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Final ASP Analysis - Oyster Creek (LER 219-88-019)
	ML20149K493
Person / Time
Site:	Oyster Creek
Issue date:	05/28/2020
From:	Christopher Hunter; NRC/RES/DRA/PRB
To:	;
	Littlejohn J (301) 415-0428
References
	LER 1988-019-00
	Download: ML20149K493 (6)
	v • d • e

B-10 Accident Sequence Precursor Program Event Analysis LER No.

Event

Description:

Date of Event:

Plant:

219/88-019 Both trains of isolation condensers inoperable due to mechauiiial problems and procedural inadequacies September 2, 1988 Oyster Creek Unit 1 Surmmary Both trains of the isolation condenser system were inoperable for approximately 10 days due to an incorrectly closed isolation valve in one train and a failed motor-operated valve in the other train.

The major impact of the failures is an increase in the likelihood of station blackout sequences over the unavailability period.

This is because the isolation condenser is not dependent on AC power and is important in providing core protection following blackout.

The conditional prob-ability of core damage associated with this event is estimated to be 3.6 x10-6. The relative significance of this event compared with other potential events at Oyster Creek is shown below.

LER 219/88-0 19 1 E-8 I E-7 I E-6 1E-5 I1E-4 IE-3 I E-2 Trip

~L EP Unavail LOOP (360 hrs)

Trip with IC Unavail Event Description On Sept. 2, 1988, at approximately 11:30 a.m., an equipment operator discovered the inboard manual isolation valve was in the incorrect posi-tion (closed) for the "All train of the isolation condenser vent line.

Train "A" of the isolation condenser system was inoperable from Aug. 5, 1988, through Sept. 2, 1988.

The "B" train of the isolation condenser was inoperable from Aug. 24, 1988, through Sept. 2, 1988, due to a motor failure on a steam outlet motor-operated valve and due to leakage past a

B-1Il condensate return isolation valve.

Therefore, both isolation condenser trains were inoperable from Aug. 24, 1988, through Sept. 2, 1988.

An orderly plant shutdown was initiated but was 'terminated when the "A"l train of the isolation condenser had been vented And restored to service at 19:52 on Sept. 2, 1988.

The "B" train was returned to service at 20:17 on Sept. 2, 1988.

The apparent cause of the event was a procedural deficiency.

The administrative controls contained within Procedure 665.5.00.3, "Main Steam Line Isolation Valve Leak Rate Test," were not adequate to prop-erly ensure that all components were returned to the required con-figuration for operation.

Immediate corrective actions were (1) the "A" isolation valve was opened, (2) full system line-ups were performed for both trains, and (3) the "A" isolation condenser was returned to service' after sufficient time had passed to vent noncondensable gases from the tube bundle.

Long-term corrective actions were (1) *the leak rate test procedures will be reviewed and appropriate revisions made and (2) the LER and the associated *incident critique will be incorporated into the required reading program.

Event-Related Plant Design Information The isolation condenser system (ICS) is a standby, high-pressure system for removal of fission product heat from the reactor vessel following a reactor trip and for isolation of the reactor from the main condenser.

The system prevents overheating of the reactor fuel, controls the reactor pressure rise, and limits the loss of reactor coolant through the relief valves.

The ICS is not intended to be activated fast enough to have any effect upon the initial pressure peaks resulting from vari-ous transients such as turbine trip, main steam isolation valve closure, and others.

The system can be activated manually or automatically, and once activated will remain in operation, until manually removed from service.

The system consists of two full-capacity isolation condensers, four AC motor-operated isolation valves, -four DC motor.-operated isolation valves, and three vent lines to the atmosphere.

The valves in the steam inlet lines are normally open so that the tube bundles are at reactor pressure even during standby.

Only the DC motor-operated. condensate isolation valves are normally closed.

The high points in the steam supply lines to each train are vented con-tinuously to the main turbine steam header downstream of. the main steam isolation valves when the plant is operating and the ICS is on standby.

This is done to remove noncondensable gases from the reactor steam, which would otherwise collect *at these high points -in the system and impair the initial actuation and cooling capability of the isolation condensers.

B-12 ASP Modeling Assumptions and Approach The event has been modeled under the assumption that the isolation con-denser system was inoperable for approximately 240 h with no recovery.

No recovery was assumed because it took operators approximately 6.75 h after discovery of the inoperable isolation condenser to restore train

'"A."'

Analysis Results The conditional probability of severe core damage estimated for this event is 3.6 x 10-6.

The dominant core damage sequence is associated with postulated LOOP during the 240-h vulnerability period (p =1.4 x 10-3),

failure of emergency power (p = 2.3 x 10-3), and failure of the isolation condenser (p =1.0). This sequence is highlighted on the following event tree.

B-13 R.

EP' SROEWG lOOPT EPG Ic DRA SAE F4D C)

SW!

LC OC C

END LOOP EPD IIA CIj ADS' FOIRER NO STATE OK O0 OK l

COPE DAMAGE OK OK 4?

C C "E D A A G E

OK 43 COPE DAMAGE OK 44 COPE DAMAGE OK 45 CORE DAMAGE 46 GORIE DAMAC 47 COPE DAMAGE OK OK 08CORE DAMAGE OK OK 51 COPE DAMAGE 52 COPE DAMAGE 53 COPE DAMAGE OK

-K 54 CORE DAMAGE OK 55 COPIE DAMAGE OK OK 56 COPE DAMAG OK 57 COPE DAMAAGE 0K 58 COPE DAMAGE 56 COPE DAMAGE 6o COPE DAMAGE 98 AIWS OK GI OPE DAMAGE G2 OPE DAMAGE OK 63 COPE DAMAIAD 64 COPE DAMAGE 6-7 ATW Dominant Core Damage Sequence for LER 219/88-019

B3-14 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier:

219/88-019 Event

Description:

Both loops of isolation condensers unavailable Event Date:

09/02/88 Plant:

Oyster Creek UNAVAILABILITY, DURATION= 240 NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS LOOP LOCA SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator

6. 3E-02

1. 4E-03

4. OE-04 Probability CD TRANS LOOP LOCA Total ATWS 3.5SE-01 3.2E-06

0. OE+00

3. 6E-06 0.OE+00

0. OE+00 0.OE+00

0. OE+00 TRANS LOOP LOCA Total SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)

Sequence 61 loop emerg.power -rx.shutdown/ep -ep.rec srv.chall/loop.-scram

-srv.close ISOL.CDND 47 loop -emerg.power -rx.shutdown srv.chall/loop.-scram -srv.close ISOL.COND fwci/loop crd srv.ads 18 trans -rx.shutdown pcs srv.chall/trans.-scram -srv.close ISOL

.COND fw/pcs.trans fwci/fw.trans crd srv.ads 53 loop -emerg.power -rx.shutdown srv.chall/loop.-scram srv.close ISOL.CDND fwci/loop srv.ads End State CD CD CD CD P rob 2. 6E-0 6 3.4E5-07

2. 5E-07

2. 1E-07 N Rectt

2. SE-Ol 2. 6E-01 2.4E-01

2. 6E-01

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

Sequence End State 18 trans -rx.shutdown pcs srv.chall/trans.-scram -srv.close ISOL CD

.COND fw/pcs.trans fwci/fw.trans crd srv.ads 47 loop -emerg.power -rx.shutdown srv.chall/loop.-scram -srv.close CD ISOL.CDND fwci/loop crd srv.ads 53 loop -emerg.power -rx.shutdown srv.chall/loop.-scram srv.close CD ISOL.COND fwci/loop srv.ads 61 loop emerg.power -rx.shutdown/ep -ep.rec srv.chall/loop.-scram CD

-srv.close ISOL.CDND

-* non-recovery credit for edited case Note:

For unavailabilities, conditional probability values are differential values added risk due to failures associated with an event.

Parenthetical values indicate compared to a similar period without the existing failures.

SEQUENCE MODEL:

c:\\asp\\sealmod\\bwraseal.cmnp P rob 2.5E-07 3.4E-07 2.1IE-07

2. 6E-06 N Rec*t 2.4E-01

2. 6E-01

2. 6E-01 2. 9E-01 which reflect the a reduction in risk Event Identifier: 219/88-019

B-15 BRANCH MODEL:

PROBABILITY FILE:

c: \\asp\\sealmod\\oyster.sl1) c: \\asp\\sealmod\\bwr csll.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch trans loop loca rx. shutdown rx. shutdown/ep PCs srv.chall/trans.-scram srv.chall/loop.-scram srv.close eme rg.power ep. rec fw/pcs.trans fwc i/ fw.trs fwni/loop fwci/loca ISOL.COND Branch Model:

l.OF.l Train I Cond Prob:

c rd 5 rv.ads lpcs s dc cc/s dc firewater System

2. 6E-04

1. 6E-05

3. 3E-06

3. OE-05

3. 5E-04

1. 7E-01 l.OE+00 l.OE+OO 1.2 E-02

2. 9E-03

1. 6E-01 1.OE+OO 2. 9E-01 I.

OE-s-O l.OE-03 1.OE-02 > l.OE+00 1.OE-02 > Failed 1.OE-02

3. 7E-03