ML20147A543
| ML20147A543 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 05/26/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1986-013-00 | |
| Download: ML20147A543 (5) | |
Text
PRECURSOR DESCRIPTION SHEET LER No.: 249/86-013 Event
Description:
HPCI and one train of the core spray and LPCI systems are inoperable Date of Event: August 27, 1986 Plant: Dresden 3 EVENT DESCRIPTION Sequence Dresden 3 was in the run mode at 19% power with the HPCI system declared inoperable for repairs (reason not stated). At 0030 h during surveillance testing, the train B CSS full-flow-test valve (3-1042-4B) was discovered to be damaged, so the valve would not close; the B core spray subsystem was also unpressurized. In addition, the LPCI system minimum-flow valve (3-1501-13A) showed a double position indication -
the valve was in midposition. The 2/3 DG failed to close manually onto bus 33-1; however, the generator was able to be synchronized manually to bus 23-1 without incident. In the event of a LOCA, the DG would have closed automatically on bus 33-1. A unit shutdown was begun.
Investigation revealed that valve 3-1042-4B (the "B" pump CSS full-flow-test valve) had a fractured motor-operator housing. The torque switch failed and allowed the motor to drive the valve disk into the valve seat until the motor housing was fractured. The torque switch was incorrectly installed in the reverse direction.
Investigation revealed that the handwheel retaining-ring was dis-engaged and resting atop the handwheel bearing of the Limitorque motor-operator for the LPCI system minimum-flow valve (3-1501-13A). The valve was opened manually.
Investigation revealed that DG 2/3 failed to close onto bus 33-1 because a terminal block screw was loose in junction box 3TB-187. Cold shutdown was achieved at 2007 h.
Corrective Action The torque switch on valve 3-1042-4B (CSS full-flow-test valve) was installed correctly, and the motor housing was replaced. The handwheel retaining ring for the LPCI system minimum-flow valve (3-1501-13A) was correctly installed. The loose terminal block screw in the DG 2/3 junction box 3TB-187 was tightened.
Event Identifier: 249/86-013 D-16
Plant/Event Data Systems Involved:
LPCI, core spray, emergency power, and HPCI Components and Failure Modes Involved:
Pump B CSS full-flow-test valve - failed to close in test LPCI system minimum-flow valve - failed in midposition in test DG 2/3 - failed to close onto bus 33-1 in manual mode operation in test HPCI - inoperable (reason not stated)
Component Unavailability Duration: 15 d Plant Operating Mode: 1 (19% power)
Discovery Method: Testing Reactor Age: 15.6 years Plant Type: BWR Comments Dresden station has three DGs. Each unit has one dedicated DG and the third is a swing DG (2/3) between both. One train of each unit's ECCS is supported by DG 2/3. Failure of DG 2/3 would prevent emergency power to one ECCS train. The SDC system is independent of LPCI so it was not affected.
MODELING CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate Postulated transient Base case nonrecovery Postulated LOOP Postulated LOCA Branches Impacted and Branch Nonrecovery Estimate HPC I 1.0 Out of service and assumed unavailable LPCS Base case Assumed one of two trains fails in test LPCI Base case Assumed one of two trains fails in test Plant Models Utilized BWR plant Class B Event Identifier: 249/86-013 D-1 7
CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 249/86-013 Event
Description:
HPCI and One Train of LPCS and LPCI Are Inoperable Event Date: 8/27/86 Plant: Dresden 3 UNAVAILABILITY, DURATION= 360 NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS 3.IE-01 LOOP 2.OE-03 LOCA 5 .9E-04 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CV TRANS I.4E-Ob LOOP 6.1E-07 LOCA 2.5E-09 Total 2.OE-06 CD TRANS 6.8E-07 LOOP 1.7E-06 LOCA 3.4E-07 Total 2.7E-06 ATWS TRANS O.OE+00 LOOP O0OE+00 LOCA O.OE+00 Total O.OE+00 DOMINANT SEQUENCES End State: CV Conditional Probability: 9.2E-07 Event Identifier: 249/86-013 D-1 8
130 TRANS SCRAM -SLC.OR.RODS PCS/TRANS FW/PCS.TRANS HPCI -SRV.ADS -COND/FW.PCS -SDC End State: CD Conditional Probability: 1.3E-06 213 LOOP -EMERG.POWER -SCRAM SRV.CHALL/LOOP.-SCRAM SRV.CLOSE HPCI SRV.ADS SEQUENCE CONDITIONAL PROBABILITIES Sequence End State Prob N Rec**
109 TRANS -SCRAM PCS/TRANS SRV.CHALL/TRANS.-SCRAM -SRV.CLOSE IS CD 1.8E-07 2.4E-01 OL.COND FW/PCS.TRANS HPCI CRD SRV.ADS 117 TRANS -SCRAM PCS/TRANS SRV.CHALL/TRANS.-SCRAM SRV.CLOSE FW CD 4.2E-07 2.4E-01
/PCS.LOCA HPCI SRVADS 130 TRANS SCRAM -SLC.OR.RODS PCS/TRANS FW/PCS.TRANS HPC! -SRV. CV 9.2E-07
- 2,2E-0I ADS -COND/FW.PCS -SDC 134 TRANS SCRAM -SLC.OR.RODS PCS/TRANS FW/PCS.TRANS HPCI -SRV. CV 4.6E-07 1.,E-01 ADS COND/FW.PCS -LPCS -SDC 147 TRANS SCRAM -SLC.OR.RODS PCS/TRANS FW/PCS.TRANS HPCI SRV. CD 6.2E-0E 2.4E-01 ADS 207 LOOP -EMERG.POWER -SCRAM SRV.CHALL/LOOP.-SCRAM -SRV.CLOSE IS CD 7.9E-08 2.3E-01 OL.COND HPCI CRD SRV.ADS 212 LOOP -EMERG.POWER -SCRAM SRV.CHALL/LOOP.-SCRAM SRV.CLOSE HP CD 7.4E-08 7.7E-02 CI -SRV.ADS LPCS LPCI FIREWTR.OR.OTHER/LPCS.LPCI/LOOP 213 LOOP -EMERG.POWER -SCRAM SRV.CHALL/LOOP.-SCRAM SRV.CLOSE HP CD 1.3E-06 2.3E-01 CI SRVADS 222 LOOP -EMERG.POWER SCRAM -SLC.OR.RODS HPCI -SRV.A[D -LPCS -SD CV 5.9E-07 3.IE-01 C
238 LOOP EMERG.POWER -SCRAM SRV.CHALL/LOOP.-SCRAM -SRV.CLOSE IS CD 8.6E-08 2.6E-01 OL.COND HPCI 240 LOOP EMERG.POWER -SCRAM SRV.CHALL/LOOPF.-SCRAM SRV.CLOSE HP CD 7.2E-08 2.6E-01 CI 309 LOCA -SCRAM PCS/LOCA FW/PCS.LOCA HPCI SRV.ADS CD 3.4E-07 1.2E-01
- dominant sequence for end state
- non-recovery credit for edited case Note: For unavailabilities, conditional probability values are differential values which reflect the added risk due to failures associated with an event. Parenthetical values indicate a reduction in risk compared to a similar period without the existing failures.
SEQUENCE MODEL: c:\asp\newmodei\bwrbtree.cmp BRANCH MODEL: c:\asp\newmodel\dresden.txt PROBABILITY FILE: c:\asp\newmodel\bwr-c.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Event identifier: 249/86-013 D-19
Branch System Non-Recov Opr Fail TRANS 8.6E-04 I.OE+00 LOOP I.7E-05 3.2E-01 LOCA 3.3E-06 5. OE-0I SCRAM 3.5E-04 I.OE+00 SLC .OR .RODS I .OE-02 I.OE+00 4.OE-02 PCS/TRANS 1.7E-01 I.OE+00 PCS/LOCA I.OE+00 I.OE+00 SRV.CHALL/TRANS.-SCRAM I .OE+00 I .OE+00 SRV.CHALL/TRANS.SCRAM I.OE+00 I.OE+00 SRV. CHALL/LOOP.-SCRAM I .OE+00 I .(OE+00 SRV.CHALL/LOOP.SCRAM I.OE+00 IOE+00 SRV.CLOSE 1.6E-02 I.OE+00 EMERG .POWER 2.9E-03 8.OE-01 FW/PCSTRANS 2.9E-01 3.4E-01 FW/PCS.LOCA 4.OE-02 3.4E-01 HPCI 2.9E-02 > 1.OE+00 7.OE-01 > I.OE+00 Branch Model: 1.OF.1 Train I Cond Prob: 2.9E-02 > Unavailable ISOL.COND 2.OE-02 I.OE+00 CRD I.OE-02 I.OE+00 4.OE-02 SRV.ADS 3.7E-03 7.IE-01 4.OE-02 COND/FW.PCS I .OE+00 3.4E-01 LPCS 2.OE-03 > 1.OE-01 3.4E-01 Branch Model: 1.OF.2 Train I Cond Prob: 2,0E-02 > Failed Train 2 Cond Prob: I.OE-0I LPCI I.OE-03 > I.OE-01 7.1E-01 Branch Model: 1.OF.2 Train I Cond Prob: I.OE-02 > Failed Train 2 Cond Prob: I.OE-0I FIREWTR.OR.OTHER/LPCS,.LPCI/TRA 1.OE+00 I.OE+00 FIREWTR.OR.OTHER/LPCS.LPCI/LOO 1.0E+00 I.OE+O0 FIREWTR.OR.OTHER/LPCS.LPCI/LOC I.OE+00 I.OE+00 SrC 2.9E-03 3.4E-01 LPCI (CC) I.OE-03 3.4E-01 LPCI (CC) /LPCI I.OE+00 I.OE+00 C.I.AND.V/LPCI I.OE+00 3.4E-01
- branch model file
- forced Minarick 02-24-1988 12:02:05 Event Identifier:. 249/86-013 D-20