05000334/LER-2024-001, Offsite AC Power Source Inoperable Due to Breaker Failure Resulting in Condition Prohibited by Technical Specification

Offsite AC Power Source Inoperable Due to Breaker Failure Resulting in Condition Prohibited by Technical Specification

ML24162A104
Person / Time
Site:	Beaver Valley
Issue date:	06/06/2024
From:	Blair B Vistra Operations Company
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
L-24-115 LER 2024-001-00
Download: ML24162A104 (1)

LER-2024-001, Offsite AC Power Source Inoperable Due to Breaker Failure Resulting in Condition Prohibited by Technical Specification

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
3342024001R00 - NRC Website

text

L-24-115 June 6, 2024 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 SUBJECT:

Beaver Valley Power Station, Unit No. 1 Docket No. 50-334, License No. DPR-66 LER 2024-001-00 Beaver Valley Power Station Barry N. Blair Site Vice President P.O. Box4 Shippingport, PA 15077 10 CFR 50.73 Enclosed is Licensee Event Report (LER} 2024-001-00, "Offsite AC Power Source Inoperable due to Breaker Failure Resulting in Condition Prohibited by Technical Specification." This event is being reported in accordance with 10 CFR 50.73(a)(2)(i)(B).

There are no regulatory commitments contained in this submittal. If there are any questions or if additional information is required, please contact Ms. Hope Gilliam, Manager, Regulatory Compliance, at 724-682-4224.

Barry N. Blair Enclosure: Beaver Valley Power Station, Unit No. 1 LER 2024-001-00 cc: NRG Region I Administrator NRG Senior Resident Inspector NRG Project Manager INPO Records Center (via INPO Industry Reporting and Information System)

BRP/DEP Enclosure L-24-115 Beaver Valley Power Station, Unit No. 1 LER 2024-001-00

Abstract

On April 10, 2024, at 2009 with Beaver Valley Power Station, Unit No. 1 (BVPS-1) at 100 percent power in Mode 1, the incoming supply to the normal 4KV 1A bus from the System Station Service Transformer 1A (SSST), breaker 4KVS-1A-1A4, failed to close when demanded from the control room. At the time, Operators were attempting to transfer the 1A normal 4KV bus to offsite power. The breaker was replaced on April 11, 2024, at 1201 to restore operability. The last time breaker 4KVS-1A-1A4 was manipulated occurred on February 20, 2024, at 2048.

A past operability review of this issue determined the failure likely occurred when the breaker was last closed, prior to this event, on February 18, 2024, at 1217 but remained functional until opened on February 20 at 2048. The cause of the breaker failure was due to a loose charging motor and failure of the motor connecting arm bushing.

This event is reportable as a condition prohibited by technical specifications per 10 CFR 50.73(a)(2)(i)(B).

Energy Industry Identification System (EIIS) codes are identified in the text as [XX].

BACKGROUND The BVPS-1 electric power system [EA] design includes an offsite power system and an onsite power system. During normal operation, BVPS-1 station service power is taken from the unit station service transformer (USST) 1C and 1D [EA-XFMR] or may also be taken from the system station service transformers (SSST) 1A and 1B [EA-XFMR]. Electrical buses may be aligned to one source or the other by manipulating circuit breakers. During normal operation, any one of the USSTs or SSSTs or a combination of both may be selected as the preferred source for operation.

The USSTs receive power from the main unit generator output, and the SSSTs receive power from the 138 KV switchyard.

The 4KV Power Distribution System [EA] provides 4160 VAC power to the various normal and emergency 4KV loads within the station. The system consists of four normal buses 1A, 1B, 1C, 1D [EA-BU] and two emergency buses 1AE, 1DF [EB-BU]. Each bus utilizes two supply breakers, one breaker ties the bus to a secondary winding of the USST, and the other ties it to a secondary of the SSST. Manual transfer from unit to system service supply is accomplished from the control room.

Loss of supply to any bus section automatically trips the source breaker and closes the breaker to the alternate source. A provision is also made for manual transfer.

4KVS-1A-1A4 [EA-BKR] function is to close and provide 4KV power from SSST 1A (offsite) through the normal 1A 4KV bus to emergency bus 1AE following a reactor trip. Breaker 4KVS-1A-1A4 is required to close to meet LCO 3.8.1.

Technical Specification (TS) Limiting Condition for Operation (LCO) 3.8.1 requires two qualified circuits between the offsite transmission network and the onsite Class 1E AC Electrical Power Distribution System and two diesel generators (DGs) capable of supplying the onsite Class 1E power distribution subsystem(s) be OPERABLE in Modes 1, 2, 3, and 4. With one offsite circuit inoperable Condition A requires the offsite circuit be restored to operable status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />.

DESCRIPTION OF EVENT

On April 10, 2024, at 2009 during manual transfer activities to transfer 1A normal 4KV bus to offsite power, supply breaker 4KVS-1A-1A4 failed to close when demanded from the control room. Train 'A' offsite power was previously declared inoperable at the start of transfer activities on April 10, 2024 at 1919 and remained inoperable until 4KVS-1A-1A4 replacement on April 11, 2024 at 1201. BVPS-1 was in Mode 1 at 100 percent power.

There was no effect to Unit 2 as a result of this event.

CAUSE OF THE EVENT

The direct cause for the 4KVS-1A-1A4 failure to close was the charging motor was loose, motor connecting arm bushing was failed and the power wires were severed, resulting in the inability to charge the springs. A contributing cause is the procedure did not contain adequate guidance for tightening the charging motor.

The charging motor associated with 4KVS-1A-1A4 had been replaced in April 2019 as part of preventative maintenance. The breaker completed 72 open/close operations satisfactorily from April 2019 until its failure on April 10, 2024.

ANALYSIS OF EVENT

This event is reportable as a condition prohibited by technical specifications per 10 CFR 50.73(a)(2)(i)(B) as the Train A offsite power source was inoperable for approximately 50 days.

The plant risk associated with the BVPS-1 failure of normal bus 4KVS-1A supply breaker 4KVS-1A-1A4 is considered to be very low

safety significance

The change in core damage frequency and the change in large early release frequency calculated for the condition are both very small, even with notable conservative assumptions directly relevant to this issue remaining in the PRA model.

A past operability review was completed and determined that the failure likely occurred the last time 4KVS-1A-1A4 was closed on February 18, 2024 at 1217 but remained functional until opened on February 20, 2024, at 2048 resulting in approximately 50 days of inoperability, which exceeded the LCO allowed outage time for Train A offsite power.

A review of operating logs revealed no entries into LCO 3.8.1 Condition A for the redundant offsite power being inoperable concurrently, therefore no loss of safety function.

CORRECTIVE ACTIONS

1)Breaker 4KVS-1A-1A4 was replaced on April 11, 2024.

2)The preventative maintenance procedure for 4 kV breakers was updated to provide more specific guidance on tightening the charging motor, completed on May 30, 2024.

PREVIOUS SIMILIAR EVENTS

No previous similar events were identified.