ML20147A501

Final ASP Analysis - Columbia (LER 397-87-002)

ML20147A501
Person / Time
Site:	Columbia
Issue date:	05/26/2020
From:	Christopher Hunter Office of Nuclear Regulatory Research
To:
Littlejohn J (301) 415-0428
References
LER 1987-002-00
Download: ML20147A501 (4)

Text

B-1 33 PRECURSOR DESCRIPTION SHEET LER No.:

397/87-002 Event

Description:

Trip with subsequent main steam line flooding Date of Event:

3122/87 Plant:

WNP'2 EVENT DESCRIPTION Sequence While at 71% power, a fuse blew in the feedwater level control system and caused rapid reactor feed pump acceleration and subsequent trip on low suction pressure.

Upon observing feedwater flow reduction, the operators manually tripped the reactor.

When the vessel level dropped to the Level-2 set point (-50 in.),

both high-pressure core spray and reactor core isolation cooling initiated as designed.

The Level-2 set point further caused nuclear steam shutoff supply isolation, an ATWS reactor recirculation pump

trip, and the auto start of the support systems required for HPCS and RCIC.

NSSS isolation required manual vessel pressure control using the main steam safety relief valves.

The trip was complicated when the operators failed to complete the valving sequence required to establish shutdown level control due to the significant attention and effort operators were giving to re-establish containment cooling.

This led to overfilling of the vessel and flooding of the main steam lines.

The operators were diverted by the need to establish containment cooling to prevent a drywell isolation on high pressure.

Recovery from drywell isolation would require reset7 ting the isolation circuit after the level is recovered, starting both the plant service water and reactor closed cooling pumps and opening the cooling water containment isolation valves.

The operators were further distracted when an equipment operator errantly informed control room operators that the RCIC pump had tripped on overspeed, thereby leading operators to rely solely on the safety relief valves for pressure con-trol and the condensate/feedwater system for makeup.

This required vessel depressurization so that the condensate/feedwater system could be used.

Corrective Action Several procedures were reviewed and/or revised.

Additional train-ing was provided to operators specific to recovery from a

Level-2 occurrence.

Further training included review and re-emphasis of main steam isolation to prevent recurrence of main steam line flooding.

As a precautionary measure, the MSRV-4D valve was disassembled and inspected.

The TSW load shedding will be evaluated for modification to shed loads only upon loss of offsite power.

Event Identifier:

397/87-002

B-134 Plant/Event Data Systems Involved:

Reactor feedwater system Main steam RCIC Components and Failure Modes Involved:

Reactor feedwater system -

tripped on spurious zero flow signal Main steam -

lines flooded due to improper valve lineup RCIC -

not failed, though reported failed (and assumed failed once main steam lines flooded)

Component Unavailability Duration:

N/A Plant Operating Mode:

1(71% power)

Discovery Method:

Operational event Reactor Age:

3.2 y Plant Type:

BWR Comments None.

MODELING CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate Transient 1.0 No recovery assumed possible Branches Impacted and Branch Nonrecovery Estimate RCIC 1.0 Assumed faulted although actually unavailable once flooded)

PCS 1.0 Unavailable MFW 1.0

'Inavailable (reported faulted operable -

assumed main steam line Plant Models Utilized BWR plant Class C Event Identifier:

397/87-002

B-135 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier:

397/87-002 Event

Description:

Trip with subsequent main steam line flooding Event Date:

03/22/87 Plant:

WNPSS 2 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator I.OE+00 Probability CD CV TRANS Total TRANS Total 6.5E-06 6.5E-06 1.7E-05 1.7E-05 ATWS TRANS Total 7.OE-06 7.OE-06 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)

Sequence 105 trans -scram PCS/TRANS srv.chall/trans.-scram -srv.close FW/P CS.TRANS -hpci rhr(sdc) rhr(spcool)/-lpci.rhr(sdc)

-c.i.and.v rhrsw(c.i.and.v) 145 trans -scram PCS/TRANS srv.chall/trans.-scram srv.close fw/p cs.loca hpci srv.ads 125 trans -scram PCS/TRANS srv.chall/trans.-scram -srv.close FW/P CS.TRANS hpci RCIC crd srv.ads 106 trans -scram PCS/TRANS srv.chall/trans.-scram -srv.close FW/P CS.TRANS -hpci rhr(sdc) rhr(spcool)/-Ipci.rhr(sdc) c.i.and.v 127 trans -scram PCS/TRANS srv.chall/trans.-scram srv.close -fw/p cs.loca rhr(sdc) rhr(spcool)/-lpci.rhr(sdc)

-c.i.and.v rhrsw(

c.i.and.v) 104 trans -scram PCS/TRANS srv.chall/trans.-scram -srv.close FW/P CS.TRANS -hpci rhr(sdc) rhr(spcool)/-ipci.rhr(sdc)

-c.i.and.v

-rhrsw(c.i.and.v) 913 trans scram -slc.or.rods PCS/TRANS -srv.close FW/PCS.TRANS h

pci RCIC -srv.ads -cond/fw.pcs -rhr(sdc) 917 trans scram -slc.or.rods PCS/TRANS -srv.close FW/PCS.TRANS h

pci RCIC -srv.ads cond/fw.pcs -ipcs -rhr(sdc) 126 trans -scram PCS/TRANS srv.chall/trans.-scram srv.close -fw/p cs.loca rhr(sdc) rhr(spcool)/-lpci.rhr(sdc)

-c.i.and.v

-rhrsw(

c.i.and.v) 963 trans scram slc.or.rods

• • non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)

End State CD Prob N Rec**

2.8E-06 1.2E-01 CD CD CD CD CV CV CV CV 1.7E-06 1.6E-06 1.8E-07 1.2E-07 8.2E-02

2. 4E-01 3.4E-01

7. 6E-02 1.3E-05 2.9E-01 1.4E-06 7.3E-07

5. 7E-07 2.2E-01 1.1E-OI

1. 9E-01 ATWS 7.OE-06 I.OE+00 Sequence End State Prob N Rec**

Event Identifier:

397/87-002

B-136 104 trans -scram PCS/TRANS srv.chall/trans.-scram -srv.close FW/P CS.TRANS -hpci rhr(sdc) rhr(spcool)/-lpci.rhr(sdc) -c.i.and.v

-rhrsw(c.i.and.v) 105 trans -scram PCS/TRANS srv.chall/trans.-scram -srv.close FW/P CS.TRANS -hpci rhr(sdc) rhr(spcool)/-lpci.rhr(sdc) -c.i.and.v rhrsw(c.i.and.v) 106 trans -scram PCS/TRANS srv.chall/trans.-scram -srv.close FW/P CS.TRANS -hpci rhr(sdc) rhr(spcool)/-ipci.rhr(sdc) c.i.and.v 125 trans -scram PCS/TRANS srv.chall/trans.-scram -srv.close FW/P CS.TRANS hpci RCIC crd srv.ads 126 trans -scram PCS/TRANS srv.chall/trans.-scram srv.close -fw/p cs.loca rhr(sdc) rhr(spcool)/-lpci.rhr(sdc) -c.i.and.v -rhrsw(

c.i.and.v) 127 trans -scram PCS/TRANS srv.chall/trans.-scram srv.close -fw/p cs.loca rhr(sdc) rhr(spcool)/-ipci.rhr(sdc) -c.i.and.v rhrsw(

c.l.and.v) 145 trans -scram PCS/TRANS srv.chall/trans.-scram srv.close

_w/p cs.loca hpci srv.ads 913 trans scram -slc.or.rods PCS/TRANS -srv.close FW/PCS.TRANS h

pci RCIC -srv.ads -cond/fw.pcs -rhr(sdc) 917 trans scram -slc.or.rods PCS/TRANS -srv.close FW/PCS`.TRANS h

pci RCIC -srv.ads cond/fw.pcs -lpcs -rhr(sdc) 963 trans scram slc.or.rods Cv CD CD CD Cv CD 1.3E-05 2.9E-01 2.8E-06 1.2E-01 1.8E-07

1. 6E-06 5.7E-07 3.4E-01 2.4E-01

1. 9E-01 1.2E-07 7.6E-02 CD Cv Cv ATWS 1.1E-06 1.4E-06

7. 3E-07 7.OE-06 8.2E-02 2.2E-01

1. IE-OI 1.0E+00

• • non-recovery credit for edited case SEQUENCE MODEL:

BRANCH MODEL:

PROBABILITY FILE:

c:\\asp\\newmodel\\bwrcnew.cmp c:\\asp\\newmodel\\wnp2.new c:\\asp\\newmodel\\bwr_cnew.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail trans loop loca scram slc.or.rods PCS/TRANS Branch Model:

I.OF.1 Train I Cond Prob:

srv.chall/trans.-scram srv.chall/loop.-scram srv.close emerg.power ep.rec FW/PCS.TRANS Branch Model:

I.OF.l Train 1 Cond Prob:

fw/pcs.loca hpci RCIC Branch Model:

I.OF.I Train 1 Cond Prob:

crd srv.ads cond/fw.pcs lpcs lpci(rhr)/lpcs rhr(sdc) rhr(sdc)/-ipci rhr(sdc)/lpci rhr(spcool)/-lpci.rhr(sdc) rhr(spcool)/lpci.rhr(sdc) c.i.and.v rhrsw rhrsw(c.i.and.v)

8. 6E-04 1.7E-05 3.3E-06 3.5E-04 1.OE-02 1.7E-01 > 1.OE+00 1.7E-01 > Unavailable 1.OE+00 1.OE+00 5.9E-02 2.9E-03 1.OE+00 4.6E-01 > 1.OE+00 4.6E-01 > Unavailable 1.OE+00 2.OE-02 6.OE-02 > 1.OE+00 1.OE+00 3.2E-01 5.OE-01 1.OE+00 1.OE+00 1.OE+00 1.0E+00 1.OE+00 1.OE+00 8.0E-01 1.7E-01 3.4E-01 > 1.OE+00 3.4E-01 3.4E-01 7.OE-01 > I.OE+O0 1.OE+O0 7.1E-Ol 3.4E-01 3.4E-01 7.1E-OI 3.4E-01 3.4E-01 1.OE+00 1.OE+00 1.OE+00 1.OE+00 3.4E-01 3.4E-01 1.OE-02 6.OE-02

1. OE-02 3.7E-03 1.OE+00

2. OE-02 6.OE-04 2. 3E-02 2.OE-02 1.OE+00 2.OE-03 5.2E-01 1.OE-03

2. OE-02 5.OE-OI

> Unavailable I.OE-02 I.OE-02 I.OE-03 I.OE-03 1.OE-03 I.OE-03 1.OE-02 2.OE-03 branch model file

• forced Event Identifier:

397/87-002