ML20147A356

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Final ASP Analysis - Browns Ferry 3 (LER 296-84-012)
ML20147A356
Person / Time
Site: Browns Ferry Tennessee Valley Authority icon.png
Issue date: 05/26/2020
From: Christopher Hunter
NRC/RES/DRA/PRB
To:
Littlejohn J (301) 415-0428
References
LER 1984-012, LER 1984-013, LER 1984-014
Download: ML20147A356 (6)
v • d • e


Text

PRECURSOR DESCRIPTION SHEET LER No.: 296/84-012, -013, -014 Event

Description:

Trip and HPCI Failure Date of Event: November 20, 22 and December 6, 1984 Plant: Browns Ferry 3 EVENT DESCRIPTION Sequence On November 20, 1984, Unit 3 was in startup at 4.5% power. During preparation for performance of RV functional surveillance testing, the licensed reactor operator manually scrammed the unit. In preparation for the test, the pressure set-point controller was lowered to 270 ps ,g, thereby opening -1.5 bypass valves. The RPV water level began decreas-ing due to the increased steam flow through the bypass valves. The operator attempted without success to place condensate boosters' 3B and 3C in service to increase feedwater flow. The pumps' local start switches were found to be set in the Safe/Stop position. Plant! pro-cedures did not have a check-off verification for proper position for the start switches. The operating procedures did not allow for inser-tion of reactor control rods, and the operator felt that raising the pressure set point by closing the bypass valves would cause a pressure spike and drive the reactor water level lower.

When the RPV level indication in the control room level instruments decreased below +11 in. without an automatic scram, the shift. engineer directed the unit operator to scram the reactor manually. (Due to the fact that the reactor was not operating at rated conditions, the level indication in the control room was subsequently determined to be low.

The actual level was determined to be +12 in.)

On November 22, 1984, at 2130 h, the HPCI system was being: te-aligned to the standby readiness condition after reaching a pressure consistent with reset of the HPCI low-pressure isolation. HPCI outboard flow control valve FCV-73-3 could not be opened electrically, and the HPCI system was declared inoperable.

The limitorque valve operator for valve FCV-73--3 was disassembled and visually inspected for damage. Inspection determined that the motor pinion gear had been installed backwards during previous maintenance work. Also, the cable from the power supply to motor shunt field was found to be open.

Event Identifier: 296/84-012 D-9 3

Corrective Action Necessary procedures for startup were revised. The motor pinion gear and mating worm gears on the flow control valve were replaced with new gears in the proper direction. The power cable was repaired.

A 20% random sample of all accessible ECCS valves were inspected on all units. A total of 36 valves were inspected and all of the valves' motor pinion gears were found to be installed in the proper arrangement.

Plant/Event Data Systems Involved:

HPCI, condensate system Components and Failure Modes Involved:

HPCI isolation valve - failed to open on demand Two condensate booster pumps - failed to start on demand (due to improperly positioned start switches)

Component Unavailability Duration: NA Plant Operating Mode: 2 (5% power)

Discovery Method: Operational event Reactor Age: 8.3 years Plant Type: BWR Comments The event has been modeled as if it had occurred from power. Because of the condensate pump switch positioning. In reality, the event could not have occurred above '-50% power.

MODELING CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate LOCA 1 x 10-3 Turbine bypass valve open is modeled as LOCA with nonrecovery equal to typical MSIV failure to close probability Transient 1.0 No recovery assumed Event Identifier: 296/84-012 D-94

Branches Impacted and Branch Nonrecovery Estimate HPCI 1.0 No recovery assumed possible CON Base case Note that base-case failure probability is considered equal to one with base-case nonrecovery estimate equal to 0.34, reflecting nonroutine alignment and or local actuation at the pumps Plant Models Utilized BWR plant Glass C Event Identifier: 296/84-012, -013, -014 D-9 5

CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 296/84-012 Event

Description:

Trip and HPCI Failure Event Date: 11/20/84 Plant: Browns Ferry 3 INITIATING EVENT NON-ýRECOVERABLE INITIATING EVENT PROBABILITIES TRANS 1.OE+00 LOCA 1.OE-03 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CV TRANS 1.IE-06 LOCA 1.3E-07 iTotal 1.3E-06 CD TRANS 1.1E-04 LOCA 1.6E-05 Total I.2E-ý04 ATWS TRANS 2.OE-05 LOCA 2.OE-08 Total 2.OE-05 DOMINANT SEQUENCES End State: CV Conditional Probability: 5.IE-07 155 TRANS SCRAM -SLC.OR.RODS PCS /TRANS SRV.CLOSE FW/PCS.LOCA HPCI RCIC/LOCA -SRV.ADS -COND/FW.PCS

-RHR(SDC)

End State: CD Conditional Probability: 9.7E-05 Event Identifier: 296/84-012 D-9 6

119 TRANS -SCRAM PCS/TRANS SRV.CHALL/TRANS.-SCRAM SRV.CLOSE FW/PCS.LOCA HPCI RCIC/LOCA SRV.ADS End State: ATWS Conditional Probability: 2.OE-05 173 TRANS SCRAM SLC.OR.RODS SEQUENCE CONDITIONAL PROBABILITIES Sequence End State Prob N Rec*I 101 TRANS -SCRAM PCS/TRANS SRV.CHALL/TRANS.-SCRAM -SRV.CLOSE -FW CD 6.SE-06 1.OE-01

/PCS.TRANS RHR(SDC) RHR(SPCOOU)/-LPCI.RHR(SDC) C.I.AND.

Y/RHR (SDC) .RHR(SPCOOL) 119 TRANS -SCRAM PCS/TRANS SRV.CHALL/TRANS.-SCRAM SRV.CLJSE FW CD 9.7E-05

  • 3.4E-01

/PCS.LOCA HPCI RCIC/LOCA SRV.ADS 134 TRANS SCRAM -SLC.OR.RODS PCS/TRANS -SRV.CLOSE FW/PCS.TRANS CV 2.E-07 1.3E-01 HPCI RCIC/TRANS.OR.LOOP -SRV.ADS -COND/FW.PCS -RHR(SDC) 138 TRANS SCRAM -SLC.OR.RODS PCSiTRANS -SRV.CLOSE FW/PCS.TRANS CY 1.2E-07 6.6E-02 HPCI RCIC/TRANS.OR.LOOP -SRV.ADS COND/FW.PCS -LPCS -RHR(

SDC) 155 TRANS SCRAM -SLC.OR.RODS PCS/TRANS SRV.CLOSE FWIPCS.LOCA CY 5.1E-07

-COND/FW .PCS -RHR (SOC) 318 LOCA SCRAM -SLC.OR.RODS PCS/LOCA FW/PCS.LOCA HPCI -SRV.ADS CV 4.3E-08 1.1E-04 COND/FW.PCS -LPCS -RHR(SDC)

  • dominant sequence for end state
    • non-recovery credit for edited case MODEL: b:\bwrctree .cmp DATA: b:\bfprob.cmp No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail TRANS 1.1E-03 1.OE+00 LOOP 1.3E-05 3.4E-01 LOCA 3.3E-06 >3.3E-06 3.4E-01 > 1.OE-03 Branch Model: INITOR Initiator Freq: 3.3E-06 Event Identifier: 296/84-012 D-9 7

SCRAM 4.IE-04 1.0E+00 SLC.OR.RODS I .OE-02 1.0E+00 4.OE-02 PCS/TRANS 1J.E-01 1.OE+00 PCSILOCA 1.OE+00 1.0E+00 SRV .CHALL/TRANS .-SCRAM I.OE+OO 1.0E+00 SRV .CHALL/TRANS .SCRAM I .OE+OO 1.0E+00 SRV .CHALL/LODP .-SCRAM 1.OE+00 1.0E+00 SRV .CHALL/LaaP .SCRAtI 1.OE+00 I .OE+00 SRV .CLOSE 3.6E-02 1.OE+00 EMERG .POWER 5.4E-04 5.IE-01 FW/PCS .TRANS 4 .6E-01 3.4E-01 FW/PCS .LOCA I.OE+00 3.4E-01

,HPCI 1.OE-01 ) 1.OE+00 5.7E-O1 > 1.0E+00 Branch Model- 1.01.1 Train I Cond Prob: 1.OE-O1 > Failed RCIC/TRANS.OR.LOOP 6.7E-02 5.7E-O1 RCIC/LOCA 1.0E+00 1.0E+00

-CRD 1.0E-02 1.OE+00 .4.OE-02 SRV.ADS 6.7E-03 1.0E+00 4.OE-02 COJND/FW .PCS 1.0E+00 3.4E-01 LPCS 3,0E-03 3.4E-01 LPCI(RfWR)/LPCS 4,0OE-04 3.4E-01 RHRSW/LPCS .LPCI .TRANS 5.OE-O1 1.OE+00 4 .OE-02 RHiRSW/LPCS.LPCI .LOOP 5.OE-01 1.0E400 4.OE-02 RHRSW/LPCS.LPCI .LOCA 5.OE-O1 1.OE+00 U.E-02 RHR (SDC) 2.OE-02 3.4E-01 RHR(SDC) /-LPCI 2.OE-02 3.4E-01 RHR (SDC) /LPCI 1.0E+00 1.0E+00 RHR(SPCOOL) /-LPCI .RHR(SDC) 2.OE-02 1.0E+00 RHR(SPCOOL) /LPCI .RHR(SDC) 5.2E-01 I .OE+00 C. .AND.V/RHR(SDC) .RHR(SPCOOL) 1.OE+00 3.4E-01,

      • forced Minarick 04-11-1987 14-.43 :27 Event Identifier: 296/84-012 D- 98
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