05000400/LER-2024-001-01, Automatic Reactor Trip Due to Main Generator Lock-Out

Automatic Reactor Trip Due to Main Generator Lock-Out

ML24297A555
Person / Time
Site:	Harris
Issue date:	10/23/2024
From:	Hoffman D Duke Energy Progress
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
RA-24-0261 LER 2024-001-01
Download: ML24297A555 (1)

LER-2024-001, Automatic Reactor Trip Due to Main Generator Lock-Out

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(A), System Actuation
4002024001R01 - NRC Website

text

(_~ DUKE ENERGY David S. Hoffman Plant Manager Shearon Harris Nuclear Power Plant 5413 Shearon Harris Road New Hill, NC 27562-9300 10 CFR 50.73 October 23, 2024 Serial: RA-24-0261 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 Shearon Harris Nuclear Power Plant, Unit 1 Docket No. 50-400/Renewed License No. NPF-63 Subject: Licensee Event Report 2024-001-01 Ladies and Gentlemen:

Duke Energy Progress, LLC, submits the enclosed Licensee Event Report 2024-001-01 in accordance with 10 CFR 50.73(a)(2)(iv)(A) for Shearon Harris Nuclear Power Plant, Unit 1 (HNP). This event had no significance with respect to the health and safety of the public.

This report is a planned supplement to LER 2024-001-00 submitted on July 22, 2024.

There are no regulatory commitments contained within this report.

Please refer any questions regarding this submittal to Mike Hershkowitz at (984) 229-2828.

Sincerely, ~

7/4--

David S. Hoffman Enclosure: Licensee Event Report 2024-001 -01 cc:

D. Jung, NRC Senior Resident Inspector, HNP N. Jordan, NRC Project Manager, HNP NRC Regional Administrator, Region II

Abstract

Shearon Harris Nuclear Power Plant, Unit 1

00400 3

Automatic Reactor Trip Due to Main Generator Lock-Out 05 30 2024 2024 001 01 10 23 2024 1

100

Mike Hershkowitz, Regulatory Affairs (984) 229-2828 B

EA NSBU H200 Y

B EA NSBU H200 Y

On May 30, 2024, at 19:49 Eastern Daylight Time, Shearon Harris Nuclear Power Plant, Unit 1, experienced an automatic reactor trip from 100 percent power due to lock-out of the main generator caused by an electrical fault in the non-segmented bus at the 6.9 kV bushing box of Unit Auxiliary Transformer (UAT) 1B. UAT-1B was replaced during the 2024 spring refueling outage. Following the reactor trip, the unit was stabilized in Mode 3 at normal operating temperature and pressure. The reactor trip was not complex, with all systems responding normally post-trip. Local observation identified damage to the UAT-1B Y-side non-segregated bus at the connection to the low side bushing box. The reactor trip was reported on May 30, 2024, under 10 CFR 50.72(b)(2)(iv)(B) as an event or condition that results in actuation of the reactor protection system when the reactor is critical. The event had no impact on the health and safety of the public. A root cause evaluation determined site personnel did not adequately evaluate the design of the Daburn 2476/10 cable for use as a potential transformer (PT) sensing cable. The root cause evaluation identified a similar cause and condition was present on the Startup Transformer (SUT) 1A that resulted in a condition prohibited by Technical Specifications. To correct these conditions, the engineering design of UAT-1B and SUT-1A was changed and the PT sensing cable was removed.Page of

3. LER NUMBER YEAR SEQUENTIAL NUMBER REV NO.

052 050 A train of offsite power being declared inoperable and TS 3.8.1.1.a LCO action entry. Local observation identified the nonsegregated bus between the SUT-1A and east side of the Turbine Building was damaged.

C. Causal Factors The UAT-1B and SUT-1A non-segmented bus failures were caused by an electrical fault on the potential transformer (PT) cables associated with the load tap changers. The applied voltage on the PT cables was nominal 4 kilovolts AC, phase to ground, and Daburn 2476/10 cables were used for these applications. Daburn 2476/10 cables use a fluorinated ethylene propylene (FEP) insulation and are rated for 50 kilovolts DC. There is no published AC rating for Daburn 2476/10 cables.

Testing subsequently revealed that new cables fail at 4 kV AC given enough time. The root cause of the UAT-1B and SUT-1A non-segmented bus failures was that site personnel did not adequately evaluate the design of the Daburn 2476/10 cable for use as a PT sensing cable in accordance with procedural guidance.

D. Corrective Actions UAT-1B has been isolated from the onsite electrical system. HNP was synchronized to the grid at 13:26 on June 1, 2024.

Power is aligned to train 'B' electrical loads through SUT-1B. SUT-1A was returned to service to restore A train offsite power operability on May 22, 2024.

To correct the condition, the engineering design of UAT-1B and SUT-1A was changed and the PT sensing cable was removed. To correct the cause, the site will implement a design change for the on-load tap changer voltage sensing cable.

Engineering change refresher training will be provided to qualified personnel at HNP on the selection and evaluation of design inputs.

E. Safety Analysis Following the reactor trip and loss of power from UAT-1B, the power supply was automatically fast transferred from UAT-1B to SUT-1B, maintaining the power supply to the associated safety bus. Loads from UAT-1A were also fast transferred to SUT-1A, in accordance with plant design. The automatic reactor trip was not complex, with all safety systems functioning as designed during and following the reactor trip. This reactor trip had no impact on the health and safety of the public. During the timeframe that the A train of offsite power was inoperable in Modes 1, 2, 3, and 4 on May 4, 2024, through May 22, 2024, the B train of the offsite power system remained operable to fulfill the safety function of providing AC power to HNP. Based upon the availability of the B train of offsite power and the EDGs during this timeframe, this event is not considered to be safety significant.

F. Additional Information There have been no events at HNP similar to the event documented in this LER in the past three years.

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Shearon Harris Nuclear Power Plant, Unit 1 00400 2024 001 01