05000317/LER-2024-003, A Diesel Generator Inoperable Due to Potential Transformer Failure

A Diesel Generator Inoperable Due to Potential Transformer Failure

ML24250A179
Person / Time
Site:	Calvert Cliffs
Issue date:	09/06/2024
From:	Casey Smith Constellation Energy Generation
To:	Office of Nuclear Reactor Regulation
Shared Package
ML24250A177	List: 05000317/LER-2024-003, A Diesel Generator Inoperable Due to Potential Transformer Failure
References
LER 2024-003-00
Download: ML24250A179 (1)

LER-2024-003, A Diesel Generator Inoperable Due to Potential Transformer Failure

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
3172024003R00 - NRC Website

Abstract

On July 2, 2024, the Main Control Room received alarm 4KV BUS U/V, 480V BUS U/V, 125V DC, Window AA06. Initial investigation using the Alarm Response Manual (ARM) did not identify any abnormal degraded conditions and the 1A Emergency Diesel Generator (EDG) was immediately determined to be operable. Follow-up investigation and troubleshooting identified a failed potential transformer associated with the 17 4KV bus protective relays, which would result in the 1A EDG output breaker tripping open on overcurrent during load sequencing in an emergency scenario. The 1A EDG was promptly declared inoperable on July 8, 2024, and the station entered Technical Specification Condition 3.8.1.B for Unit 1 and 3.8.1.E for Unit 2. After entering the Technical Specification Conditions the site took all requisite Required Actions. The potential transformer was replaced on July 10, 2024, and following a successful surveillance run, the 1A EDG was declared operable on July 11, 2024.

Prior to entering the Technical Specification Conditions and taking the associated requisite Required Actions, in the period between July 2, 2024, and July 8, 2024, the station exceeded the completion time for Technical Specification LCO 3.8.1 for Unit 1 and 3.8.1 for Unit 2; therefore, this event is reportable under 10CFR50.73(a)(2)(i)(B) as an operation or condition which was prohibited by the plant's Technical Specifications.

(See Page 2 for required number of digits/characters for each block)

(See NUREG-1022, R.3 for instruction and guidance for completing this form http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/) Page 4 of 4 E. SAFETY ANALYSIS The subject event satisfies the criteria in NUREG-1022, Revision 3, for any operation or condition that was prohibited by the plants technical specifications. The 4kV Bus U/V, 480 V Bus U/V, 125 VDC received in the Main Control Room on 7/2/2024 at 2 am. The 1A EDG was declared inoperable on 7/8/2024, and the station entered TS Condition 3.8.1.B for Unit 1 and 3.8.1.E for Unit 2. After entering the TS Conditions the site took all requisite Required Actions. The 1A EDG was declared operable on July 11, 2024. However, prior to entering the TS Conditions and taking the associated requisite Required Actions on 7/8/2024, Unit 1 exceeded the completion time for TS Condition 3.8.1.B and the completion time for the subsequently Required Actions.

Additionally, Unit 2 exceeded the completion time for TS Condition 3.8.1.E and the completion time for the subsequently Required Actions. Therefore, this event is reportable pursuant to 10CFR 50.73(a)(2)(i)(B). This event did not result in any actual nuclear safety consequences.

F. CORRECTIVE ACTIONS The potential transformer was replaced on 7/10/2024, and following a successful surveillance run the 1A EDG was declared Operable on 7/11/2024. Training, observations, and procedure change actions have been taken to address the human performance factors that contributed to the event.

G. PREVIOUS OCCURRENCES A review of previous Calvert Cliffs events was performed for the last three years. The review did not identify any events stemming from the failure of a potential transformer which resulted in a condition prohibited by the plants Technical Specifications.

H. COMPONENT FAILURE DATA Component IEEE 803 IEEE 805 FUNCTION ID SYSTEM ID Transformer, Potential.

XPT EK