RA-24-0183, Automatic Reactor Trip Due to Main Generator Lock-Out

Automatic Reactor Trip Due to Main Generator Lock-Out

ML24204A192
Person / Time
Site:	Harris
Issue date:	07/22/2024
From:	Hoffman D Duke Energy Progress
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
RA-24-0183 LER 2024-001-00
Download: ML24204A192 (1)

Text

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 04/30/2027 (04-02-2024) Estimated burden per response to comply with this mandatory collection request: 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />. Reported lessons

/~""'"°'<.,\\ learned are incorporated into the licensing process and fed back to industry. Send comments regarding burden LICENSEE EVENT REPORT (LER) estimate to the FOIA, Library, and Information Collections Branch (T-6 A10M), U. S. Nuclear Regulatory

, i (See Page 2 for required number of digits/characters for each block) Commission, Washington, DC 20555-0001, or by email to Infocollects.Resource@nrc.gov, and the OMB reviewer

~.,.,, +o~....... at: OMB Office of Information and Regulatory Affairs, (3150-0104), Attn: Desk Officer for the Nuclear Regulatory (See NUREG-1022, R.3 for instruction and guidance for completing this form Commission, 725 17th Street NW, Washington, DC 20503. The NRC may not conduct or sponsor, and a person is http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/) not required to respond to, a collection of information unless the document requesting or requiring the collection displays a currently valid OMB control number.

1. Facility Name 050 2. Docket Number 3. Page Shearon Harris Nuclear Power Plant, Unit 1 00400 31 OF 052

4. Title Automatic Reactor Trip Due to Main Generator Lock-Out

5. Event Date 6. LER Number 7. Report Date 8. Other Facilities Involved

Month Day Year Year Sequential Revision Month Day Year Facility Name Docket Number Number No. 050 05 30 2024 2024 001 00 07 2024--22Facility Name052Docket Number

9. Operating Mode 10. Power Level 1 I 100

11. This Report is Submitted Pursuant to the Requirements of 10 CFR §: (Check all that apply) 10 CFR Part 20 20.2203(a)(2)(vi)10 CFR Part 5050.73(a)(2)(ii)(A)50.73(a)(2)(viii)(A)73.1200(a) 20.2201(b)20.2203(a)(3)(i)50.36(c)(1)(i)(A)50.73(a)(2)(ii)(B)50.73(a)(2)(viii)(B)73.1200(b) 20.2201(d)20.2203(a)(3)(ii)50.36(c)(1)(ii)(A)50.73(a)(2)(iii)50.73(a)(2)(ix)(A)73.1200(c) 20.2203(a)(1)20.2203(a)(4)50.36(c)(2)50.73(a)(2)(iv)(A)50.73(a)(2)(x)73.1200(d) 20.2203(a)(2)(i)10 CFR Part 2150.46(a)(3)(ii)50.73(a)(2)(v)(A)10 CFR Part 7373.1200(e) 20.2203(a)(2)(ii)21.2(c)50.69(g)50.73(a)(2)(v)(B)73.77(a)(1)73.1200(f) 20.2203(a)(2)(iii)50.73(a)(2)(i)(A)50.73(a)(2)(v)(C)73.77(a)(2)(i)73.1200(g) 20.2203(a)(2)(iv)50.73(a)(2)(i)(B)50.73(a)(2)(v)(D)73.77(a)(2)(ii)73.1200(h) 20.2203(a)(2)(v)50.73(a)(2)(i)(C)50.73(a)(2)(vii)

OTHER (Specify here, in abstract, or NRC 366A).

12. Licensee Contact for this LER

Licensee Contact Phone Number (Include area code)

Mike Hershkowitz, Regulatory Affairs (984) 229-2828

13. Complete One Line for each Component Failure Described in this Report

Cause System Component Manufacturer Reportable to IRIS Cause System Component Manufacturer Reportable to IRIS B EANSBUH200 Y

14. Supplemental Report Expected Month Day Year

15. Expected Submission Date No 10 24 2024Yes (If yes, complete 15. Expected Submission Date)

16. Abstract (Limit to 1326 spaces, i.e., approximately 13 single-spaced typewritten lines)

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 is in progress to determine the causal factors leading to the electrical fault. Once the evaluation is complete, a supplemental report will be issued containing the causal factors and corrective actions for this event.

NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 04/30/2027 (04-02-2024) Estimated burden per response to comply with this mandatory collection request: 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />. Reported

,,>A AEG<,l lessons learned are incorporated into the licensing process and fed back to industry. Send comments

~c;.. >

!~o\\ LICENSEE EVENT REPORT (LER) regarding burden estimate to the FOIA, Library, and Information Collections Branch (T-6 A10M), U. S.

~ : Nuclear Regulatory Commission, Washington, DC 20555-0001, or by email to

~ 0 CONTINUATION SHEETInfocollects.Resource@nrc.gov, and the OMB reviewer at: OMB Office of Information and Regulatory

'(,..., 0~..

• • • • • Affairs, (3150-0104), Attn: Desk Officer for the Nuclear Regulatory Commission, 725 17th Street NW, (See NUREG-1022, R.3 for instruction and guidance for completing this form Washington, DC 20503. The NRC may not conduct or sponsor, and a person is not required to http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/) respond to, a collection of information unless the document requesting or requiring the collection displays a currently valid OMB control number.

1. FACILITY NAME 2. DOCKET NUMBER 3. LER NUMBER 050 YEAR SEQUENTIAL REV NUMBER NO.

Shearon Harris Nuclear Power Plant, Unit 1 00400 2024 001 00052 --

I I~ I I I I D NARRATIVE Note: Energy Industry Identification System (EIIS) codes are identified in the text within brackets [].

A. Background

Prior to the event, Shearon Harris Nuclear Power Plant, Unit 1 (HNP), was operating in Mode 1 at 100 percent power. No other structures, systems, or components were inoperable at the time that contributed to the event.

HNP is equipped with two emergency diesel generators (EDGs)[EK DGs], two start up transformers (SUTs)[EA XFMRs]

and two unit auxiliary transformers (UATs)[EA XFMRs]. HNP Technical Specification (TS) 3.8.1.1 limiting condition for operation (LCO) requires two physically independent circuits between the offsite transmission network and the onsite Class 1E distribution system, and two separate and independent EDGs in Modes 1-4. TS 3.8.1.2 LCO requires one circuit between the offsite transmission network and the onsite Class 1E distribution system, and one EDG in Modes 5 and 6.

The onsite AC non-emergency electrical distribution system [EA] provides auxiliary power to buses [BUs] which are divided into trains 'A' and 'B'. Under normal operating conditions, train 'A' receives power through UAT-1A and train 'B' receives power through UAT-1B. During start-up and shutdown conditions, offsite power is supplied to trains 'A' and 'B' through SUT-1A and SUT-1B, respectively. The onsite non-emergency electrical distribution includes the 6.9 kV auxiliary buses 1A, 1B, 1C, 1D, 1E, 1-4A, 1-4AB. Power is carried by six individual bus bars (two per phase), all of which are contained within the same duct enclosure for each bus. This bus arrangement is referred to collectively as a nonsegregated bus [NSBU].

UAT-1B, SUT-1A, and their associated interface equipment were replaced during the spring 2024 refueling outage.

UAT-1A and SUT-1B are original equipment.

This event is reportable per 10 CFR 50.73(a)(2)(iv)(A), as "Any event or condition that resulted in manual or automatic actuation of any of the systems listed in paragraph (a)(2)(iv)(B)... [including] Reactor Protection System [JC]...."

B. Event Description

On May 30, 2024, at 19:49 Eastern Daylight Time, HNP experienced an automatic reactor [RCT] trip due to a lock-out of the main generator [EL GEN](MG). The MG lock-out was caused by an electrical fault in the non-segmented bus at the 6.9 kV bushing box of UAT-1B. Multiple reports were received in the Main Control Room (MCR) of smoke coming from the transformer area. The fire deluge system [KF] activated for UAT-1B. 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 not complex, with all systems responding normally post-trip.

C. Causal Factors

Initial assessment of the fault condition indicates an issue with the potential transformer wiring supplying the load tap changing circuit. A root cause evaluation is in progress to determine the causal factors. Once the evaluation is complete, a supplemental report will be iss ued containing the causal factors for this event.

NRC FORM 366A (04-02-2024) Page 2 3of NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 04/30/2027 (04-02-2024) Estimated burden per response to comply with this mandatory collection request: 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />. Reported

,,>A AEG<,l lessons learned are incorporated into the licensing process and fed back to industry. Send comments

~c;.. >

!~o\\ LICENSEE EVENT REPORT (LER) regarding burden estimate to the FOIA, Library, and Information Collections Branch (T-6 A10M), U. S.

~ : Nuclear Regulatory Commission, Washington, DC 20555-0001, or by email to

~ 0 CONTINUATION SHEET Infocollects.Resource@nrc.gov, and the OMB reviewer at: OMB Office of Information and Regulatory

'(,..., 0~..

• • • • • Affairs, (3150-0104), Attn: Desk Officer for the Nuclear Regulatory Commission, 725 17th Street NW, (See NUREG-1022, R.3 for instruction and guidance for completing this form Washington, DC 20503. The NRC may not conduct or sponsor, and a person is not required to http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/) respond to, a collection of information unless the document requesting or requiring the collection displays a currently valid OMB control number.

1. FACILITY NAME 2. DOCKET NUMBER 3. LER NUMBER 050 YEAR SEQUENTIAL REV NUMBER NO.

Shearon Harris Nuclear Power Plant, Unit 1 00400 2024 001 00052 --

I I~ I I I I D NARRATIVE D. Corrective Actions

UAT-1B has been isolated from the onsite electrical system. HNP was synhcronized to the grid at 13:26 on June 1, 2024. Power is aligned to train 'B' electrical loads through SUT-1B. Additional actions will be determined as needed following completion of the root cause evaluation.

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.

F. Additional Information

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

NRC FORM 366A (04-02-2024) Page 3 3of