ML20149K385
| ML20149K385 | |
| Person / Time | |
|---|---|
| Site: | Indian Point  |
| Issue date: | 05/28/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1986-017-00 | |
| Download: ML20149K385 (5) | |
Text
PRECURSOR DESCRIPTION SHEET LER No.:
Event
Description:
Date of Event:
Plant:
247/86-017 Open condenser dump valves cause trip, and one safeguards train fails to start May 28, 1986 Indian Point 2 EVENT DESCRIPTION Sequence Unit 2 was operating at 30% power.
The condenser steam dump con-trol system was switched from the temperature mode to the pressure mode at 1455 h because of erratic behavior observed on temperature controller TC-412J.
At 1556 h, all 12 condenser steam dump valves received an open signal as a
result of faulty steam dump controller PC-404.
This resulted in an increased steam flow and a reduction in reactor coolant temperature and a subsequent SI actuation.
SI train A actuated, resulting in a reactor trip and safeguards actuation; however, train B did not actuate.
SI train A signal resulted in closure of the MSIVs -2.5 s
after the reactor
- trip, effectively ending the high steam-flow condition.
The required functions that did not fully actuate because train B
did not function were containment isolation phase A, train B, and some of the required redundant valving required for SI.
SI train B was successfully actuated at 1607 h,
when the control room operators reset SI.
Resetting SI consists of manually locking in another SI signal and depressing SI reset buttons.
This action actuates parallel contacts in both trains of the SI logic.
Because train B had not been actuated by the first SI signal, the introduction of the second signal initiated a separate SI sequence.
SI equipment was stripped and automatically restarted; all required redundant valves (trains A and B) then operated normally.
Event Identifier:
247/86-017 D-6
Corrective Action The steam dump control system repairs were as follows.
- 1. All electrolytic capacitors and the auto/manual relays were replaced on condenser steam dump controller PC-404, and the controller was recalibrated.
- 2.
Current-to-pneumatic converter PM-404 was replaced with a new unit and calibrated.
- 3.
Temperature controller TC-412J was replaced with a new unit and calibrated.
- 4.
Pressure transmitter PT-404 was calibrated.
Corrective action for the SI system actuation circuit was as follows.
- 1. Relays SIA-2, SL-2, TR-2, and TR-2X were replaced.
The SI actuation log-in was tested and verified operational.
Plant/Event Data Systems Involved:
Turbine bypass and HPI Components and Failure Modes Involved:
Twelve dump valves failed to open during operation HPI, one train failed to autostart Component Unavailability Duration:
NA Plant Operating Mode:
1 (30% power)
Discovery Method:
Operational event Reactor Age:
13.0 years Plant Type:
PWR Comments The event was modeled using a steam line break event tree, consis-tent with similar events identified in the ASP Program.
Because of the limited information in the LER, HPI redundancy was assumed lost.
The model assumed local operator action would be required to close the dump valves had the MSIVs failed to close.
If this was not the case (i.e.,
the dump valves could have been closed from the room) then the core damage probability estimate would have been lower by a factor of at least three.
Event Identifier:
247/86-017 D-7
MODELING CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate SLB 0.34 Steam line isolated on MSIV closure Branches Impacted and Branch Nonrecovery Estimate HPI 0.04 One train failed (recoverable from control room)
Plant Models Utilized PWR plant Class F Event Identifier:
247/86-017 D-8
CONDITIONAL CORE DAMA6E PROBABILITY CALCULATIONS Event Identifier:
247/86-017 Event
Description:
Open Condenser Dump Valve Causes Trip and EBF Train Fails Event Date:
5/2B/B6 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES SLB SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator 3.4E-01 Probability CD SLB I.OE-04 I.OE-04 Total ATNS SLB I.OE-05 1.0E-05 Total DONINANT SEQUENCES End State:
CD Conditional Probability:
9.IE-05 101 SLB -RT -REQ.56.ISO -AFW -HPI PORV.OPEN.DUE.TO.HPI PORV.CLOSURE HPR/-HPI End State:
ATNS Conditional Probability:
I.OE-05 112 SLB RT SEQUENCE CONDITIDNAL PROBABILITIES 101 102 104 Sequence SLB -RT -REQ.SGISO -AFN -HPI PORV.OPEN.DUE.TO.HPI PORV.CLOS URE HPR/-HPI SLB -RT -REQ.SG.ISO AFN -HPI(F/B) -PORV.OPEN HPR/-HPI SLB -RT -REQ.5G.ISO AFW HPI(FIB)
End State Prob CD 9.IE-05 C CD 5.0E-06 CD 4.2E-06 N Rec**
1.9E0 1
- 5.
1E-02 4.BE-02 Event Identifier. 247/86-017 D-9
- 4.IE-02
- dominant sequence for end state Cf non-recovery credit for edited case MODEL:
c:\\asp\\newmodel\\pwrbms]b.txt DATA:
No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recoy Opr Fail SLB Branch Model:
INITOR Initiator Freq:
RT RE.SB.O150 AFW HPi 1,1E-07 > 1.0E+00 0**
1,1E-07 2.5E-04 6.4E-04 i.OE-03 i.OE-03 > I.OE-02 Branch Model:
Train I Cond Train 2 Cond HPI(F/B)
Branch Mode]:
Train.1 Cond Train 2 Cond HPR/-HPI Branch Model:
Train I Cond Train 2 Cond PORV.OPEN REQBA.ADDITION
- 1.
OF.2 Prob:
Prob:
- 1. OF. 2+opr Prob:
Prob.
I.OF.2+opr Prob:
Prob:
1.OE-02 I.OE-01 i.OE-03 1.OE-02 I.OE-O1
- 3.
OE-03
- 3. OE-02 I.OE-O!
i.OE-02
- 8. 3E-04 B.OE-01 6.OE-03
) Unavailable
> I.OE-02
> Unavailable
> 3,0E-02
> Unavailable I.OE400 > 3.E-01
- 1.
2E-01 1.OE+0O 2.7E-01 5.2ZE-01 5.2E-01 5.6E-01 1,0E+00
- 1.
OE+00 1.OE+00 I.
OE.00 4.10E-02
- 4.
OE-02 PORV.OPEN.DUE.TO.HPI PORY.CLOSURE
- forced Austin 09-11-1987 13:46:40 Event Identifier: 247/B6-017 D-1 0