier: 373/85-017 E-245
SLC. OR. RODS 1.OOOE-02 1.OOOE+00 4. OOOE-02 PCS/TRANS 1.700E-01 1.OOOE+00 1.OOOE+00 Branch Model: 1.OF.1 Train I Cond Prob: 1.700E-01 >Failed PCSILOCA 1.OOOE+00 1.OOOE+00 SRV.CHALL/TRANO. -SCRAM 1.OOOE+00 1.OOOE+O0 SRV.CHALL/TRANS. SCRAM 1.OOOE+00 1.O0OE+00 SRV.CHALL/LOOP. -SCRAM 1.OOOE+00 1.OO0E+00 SRV. CHALL/LODP. SCRAM 1.OOOE+00 1.OOOE+00 SRV. CLOSE 3.630E-02 1.OOOE+00 EMERG. POWER 2.850E-03 5.100OE-01I FW/PCS. TRANS 4.600E-01 > 1.OOOE+00 3.400E-01 Branch Model: 1.OF.1 Train I Cond Prob: 4.600E-01 > Failed FW/PCS. LOCA 1.OOOE+00 31.400E-01 HPCI 2,.
OOOE-02 3. 400E-01 RCIC/TRANS. OR.LOOP 6.700E-02 >f1.00OE+00 5.700E-01 > 1.200E-01 Branch Model: I.0F.1 Train 1 Cond Prob: 6.700E-01' > Failed RCIC/LOCA 1.O0E+ 00 1.OOOE+00 CR0 1.OOOE-02 1.OOOE+00 4. OOOE-02 SRV. ADS 6.700E-03 I.OOOE+00 4.OOOE-02 COND/FW.PCS 1.000E+00 3. 400E-01 LPCS 2.OOOE-02 3. 400E-01 LPCI (RHR) /LPCS 6.OOOE-04 3. 400E-01 RHRSW/LPCS. LPCI .TRANS I.O0OE+00 1.OOOE+00 RHRSW/LPCS. LPCI .LOOP I.OOOE+00 1.OOOE+00 RHRSW/LPCS. LPCI . LCA 1.O0OE+00 1.OOOE+0O RHR (SDC 2.1OBE-02 3.400E-01 RHR(SDC) /-LPCI 2.000OE-02 3.400E-01 RHR (SDC) /LPCI 1.OO0E+00 1.OOOE+00 RHR (SPCOOLI I-LPCI.RHR (SDC) 2.OOOE-02 1.OOOE+O0 RHR(SPCOOL) /LPCI.RHR(SDC) 5.200E-01 1.OOOE+00 C.I.AND.V4/RHR(SDC) .RHR(SPCOOL) I.OOOE+00 3.400E-01 4** forced Austin 08-13-1986 06: 34:54 Event Identifier: 373/85-017 E-246