05000374/LER-1998-001, :on 980106,indications,isolations & Alarms Occurred Due to Trip of 2B RPS MG Set Output Breaker & Concurrent Tripping of Electrical Protection Assembly. Replaced Circuit Board Containing Overvoltage Relay

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:on 980106,indications,isolations & Alarms Occurred Due to Trip of 2B RPS MG Set Output Breaker & Concurrent Tripping of Electrical Protection Assembly. Replaced Circuit Board Containing Overvoltage Relay
ML20199L978
Person / Time
Site: LaSalle Constellation icon.png
Issue date: 02/05/1998
From: Bukantis L
COMMONWEALTH EDISON CO.
To:
Shared Package
ML20199L973 List:
References
LER-98-001, LER-98-1, NUDOCS 9802100086
Download: ML20199L978 (5)
v • d • e


LER-1998-001, on 980106,indications,isolations & Alarms Occurred Due to Trip of 2B RPS MG Set Output Breaker & Concurrent Tripping of Electrical Protection Assembly. Replaced Circuit Board Containing Overvoltage Relay
Event date:
Report date:
Reporting criterion: 10 CFR 50.73(a)(2)(iv), System Actuation
3741998001R00 - NRC Website
v • d • e

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At 0852, January 6, 1998, numerous Reactor Protection System (RPS) and Primarv Containment Isolaticn System (PCIS) isolations/ half isolation and alarms occurred on LaSalle Unit 2.

This was acaompanied by the

'B" RPS MG SET TROUBLE alarm and loss of indication for "B" RP4 Generator Feed and Output Indicating lights. These indications, isolations and alarms were caused by the trip of the 2B RPS MG set outpot breaker, and concurrent tripping of the Electrical Protection Assembly (EPA) breakers.

On January 7, 1998, at 0916, 2B RPS MG set output breaker tripped again, this time in an off line and unloaded condition (EPA Breakers were open auri RPS bus was being fed from the a s'ernate source).

The trips were caused by a broken solder joint causing an intermittent anc' or high >:esistance connection to the overvoltage relay (59) located on a circuit i

board insidi tne MG set cabinet (mounted on the MG sot).

The circuit board containing the relay waa replaced.

The safety significance of this event is minimal, as the breakers failed in the conservative position as iesigned.

This event is being reported in accordance with the requirements of 10 CR 50.73 (a) (2) (iv) due to an automa'ic actuation of engineered safety features (ESF).

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PLANT AND SYSTEM IDENTIFICATION

General Electric - Boiling Water Reactor Energy Industry Identification Syst6m (EIIS) codes are identified in tha text as (XX).

A.

CONDITION PRIOR TO EVENT

Unit (s) : 2 Event Date: 01/06/18 Evrat Times ^852 Hours O

Reactor Mode (s) : N Power Level (s) : 0%

RCS [AB) Temperature: 80'F 7

Mode (s) Name: Defueled RCJ [AB) Pressure: O PSIG

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B.

DESCRIPTION OP EVENT At 0852 hours0.00986 days <br />0.237 hours <br />0.00141 weeks <br />3.24186e-4 months <br />, January 6, 1998, with Unit 1 in Cold Shutdown and Unit 2 in a detueled condition, Unit 2 Reactor Protection System (RPS) [JC) and Primary Containment Isclation System (PCIS) [JM) isolations / half isolations and alarus occurred. These isolations included: Drywell Pneumatic to Dryweli (EPN 2IN017),

Drywell Pneumatic to Drywell (EPN 2INO31',, Reactor Water Clean Up Inboard Isolation Valve (EPN 2G33-F001), P.eactor Water Clean Up Outboard Isolation Valve (EPN 2G33-F004), Panel 2PL77/T DW bample Inlet Stop Valve (EPN 2CM021B), Panel 2PL76J Sample Oatlet Stop Valve (EPN 2CM025A) and Panel 2PL77J Sample Out.let Stop Valve (EPN 2CM026B). This was accompanied by the "B" RPS MG SET TT.OUBLE alarni and loss of indication for *B" RPS Generator Feed and Output indicating lights.

These indications, isolations and alarms were caused by the trip of the 2B RPS MG set output breaker, and concurrent tripping of tha Electrical Protection Assembly

'(EPA) breakers.

Prompt investigation by an Operations Department Equipment Operator diunovered that the 2B RPS MG Set Output Breaker (EPN 2AP080E-33) wac tripped, and the two RPS EPA Breakers (EPN 2C71-S003D and 2C73-S003D) were also tripped. There was no known work being performed in, around, or on RPS 5

components at the time of this ev.nt.

All Half Scram, Alarms and Isolationn expected upon loss of the 2B RPS 120V AC bus were received and acknowledged.

EPA IK breab r 2C71-S003D was found to be in a tripped conditlon, howeve*, apparently due to mechanical binding of the handle, the trip lever appeared to be in an "untripped" position.

Power to the "B" RPS bus was restored via the alternate g

cource, since there was no indica. tion of a bus / system fault.

2B RPS MG set was

[

examined, and appeared to be fully operation 1, with no abnormal fluct.uation ; in output voltage or frequency. There were no additional alarms or indications Jor either the input or output of the MG set.

All protective devices functioned properly, although failure of an EPA circuit breaker (2C71-S003D) indication mechanism requires that this breaker be replaced. This did not affect the operation ot-diminish the protective function of the breaker.

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After a check to insure there was no equipment damage, or potential for personnel injury, the 7B RPS MG set was restarted for the purpose of troubleshooting, and the MG e6t output circuit breaker wan closed at 1302 hours0.0151 days <br />0.362 hours <br />0.00215 weeks <br />4.95411e-4 months <br />, January 6, 1998, in an unloi,ded condition and allowed to run.

On January 7, 1998, at 0916 hours0.0106 days <br />0.254 hours <br />0.00151 weeks <br />3.48538e-4 months <br />, 2B RPS MG set output circuit breaker tripped again. As before, there was no known

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work being performed in, around, or on RPS components at the time of the event.

The 'lB RPS MG Set Output Breaker (EPN 2AP000E-B3) was closed, and both EPA breakers (EPH 2C71-S003B and 2C71-S003D) were in the *open" position. The

  • B" RPS MG SET TROUBLE alarm was received, along with loss of indication for *B" RPS Generatot Feed and Output indicating lighto, Loads on the

'B" RPS bus were unaffected, as the alternate supply for the bus was providing power per LaSalle Operating Procedure, LOP-RP-01, " Reactor Protection System MG Set Start-Up and Operation."

Investigation revealed that the 2B RPS MG Set output breaker had tripped.

Indications for voltage and frequency were obsersed and found to be stable, with no additional alarms. The MG set was then secured in accordance with applicable atstion procedure. The 2B RPS MG set output breaker tripped due to a failed solder jcint for the overvoltage relay (internal to the MG set) (EPN 2159-RP001B).

The f ailed solder joint appeared as a high reuistance (open) contact in the MG set protective circuitry, and caused the MG set generator output breaker and Electrical Protection Assemblies (EPA) to trip as expected.

This failed solder joint was detected as a part of NWR 980001799-01, performed jointly by Electrical Maintenance Department (EMD) and Operations Analysis Department (OAD),

who detected the high resistance connection during troubleshooting and circuit evaluation. A new circuit board was issued, installed, calibrated and tested successfully. The EPA circuit breaker (EPN 2C71-S003D) was also replaced with a new circuit breaker which was calibrated, installed and successfully tested.

This event being reported in accordance with the requirements of 10 CFR 50.73 (a) (2) (iv) due to an automatic actuation of engineervd safety features (ESP).

C.

CAUSE OF EVENT

The initiating cause of this event was the loss of the

'B" RPS bus as a result of the failure of a solder joint that electrically and mechanical 3y connected the overvoltage relay to a circuit board located inside an enclosure mounted on the MG set.

The f ailure of the solder joint presented an intermittent high resistance connection that was seen as an intermittent "open" in the trip circuit for the M3 set output circuit breaker. The intermittent "open" appeared as would be expected in an overvoltage condition. Testing of the relay and associated circuitry while mounted or. the MG set showed varying resistance levels. Upon removal for fur?.her evaluation, it was observed that the soldered pin connection of the relay to the circuit board did not appear to be an

  • original" factory soldering job (there was no epoxy-like coating on the older joints, wheresa the other solder joints on the board did) and the solder joint was movable, resulting in resistance varying from near zero ohms to near infinite resistance between

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LICENSEE EVENT REPORT (LER)

COMMtNTS REGARDING MURDEN ESTIMATE 10 Tile -

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It could not be determined how the solder joint failed. Maintenance History did not reveal any information regarding a maintenance activity for the overvoltage relay (EPN 2159-RP001B) where the soldered connection may have been changed.

As sucn, the actual cause of the solder joint f ailure cannot be determined.

D...

SAFETf ANALYSIS RPS MG set protective device functions performed as designed during this event,

.and Engineered Safety Feature - (ESP) actuations occurred. The Reactor' Protection System has a " fail safe" design, and on loss of power (as in this case due to MG set trip) protective devices actuate. Tripping of the MG set had no impact on the design requirements of the Reactor Protection System. The EPA anits (EPN

- 2C71-8003B and'2C71-S003D) are connected in series, to that a single failure of

'either unit would continue to provide pru ction for the RPS bus.

The.*B" RPS bus supply was transferred from the RPS MG set to restore power to the

'B" RPS bus.

[Er

CORRECTIVE ACTIONS 1.

~ The circuit board cont.aining the overvoltage relay,' which was the. initial.

cr.use of the event, was replaced by LaSalle EMD, and calibrated as required

_by 07D.

7

.(WR 980001799-01 completed January 10, 1998) 2.

The MG Set output circuit breaker was removed, trip tested, verified'to operate satisfactorily and-re-installed.

(WR 980001799-01 completed January 10,.1998)

, 3 '. -

- EMD and'OAD will perform an inspection of Unit 1 and Unit'2 RPS MG set overvoltage relays and their associated circuit boards and circuitry to insure that the solder joint anon,aly is an isolated event.

(NTS # 374-180-98-SCAQ00001.01) 4.

The component failure-has-been captured by LaSalle's Maintenance Rule

- Program.
- F.

PREVIOUS OCCURRENCRS=

.LER NUMBER.

TITLE 93-018-00 Unit 1 "A" RPS Power Lost Due To A Failed Logic Card Corrective Actions from LER 93-018-00 were unable to prevent this event. The previous LER addressed the failure of a controller card in an Electrical Protection Assembly (EPA).

The failure of this device mounted on a ciJcuit board internal to the Motor Generator set is an unrelated event.

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COMMENTS REGARDING BURDEN EST!MATF 10 TIIE INFORMATION AND RECORDS MANAGEMENT BRANCil TEXT CONTINUATlON (MNBB 7714), U.S. NUCLEAR REGULATORY COMMISSION, WA5tilNGTON, DC 20$$$4001, AND TO Tile PAPERWORK ~

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C.

COMPONENT FAILURE DATA

General Electric (CE) Printed Circuit Board, GE Part Number 3300A03B0918 General Electric (GE) Relay, GE Part Number CR120G20103 4

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