ML20149K356
| ML20149K356 | |
| Person / Time | |
|---|---|
| Site: | Hatch  |
| Issue date: | 05/28/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1985-018-00 | |
| Download: ML20149K356 (5) | |
Text
PRECURSOR DESCRIPTION AND ANALYSIS LER No.: 321/85-018 Event
Description:
Stuck-Open Relief Valve and HPCI/RCIC Unavailability Date of Event: May 15, 1985 Plant: Hatch 1 EVENT DESCRIPTION Sequence At 2030 h with Unit 1 in steady state power operation at -100% power, plant personnel observed water falling from a control room and HVAC vent (caused by plugged drains) onto an Analog Transmitter Trip System (ATTS)
Division II panel (1H11-P926). This introduced moisture to the ATTS panel that, in turn, resulted in the following: (1) the lifting of the "A" low-low set safety relief valve (SRV) and (2) the failure of an ATTS power supply. The SRV cycled open and was reset three times before it opened a fourth time and remained open at -2118. The operators had already begun a load reduction at 2115. The "A" SRV remained open after its fourth activation; thus, operations personnel complied with proce-dures and manually scrammed the reactor at 2122 h. The MSIVs were closed at 2146 h. Operators made errors in trying to close the SRV initially because of procedure errors.
At -2110 h, the HPCI trip solenoid had energized for -15 min, thus making HPCI inoperable during part of this event. RCIC was out of service for maintenance at this time.
The moisture in the ATTS panel was due to activation of the fire protec-tion deluge system for the "A" control room HVAC filter train.
The RCS stabilized at 250 psig (at 2152 h) before valve closure and RCS pressure rose to 850 psig afterwards. MNW remained available throughout the event.
Corrective Action Plant personnel dried the moisture and rechecked the calibration of all trip units in the ATTS panel to ensure their operability and restored the failed power supply. Plant personnel replaced the charcoal in, and cleaned the drains for, the "A" control room EVAC filter train.
Event Identifier: 321/85-018 E-1 65
Plant/Event Data Systems Involved:
RCIC, HPCI, MSRV, HVAC, electrical panels Components and Failure Modes Involved:
RCIC - out of service HPCI - failed on demand SRV - failed open during event ATTS panel - shorted out from water spray Component Unavailability Duration: NA Plant Operating Mode: 1 (100% power)
Discovery Method: Operational event Reactor Age: 10.7 years Plant Type: BWR Comments
- None, MODELING CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate LOCA Base case Recovery estimate based on experience that these valves typically reset when RCS pressure is reduced Branches Impacted and Branch Nonrecovery Estimate HPCI 0.34 Recoverable or the HPCI pump RCIC 1.0 Not available; out for repair Plant Models Utilized BWR plant Class C Event Identifier: 321/85-018 E-1 66
CONDITIONAL CORE DAMAGE CALCULATIONS LER Number: 321/85-018 Event
Description:
Stuck Open Relief Valve and HPCL/RCIC Unavailability Event Date: 5/15/ 85 Plant: Hatch I INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES LOCA 3.400E-01 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability Cy LOCA 1.460E-05 Total 1.460E-05 CD LOCA 1.841E-03 Total 1.84 1E-03 ATHS LOCA 6.9 14E-06 Total 6.914E-06 DOMINANT SEQUENCES End State: CV Conditional Probability: 9.572E-06 314 LOCA SCRAM -SLC.OR.RODS PCS/LOCA FW/PCS.LOCA HPCI -SRV.ADS -COND/F.PCS -RHR(SDC)
End State: CD Conditional Probability: 1.824E-03 310 LUCA -SCRAM PCS/LOCA FW/PCS.LOCA HPCI RCIC/LOCA SRV.ADS End State: ATHS Conditional Probability: 6.714E-06 332 LOCA SCRAM SLC.OR.RODS Event Identifier: 321/80-018 E-167
SEQUENCE CONDITIONAL PROBABILITIES Sequence End State Seq. Prob Non-RecOVl#
310 LOCA -SCRAM PCS/LGCA FW/PCS.LOCA HPCI RCIC/LOCA SRV.ADS 1.824E-03 4 6.581E-03 314 LOCA SCRAM -SLC.OR.RODS PCS/LDCA FW/PCS.LOCA HPCI -SRV.ADS CD 9.572E-06
- 2.380E-02
-COND/FW. PCS -RHR (SDC) 318 LOCA SCRAM -SLC.OR.RODS PCS/LOCA FW/PCS.LOCA HPCI -SRV.ADS cv 4.926E-06 1.226E-02 COND/FW.PCS -LPCS -RHR(SDC) f dominant sequence for end state if non-recovery credit 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: hatchpro. cmp No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail TRANS 1.142E-03 1.OOOE+00 LOOP 1.305E-05 3.400E-01 LOCA 3.250E -06 3.400E-01 SCRAM 4.IOOE-04 1.OOOE+00 SLC. OR. RODS 1.000E-02 1.OOOE+00 4.OOOE-02 PCS/TRANS 1.700E-01 1.000E+00 PCS/LOCA 1.O0OE+00 1.O0OE+0O SRV. CHALL/TRANS. -SCRAM 1.000E+00 1.OOOE+00 SRV. CHALLITRANS. SCRAM 1.OOOE 400 1.OOOE+00 SRV. CHALL/LOOP. -SCRAM I.000E+00 1.OOOE 400 SRV. CHALL/LOOP. SCRAM 1.OOOE+00 1.OOOE+00 SRY. CLOSE 2.700E-02 1.OOOE+00 EMERG. POWER 5.415E-04 5.1OOE-01I FW/PCS. TRANS 4.600E-01 3.400E-01 FW/PCS. LOCA 1.000OE+00 3.400E-01 HPCI 1.OOOE-01 ) 1.OOOE+00 5.70DE-01 > 3.400E-01 Branch Model: 1.OF.l Train 1 Cond Prob: 1.0OOE-01 ) Failed ACIC/TRANS. OR. LOOP 6.700E-02 5.700E-01 RCIC/LOCA 1.00OE+00 > 1.O0OE+00 1.000E+00 Branch Model: l.OF.I Train 1 Cond Prob: 1.OOOE+00 > Unavailable Event Identifier: 321/85-018 E-1 68
CRD 1.DOOE-02 1.OOOE+00 4.000E-02 SRV. ADS 6.700E-03 1.000OE+00 4.000E-02 CDND/FW. PCS 1.OOOE+00 3.400E-01 LPCS 3.000E-07) 3.400E-01 LPCI (RHR) /LPCS 4.D00E-04 3.400E-01 RHRSK/LPCS. LPCI. TRANS 5.000E-01 1.OO0E+00 4.000 E-02 RHRSW/LPCS. LPCI.LDDP 5.OOOE-01 1.OOOE+00 4.OOOE-02 RHRSW/LPCS. LPCI .LOCA 5.OOOE-01 1.000E+00 4.OOOE-02 RHR(S DC) 2.039E-02 3.400E-01 RHR(SDC) /-LPCI 2.OOOE-02 3.400E-01 RHR (SDC) ILPCI 1.OO0E+00 1.OQOE+00 RHR(SPCOOL) /-LPCI.RHR(SDC) 2.OOOE-02 1.OOOE+00 RHR(SPCODL) /LPCI .RHR(SDC) 5.200E-01 1.O00E+00 C.I.AND.V/RHR(SDC) .RHR(SPCOUL) 1.000E+00 3.400E-01 4** forced Minarick 08-13-1986 04:28:45 Event Identifier: 321/85-018 E-1 69