ML20012E058

LER 90-002-00:on 900224,Group I Isolation Occurred When Undervoltage Relay Replaced.Caused by Lack of Recognition of Significance of Having Turbine Reset While Performing Electro Hydraulic Control evolutions.W/900323 Ltr

ML20012E058
Person / Time
Site:	Brunswick
Issue date:	03/23/1990
From:	Harness J, Harris T CAROLINA POWER & LIGHT CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
BSEP-90-0252, BSEP-90-252, LER-90-002-02, LER-90-2-2, NUDOCS 9003300013
Download: ML20012E058 (5)

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Cuoinna Power & Light Coropony  !

Brunswick Nuclear Project P. O.11ox 10429 L Southport, NC 28461 0429 March 23, 1990  ;

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SERI A1,s . BSEP/90 0252  ;

P U.S. Nuclear Regulatory Commission i ATTN Document Control Desk l Washington, DC 20555 llRUNSWit;E STEAM EI.ECTRIC Pl. ANT UNIT 2 I DOCKET NO. 50-324 11 CENSE NO. DPR-62 i I.ICENSEE EVENT REPORT 2-90-002 Gentlemen:

In accordance with Title 10 to the Codo of Federal Regulations, the enclosed Licensee Tvent Report is submittod. This report fullfils the requirement for a written report within thirty (30) days of a reportable occurrence and is in  !

accordance with the format set forth in NUREG-1022 September 1983.

Very truly yours, c f .. t w w .

J. I,. Ilarness General Manager -

Ilrunswick Nuclear Project i

Tit /mcg Enclosuro cc Mr. S. D. Ebneter i Hr. E. G. Tourigny llSEP NRC Resident Offico

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l While Unit 2 was in cold shutdown on 2/24/90, a Group 1 isolation occurred when the undervoltage relay for the Electro Hydraulic Control (EHC) system 125v dc power supply was replaced, following recalibration for Plant Modification 86-058. The event was initiated by mode indication of the main turbine speed selection i switch (EIIS/TA/ SIS) changing from " valves closed to "1800 rpm"

! upon the swap of EHC power supplios when the undervoltage relay was reinstalled. The mode change, coupled with the existing low vacuum condition (cold shutdown), initiated the Group 1 isolation logic.

Investigations into this event have determined that the cause of the event was the lack of recognition of the significance of having the turbine reset while performing EHC evolutions. No further corrective actions are considered necessary for this event.

This event had no safety significance, as the reactor was shutdown for a planned outage.

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Event j Unit 2 Group 1 isolation on low condenser vacuum while replacing I undervoltage relay on EHC 125v de power supply, following recalibration of the relay for PM 86-058.

Initial conditioDE Unit 2 was in cold shutdown. The main turbine was reset at 0818 ,

to allow cycling of a moisture removal valve. An undervoltage i relay, ITE-27S, No. 239U6345, which senses the loss primary power  ;

supply to the Electro Hydraulic Control (EHC) System switches power '

to alternate battery supply, was being replaced following recalibration for Plant Modification (PM)86-058.  ;

Event DescriDtion On 2/24/90, at 1226, a Group 1 isolation occurred when the undervoltage relay for the EHC system 125v dc power supply was being replaced following recalibration. The initial calibration  ;

l of the relay was found not to be acceptable as written due to a ,

l clerical error in the Ritial calibration paperwork. The undervoltage relay was removed for a verification of the .

calibration, using an approved plant procedure.

Upon re-installation of the relay, the EHC turbine high speed logic initiated and the turbine received an 1800 rpm speed signal, which

! caused the turbine stop valves to open. Existing low condenser vacuum, due to plant condition (cold shutdown), resulted in a valid j signal for Group 1 isolation. B21-F019, Main Steam Line Drain .

-Valve, closed as a result of the signal. Other valves associated with the Group 1 signal logic were closed prior to the event. The Group 1 isolation signal was reset at 1240. A work request / job I

order (WR/JO), 90-AEGC1, was generated to determine the reason for l the isolation signal.

! Event Investication As a result of investigations initiated from WR/JO 90-AEGC1, it was determined that the occurrence was a design condition that would occur upon the loss of EHC 125v dc power. PM 86-058 (Unit 2) removed a relay on the turbine trip logic for loss of EHC System 125v de power supply. This removal of this circuit was based on a concern generated by the site Scram Reduction Committee of a i possible single failure of the relay's normally energized contacts b

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that may result in a turbine trip / reactor scram during operation. l As a result of the removal of this relay, the associated turbine trip logic was disabled for loss of 125v dc power supply. With the turbine trip logic disabled, speed logic to the turbine is allowed to initiate, selecting 1800 rpm. This initiates opening of the turbine stop valves. The presence of the existing plant condition of low condenser vacuum, coupled with the turbine speed signal, initiated the designed Group 1 protective isolation. It is also recognized that the same configuration exists in Unit 1 as a result of PM 86-057.

Event Cause The cause of the event was the lack of recognition of the significance of having the turbine reset while performing maintenance / testing / troubleshooting on the EHC system during reactor modes when low condenser vacuum exists. Events of this nature can be expected when the turbine is reset and maintenance on the EHC system is conducted 'in a low condenser vacuum condition.

, The paperwork error that initiated the recalibration was a clerical I error. Calibration data was recorded ao 1 to 2 (instead of .1 to '

.2), which was outside of the acceptance criteria. The individual that had performed the initial calibration was no longer with the company, and the error could not be verified. Recalibration of the relay was performed to ensure that the acceptance criteria had been met. Recalibration data was within acceptable criteria.

l A similar event occurred on Unit 1 in 1988 (LER 1-88-07) following I

reset of the main turbine trip signal resulting from too high reactor water level.

Corrective Actions CP&L has reviewed this event and has determined that no further corrective actions are required. Efforts will be taken to better control EHC maintenance / testing / troubleshooting with the turbine reset; however, due to the lack of safety significance, additional corrective actions are not warranted.

Event Assessment This event had no safety significance. A Group 1 isolation on low condenser vacuum is an Engineered Safety System Feature isolation.

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Full power operation is the most limiting condition for this transient. Even though the isolation for low condenser vacuum is present for all operating conditions, its function is non-ensential during reactor shutdown conditions, as no steam flow is present to be reduced and lead to reactor pressure increases. Since this event would not have occurred during power operation with the loss of EHC power supply (low condenser vacuum signal not present), this event would not have been a credible event under reasonable, alternative conditions.

EIIS CODES Main Turbine EIIS/TA Electro llydraulic Control EIIS/TG 125v de power supply EIIS/EI undervoltage relay EIIS/EI/27 Turbine high speed logic EIIS/TA/ SIS Main Steam Line drain valve EIIS/SE/*

Group 1 protective isolation EIIS/JM

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