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Final ASP Analysis - Trojan (LER 344-85-002)
	ML20161A153
Person / Time
Site:	Trojan File:Portland General Electric icon.png
Issue date:	06/09/2020
From:	Christopher Hunter; NRC/RES/DRA/PRB
To:	;
	Littlejohn J (301) 415-0428
References
	LER 1985-002-00
	Download: ML20161A153 (5)
	v • d • e

PRECURSOR DESCRIPTION SHEET LER No.:

344/85-002 Event

Description:

Plant Trip, LOFW, and Water Hammer Date of Event:

March 9, 1985 Plant:

Trojan EVENT DESCRIPTION Sequence On the evening of March 9, 1985, the plant was operating at 100% power, steady state.

At 2150 h Pacific Standard Time (PST) a reactor trip occurred from automatic actuation of the RPS because of a main turbine trip.

The turbine trip was caused by spurious indication of excessive vibration in a main turbine bearing.

The RPS and plant safety systems functioned as designed during the transient.

Following the turbine trip, the resulting automatic MEW isolation produced a pressure pulse of -875 psig in the heater drain and feedwater systems as expected.

The pressure surge caused an eroded section of the 14-in.-diam heater drain pump discharge piping to rupture, resulting in the release of a steam-water mixture of '-350*F into the 45-ft (ground-level) elevation of the turbine building.

In addition, fire suppression (deluge) systems, actuated by heat sensors in the turbine building, damaged secondary plant equipment, and one member of the plant operating staff received first and second-degree burns from the high-temperature fluid.

Because of the ruptured piping and steam and water buildup in the turbine building, condenser vacuum was lost -4 min after the reactor trip.

Loss of vacuum rendered the steam dump system inoperable, so the steam-side PORVs were used to control steam pressure and plant tempera-ture.

Makeup water for the SGs was supplied from the condensate storage tank using the AFW system.

The plant was maintained in Mode 3 until 0350 h PST on March 10, 1985, when a forced cooldown, using the PORVs and ANW, was initiated at -50*F/h.

The plant entered Mode 4 at 1020 h PST on March 10, 1985, and the RHR system was placed in service at 1120 h the same day.

The ruptured section of heater drain system piping had experienced severe erosion/corrosion of the pipe wall.

Because the f low out of a normally open 14-in, manual globe valve was directed against the pipe wall, the pipe wall at the rupture location had eroded from a nominal thickness of 0.375 in. to a thickness of -0.098 in.

The pipe is made of A106B carbon steel, and system flow rate is 20 to 24 ft/s at normal operating conditions of -450 psig and 350 0 F.

Based on inspections, the only other section of piping where significant erosion/ corrosion had occurred was, at a 10- to 14-in, expander downstream of a 10-in, con-trol valve.

Minimum wall thickness is still met at that location, however, and repairs will be made during the 1985 outage.

Event Identifier:

344/85-002 E-196

Corrective Action The pipe was replaced.

Plant/Event Data Systems Involved:

MFW, reactor protection, condenser, relief valves Components and Failure Modes Involved:

MFW -

tripped as designed Condenser -

rendered unavailable Turbine bypass -

consequently failed because of loss of condenser Component Unavailability Duration:

NA Plant Operating Mode:

1 (100% power)

Discovery Method:

Operational event Reactor Age:

9.3 years Plant Type:

PWR Comments None MODELING CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate Transient 1.0 No recovery assumed for initial transient Branches Impacted and Branch Nonrecovery Estimate MFW Base case Isolates automatically Secondary-side 0.34 Degraded use of atmospheric dumps depressurization still possible Plant Models Utilized PWR plant Class C Event Identifier:

344/85-002 E-197

CONDITIONAL CORE DAMAGE CALCULATIONS LER Number:

Event

Description:

Event Date.,

Plant:

344/85-002 Plant Trip, LOFW, and Water Hammer 3/9/85 Trojan INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator CV TRANS Total CD TRANS Total ATWS TRANS Total

1.

OOOE+00 Probability

1.

431E-05

1.

431E-05

1.

593E-05

1.

593E -05

3.

OOOE-05

3.

OOOE-05 DOMINANT SEQUENCES End State: CV 125 TRANS -RT AFW MFW HPI(F/B)

End State: CD 127 TRANS -RT AFW MFW HPI(F/B)

End State:

ATWS 128 TRANS RT Event Identifier: 344/85-002 Conditional Probability:

-SS. DEPRESS -COND/MFW Conditional Probability:

SS. DEPRESS Conditional Probability:

5.

O9BE-0b

3.

979E-06

3.

OOOE-05 E-198

SEQUENCE CONDITIONAL PROBABILITIES Sequence End State Seq. Prob Non-Recovn#

102 TRANS -RT -AFW PORV.OR.SRV.CHALL PORV.OR.SRV.RESEAT -HPI HP R/-HPI -SS.DEPRESS -LPR/-HPI.HPR 103 TRANS -RT -AFW PORV.OR.SRV.CHALL PORV.OR.SRV.RESEAT -HPI HP RI-HPI -SS.DEPRESS LPRI-HPI.HPR 104 TRANS -RT -AFW PORV.OR.SRV.CHALL PORY.OR.SRV.RESEAT -HP! HP RI-HP! SS.DEPRESS 109 TRANS -RT -AFW -PORV.OR.SRV.CHALL SS.RELEAS.TERM HP!

119 TRANS -RT AFW MFW -HPI(FIB) -HPRI-HPI PORV.OPEN -SS.DEPRESS

-COND/MFW 120 TRANS -RI AFW MFW -HP! (F/B) -HPR/-HPI PORV.OPEN -SS.DEPRESS CON D/MFW CD CO.

CV CV CD

3.

620E-07

1.

956E-03 7.350E-07 1.956E-03) 5.651E-07 1.008E-03

2.

544E-06

1.

76BE-01

1.

15BE-06 4.636E-02 5.96"'E-07 2.398E-02 121 122 123 124 1 25 126 127 128 TRANS -RT TRANS -RI TRANS -RT TRANS -RT TRANS -RT TRANS -RI TRANS -RI TRANS RI AFW AFW AFW AFW AFW AFN AFW MFW -HP! (FIB)

MFW -HP! (FIB)

MFW HP!(FIB)

MFW HPI(F/B)

-HPRi-HPI PORY.OPEN SS.DEPRESS HPR/-HPI -SS.DEPRESS -CONDINFW HPRI-HPl -SS.DEPRESS CONDIMFW HPR/-HP! SS.DEPRESS

-SS.DEPRESS -COND/NFW

-SS. DEPRESS CONDINFW SS. DEPRESS CD CV CD CD CV CD CD AIWS

9.

035E-07

5.

026E-06

2.

589E-06

3.

923E-06 5.09BE-Ob *

2.

626E-06 3.979E-06 *

3.

OOOE-05

3.619E-02 2.0865E-03

1.

476E-03 12..

236E-03

2. 299E-03

1. 184E-03

1.

795E-03

1.

200E-0 I

dominant sequence for end state 1*non-recovery credit for edited case Note:

Conditional probability values are differential values which reflect the added risk due to observed failures.

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

MODEL-DATA:

b:pwrbtree.cmp b:trojprob.cmp No Recovery Limit BRANCH FREGUENCIESIPROBAB!L!TIES Branch TRANS LOOP LOCA RI RI/LOOP EMERG. POWER AFW AFW/EMERG. POWER Event Identifier: 344/85-002 System

1.

2.

4.

2.

0.

O00E+00

2.

850E-03