ML18078A497

LER#78-073/01T-0 on 781127:1B Vital Instru Bus Was Lost Causing Reactor Trip.Safety Injection Followed & 1B Diesel #11 Charging & #12 RHR Pumps Failed to Start.Caused by Bad Output Transformer in Supply Inverter

ML18078A497
Person / Time
Site:	Salem
Issue date:	12/11/1978
From:	Kapple A Public Service Enterprise Group
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
Shared Package
ML18078A496	List: ML18078A495 ML18078A497
References
LER-78-073-01T, LER-78-73-1T, NUDOCS 7812140169
Download: ML18078A497 (4)

Text

Report Number: 78-73/0lT Report Date: 12/11/78 Occurrence Date: 11/27/78 Facility: Salem Generating Station Public Service Electric & Gas Company Hancocks Bridge, New Jersey 08038 IDENTIFICATION OF OCCURRENCE:

Loss of lB Vital Instrument Bus CONDITIONS PRIOR TO OCCURRENCE:

Operational Mode 1, Reactor Power 100%

DESCRIPTION OF OCCURRENCE:

At 0455 on ll/27/7S, loss of lB Vital Instrument Bus initiated a reactor coolant loop low flow above P8 reactor trip. The action statement fo.r Technical Specification 3.8.2.1 was implemented.

No. 12. & Na.* 13 Auxiliary Feed Pumps did not start with low steam generator level. No. 12 was manually started by the control room operator. Recovery from the reactor trip was in progress when a high steam flow-low Tave inadvertent safety injection occurred at 0502.

The lo'ss of lB Vital Instrument Bus resulted in inputs from each Steam Generator Hi Steam Flow logic to the Safety Injection logic.

During recovery from the trip, Tave decreased to less than 543°F causing the proper coincident logic for Safety Injection. The safety injection was reset three minutes later. The Safeguards Equip~ent Control System (SEC) was activated by the safety injection signal, however, lB diesel, No. 11 charging pump and No. 12 RHR pump failed to start. The action statements for Technical Specification 3.5.2 and 3.8.1.1.b were implemented. No. 11 RHR pump started from

~EC and was secured after. the safety injection. An attempt was made to restart No. 11 RHR pump at 0630 but the breaker would not close.

Investigation of the bus failure showed that the inverter had failed and the bus was re-energized from the emergency supply solatron transformer. The surveillance requirement for Technical Specification 3.8.1.1.2.a.2 was completed satisfactory by 0756 and lB diesel was declared operable at 1200 upon completion of the 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />. run. Boration commenced at 0825 to bring the RCS to Xenon free cold shutdown condi-tion. At.1315, the plant started cooldown and entered Hot Shutdown

~ode 4 at 2100. RHR was initiated at 2240 and cooldown continued, however, all technical specification action statements were terminated prior to reaching cold shutdown. A detailed report of ECCS actuation will be submitted as a separate report as required by Technical Speci-fication 6.9.2.a. *

".*~ -~

LER 78-73/0iT DESIGNATION OF APPARENT CAUSE OF OCCURRENCE:

The loss of lB Vital Instrument Bus was traced to failure of the output transformer and two regulating resistors in the supply inverter.

The loss of the bus de-energized the "12 RCP breaker open" input r~lays to the solid state protection system . . This erroneous indication of a trippedRCP caused the low flow reactor trip logic to initiate the reactor trip. The failure of lB diesel, No. 11 Charging Pump and No. 12 RHR Pump to start with initiation of safety injection is due to none of this equipment receiving an actuating signal from the lB SEC cabinet which was de-energized by the lB Vital Instrument.Bus failure.

The cause of No. 13 Auxiliary Feed Pump failure to start was traced to misadjustment of the overspeed trip mechanism.

ANALYSIS OF OCCURRENCE:

Technical Specification 3.8.2.1* for onsite power distribution systems requires 115 volt vital instrument buses and inverters operable for lA, lB and lC buses. The action statement reqtdres that with less than the above* complement of AC buses operable, restore the inoperable bus to operable status within 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> or be in at least Hot Standby within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in Cold Shutdown within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />.

The lB Vital Jnstrument Bus was re-energized from the emergency supply solatron transformer and the inverter was returned to .service within 21 .hou~s. The RCS was borated to Xenon free cold shutdown condition and entered Hot Shutdown 17 hours1.967593e-4 days <br />0.00472 hours <br />2.810847e-5 weeks <br />6.4685e-6 months <br /> after the reactor trip. Cc:ioldown continued until all Technical Specification limiting conditions were ter!llinated. The failure of No. lB diesel, No. 11 Charging Pump and No .. 12 RHR Pump to start at the time of safety injection is predictable

• under the circumstances and has been accounted for in the overall plant design of the safety systems. The failure of No. 13 Auxiliary Feed Pump to start appears to be a random failure. Operational test-ing has been done which shows the pump to be fully operational.

CORRECTIVE ACTION:

The failed outp~t transformer and regulatory resistors in the lB Instrument Bus inverter were replaced and tests were run to verify operability. The overspeed trip r~set latch mechanism on No. 13 Auxiliary Feed Pump was re-adjusted to provide more positive latch operation. No. -11 RHR pump breaker wa~ replaced and tested satisfactory.

No. further corrective action is necessary.

• -- .LER 78~73/0lT . "

FAILURE DATA:

Garrett Static Power Conditioning Static Inverter Model Series 1 Transformer/Regulating Model SkVA Mfg.: Airesearch Mfg. Co.

Prepared by A. W. Kappl*e

~~~~~~~=--~~~~~~

Manager/- Salem Generating Station SORC Meeting No .. 75-78

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I During normal ooeration. loss of lB Vital Instrument Bus de-energized "RCP* Breaker l))1J Open" relay in SSPS initiating a reactor trip. Seven minutes later, a safety

~. injection occurred and lB Diesel, No. 11 Charging Pump & No. 12 RHR Pump failed to ITIIJ start. The unit was cooled down to Hot Shutdown condition within 17 hours1.967593e-4 days <br />0.00472 hours <br />2.810847e-5 weeks <br />6.4685e-6 months <br /> and

[)))) remained in this condition throughout investigatiqn *and reoair of the occurrence.

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