ML20147A529
| ML20147A529 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 05/26/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1984-013-00 | |
| Download: ML20147A529 (6) | |
Text
PRECURSOR DESCRIPTION SHEET LER No.: 346/84-013 Event
Description:
Trip and One Atmospheric Dump Valve Fails to Close Date of Event: September 11, 1984 Plant: Davis-Besse 1 EVENT DESCRIPTION Sequence At 1235 h on September 11, 1984, Davis-Besse experienced a turbine trip from 70% full power, and the turbine trip initiated an anticipatory reactor trip. The posttrip response was normal for a trip from 70% full power. Pressurizer level remained on scale, and minimum RCS pressure was .--1880 psig. The PORV was not operated. Adequate subcooling margin existed at all times. The No. I atmospheric vent valve did not fully reseat on its own, and operators had to lower steam header pressure to get it to reseat.
Because the unit was in the outage burnup window, it was decided to begin the refueling outage. A plant cooldown was initiated.
Later in the cooldown, in mode 3, with one RCP shut down, operators had difficulty balancing pressure in the two OTSGs. At 0109 h on September 12, the station received a SFRCS trip from low pressure in once-through SG 1. This initiated another anticipatory trip of the reactor.
The cause of the trip was an error by personnel who positioned a rotor-lifting beam on the turbine deck in preparation for the refueling outage turbine work. A timber was inadvertently placed into the piping that supports the moisture separator reheater, high-water-level switch. The bump caused the switch to actuate. The switch is intended to cause the turbine to be isolated when the water level gets too high in the moisture separator reheater. This is to protect the turbine from damage that would occur if water hit the blades. The switch caused the turbine to trip, which initiated a reactor trip.
The cause of the No. 1 atmospheric vent valve's not fully reseating was determined to be in the valve control circuit, specifically the air control solenoids that are in need of replacement or refurbishment.
Event Identifier: 346/84-013 D-191
The cause of the SFRCS trip on September 12, 1984, was that the plant shutdown and cooldown procedure did not adequately cover an RCS cooldown using the turbine-driven main feed pumps. Use of this pump is necessitated by the inavailability of the startup feedpump due to pipe-break concerns.
Corrective Action The maintenance workers who actuated the switch were counseled on being more careful around operating equipment.
Permanent guardrails were to be installed around the MSR high-level switches. A two-out-of -three trip scheme for the MSR high-level trip was to be provided by adding two additional level switches to the exist-ing sensing leg, with guardrails around these additional level switches.
The atmospheric vent air-control solenoid valves were replaced during the 1984 refueling outage.
The plant shutdown and cooldown procedure was modified to provide guidance for an RCS cooldown using the turbine-driven main feed pump.
Plant/Event Data Systems Involved:
Secondary-side relief Components and Failure Modes Involved:
Atmospheric vent valve - failed to close on demand Component Unavailability Duration: NA Plant Operating Mode: 1 (70% power)
Discovery Method: Operational event Reactor Age: 7.1 years Plant Type: PWR Comments None MODELING CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate Transient 1.0 Not recoverable following reactor trip Event Identifier: 346/84-013 D-192
Branches Impacted and Branch Nonrecovery Estimate Secondary-side 0.12 Nonroutine recovery from control room release terminated by operators lowering steam header pressure Secondary-s ide 0.12 Nonroutine recovery from control room release terminated by operators lowering steam header given MFW success pressure Plant Models Utilized PWR plant Class B Event Identifier: 346/84-013 D-193
CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 346/84-013 Event
Description:
Trip and One Atmospheric Dump Valve Fails to Close Event Date: 9/11/84 Plant: Davis-Besse INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS 1.0E+00 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CV TRANS 6.BE-05 Total 6.8E-05 CD TRANS 4.1E-06 Total 4.1E-06 ATWS TRANS 3.OE-05 Total 3.OE-05 DOMINANT SEQUENCES End State: CV Conditional Probability: 5.7E-05 109 TRANS -RT -AFW -PORV.OR.SRV.CHALL SS.RELEAS.TERM HPI End State: CD Conditional Probability: 1.2E-06 126 TRANS -RT AFW MFW HPI(F/B) -SS.DEPRESS CONO/MFW End State: ATWS Conditional Probability: 3.OE-05 Event Identifier: 346/84-013 D-194
128 TRANS RT SEQUENCE CONDITIONAL PROBABILITIES Sequence End State Frob N Rec**
101 TRANS -RT -AFW PORV.OR.SRV.CHALL -PORV.OR.SRV.RESEAT SS.RELE Cv 5.OE-06 6.2E-02 AS.TERt4 HP!
103 TRANS -RT -AFW PORV.OR..SRY.CHALL PORY.OR.SRV.RESEAT -HPI HP CD 1.1E-06 2.8E-02 R/-HPI -SS.DEPRESS LPR/-HPI.HPR 104 TRANS -RT -AFW PORY.OR.SRV.CHALL PORV.OR.SRV.RESEAT -HP! HP CD 6.OE-08 2.8E-02 RI-HP! SS.DEPRESS 109 TRANS -RT -AFW -PORV .OR .SRV .CHALL SS .RELEAS .TERM HP! Cv 5.7E-05
- 6.2E-02 120 TRANS -RT AFW NFW -HPI(F/B) -HPR/-HPI PORV.OPEN -SS.DEPRESS CD 2.8E-07 3.1E-02 COND/MFW 122 TRANS -RT AFW MFW -HP! (F/B) HPR/-HPI -SS.DEPRESS -COND/MFW CV 21.3E-06 3 .4E-02 123 TRANS -RT AFW MFW -HPI(F/B) HPR/-HPI -SS.DEPRESS COND/MFW CO 1.2E-06 1.7E-02 124 TRANS -RT AFW MFW -HPI(F/B) HPR/-HPI SS.DEPRESS CD 1.3E-07 5.1 E-02 125 TRANS -RT AFW MFWHPI(F/B) -SS.DEPRESS -COND/MFW Cv 2 .4E-06 3.2E-021 126 TRANS -RT AFW MFWHP! (F/B) -SS.DEPRESS COND/KFW CD 1.2E- 06
- 1.21-0 1
- dominant sequence for end state
- non-recovery credit for edited case MODEL: b:\pwrb tree .cmp DATA: b:\davispro. .cmp No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail TRANS I. E-03 1.OE+00 LOOP 2.3E-05 3.4E-01 LOCA 4.2E-06 3.4E-01 RT 2.5E-04 1.2E-01 RT/LOOP 0.OE+00 1.0E+00 EMERG .POWER 24.9E-03 5.1E-01 AFbJ 5.OE-03 2.7E-01 AFW/EMERG .POWER 5.OE-03 2.7E-01 MFW 2.OE-01 3.4E-01 PORY DR .SRV .CHALL 8.OE-02 1.OE+00 PORV .OR .SRV .RESEAT 1.OE-02 5.OE-02 PORV .OR.SRV .RESEAT/EMERG .POWER 1.OE-02 5.OE-02 SBS.RELEAS .TERM 1.5E-02 > 1.OE+00 3.4E-01 > 1.2E-01 Branch Model: 1.OF.1 Event Identifier: 346/84-013 D- 195
Train 1 Cond Prob: 1.5E-02 ) Failed SS .RELEAS .TERM/-MFW 1.5E-02 > 1.OE+0O 3.4E-01 > 1.2E-01 Branch Model: 1.0F.1 Train 1 Cond Prob: 1.5E-02 ) Failed HPI 1.OE-03 5.2E-01 HP! (F/B) 1.OE-03 .5.2E-01 4.OE-02 HPR/-HPI 3.OE-03 5.6E-01 4.OE-02 PORV .OPEN 1.OE-02 I .OE+00 SS .DEPRESS 3.6E-02 1.OE+00 COND/MFW 1.OE+00 3.4E-01 LPI/HPI 1.OE-03 3A.E-01 LPR/-HPI .HPR 6.7E-01 1.OE+00 LPR/HPI 1.OE-03 I.OE+00
- .forced Minar ick 04-12-1987 10 :47 :38 Event Identifier: 346/84-013 D-196