05000416/LER-2022-001, For Grand Gulf Nuclear Station, Unit 1, Manual Reactor Trip Due to the Loss of Balance of Plant Transformer 23

For Grand Gulf Nuclear Station, Unit 1, Manual Reactor Trip Due to the Loss of Balance of Plant Transformer 23

ML22241A113
Person / Time
Site:	Grand Gulf
Issue date:	08/29/2022
From:	Hardy J Entergy Operations
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
GNRO2022-00028 LER 2022-001-00
Download: ML22241A113 (6)

LER-2022-001, For Grand Gulf Nuclear Station, Unit 1, Manual Reactor Trip Due to the Loss of Balance of Plant Transformer 23

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(ix)(A)
4162022001R00 - NRC Website

text

Entergy Operations, Inc.

entergy P.O. Box 756 Port Gibson, Mississippi 39150

Jeffery A. Hardy Manager Regulatory Assurance Grand Gulf Nuclear Station Tel: 802-380-5124

10 CFR 50.73

GNRO2022-00028

August 29, 2022

U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001

SUBJECT: Grand Gulf Nuclear Station, Unit 1 Licensee Event Report 2022-001-00, Manual Reactor trip due to the loss of Balance of Plant Transformer 23

Grand Gulf Nuclear Station, Unit 1 Docket No. 50-416 Renewed License No. NPF-29

Attached is Licensee Event Report 2022-001-00, Manual Reactor trip due to the loss of Balance of Plant Transformer 23. This report is being submitted in accordance with 1 0 CFR 50.73(a)(2)(iv)(A) as an event or condition that resulted in manual or automatic actuation of the Reactor Protection System.

This letter contains no new Regulatory Commitments. Should you have any questions concerning the content of this letter, please contact Jeff Hardy, Regulatory Assurance Manager at 802-380-5124.

Sincerely,

JAH/saw

Attachments: Licensee Event Report 2022-001-00 G N RO2022-00028 Page 2 of 3

cc: NRC Senior Resident Inspector Grand Gulf Nuclear Station Port Gibson, MS 39150

U.S Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 GNRO2022-00028 Page 3 of 3

Attachment Licensee Event Report 2022-001-00 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 08/31/2023 Grand Gulf Nuclear Station, Unit 1 50-416 1 OF 3

. Title Manual Reactor trip due to the loss of Balance of Plant Transformer 23

5. Event Date 6. LEA Number 7. Report Date 8. Other Facilities Involved Sequential Rev Facility Name Docket Numbe Month Day Year Year Number No. Month Day Year N/A 05000 N/A 06 30 2022 2022 001 00 08 29 2022 Facility Name Docket Numbe N/A 05000 N/A

9. Operating Mode 10. Power Level 100 Precent

rt is Submitted Pursuantto the R uirements of 1 O CFR §: Check all that a I D 50.36(c)(2) ~ 50.73(a)(2)(iv)(A)

D 50.46(a)(3)(ii) D 50.73(a)(2)(v)(A) 0 20.2201 (d) 0 50.69(g) 0 50.73(a)(2)(v)(B) D 73.71 (a)(4)

D 20.2203(a)(1) 0 50.73(a)(2)(i)(A) 0 50.73(a)(2)(v)(C) D 73.71 (a)(s)

D 20.2203(a)(2)(i) 0 50.73(a)(2)(i)(B) D 50.73(a)(2)(v)(D) D 73.77(a)(1 )(i)

D 20.2203(a)(2)(ii) 0 50.73(a)(2)(i)(C) 0 50.73(a)(2)(vii) D 73.77(a)(2)(i)

D 20.2203(a)(2)(iii) 0 50.73(a)(2)(ii)(A) 0 50.73(a)(2)(viii)(A) D 73.77(a)(2)(ii)

D 20.2203(a)(2)(iv) 0 50.73(a)(2)(ii)(B) D 50.73(a)(2)(viii)(B)

D 20.2203(a)(2)(v) D 50.73(a)(2)(iii) 0 50.73(a)(2)(ix)(A)

D Other (Specify here, in Abstract, or in NRG 366A).

12. Licensee Contact for this LEA Licensee Contact Phone Number (Include Area Code)

Jeffery A. Hardy 802-380-5124

13. Com lele One Line for each Com nent Failure Described in this R Cause System Component Manufacturer Reportable To IRIS Cause System Component Manufacturer Reportable To IRIS C N/A N/A N/A y N/A N/A N/A N/A N/A

14. Supplemental Report Expected Month Day Year

~ D Yes (If No yes, complete 15. Expected Submission Date) 15. Expected Submission Date

Abstract

On June 30, 2022, at 1445 hours0.0167 days <br />0.401 hours <br />0.00239 weeks <br />5.498225e-4 months <br />, with the Grand Gulf Nuclear Station in MODE 1 and 100 percent power, the reactor was manually tripped due to the loss of balance of plant (BOP) transformer 23. All control rods fully inserted into the core and all systems responded appropriately. The plant was stabilized in MODE 3.

Standby Service Water A and B were manually initiated to supply cooling to the Control Room Air conditioning, Engineering Safety Feature (ESF) switchgear room coolers and plant auxiliary loads.

The direct cause of the BOP transformer 23 trip was an instantaneous ground overcurrent most likely caused by a lightning strike (environmental) flashover event.

There were no consequences to the safety of the public, nuclear safety, industrial safety, or radiological safety. No radiological releases occurred due to this event. This report is made in accordance with 10 CFR 50.73(a)(2)(iv)(A), for any event or condition that resulted in manual or automatic actuation of the Reactor Protection System (RPS).

DESCRIPTION OF EVENT

Prior to this event, the plant was at 100 precent power and Radial Well 3 was out of service. No activities were in progress that would have initiated the event. A thunderstorm was in the area.

On June 30, 2022, at 1441 hours0.0167 days <br />0.4 hours <br />0.00238 weeks <br />5.483005e-4 months <br />, balance of plant (BOP) transformer 23 feeder breaker tripped due to an instantaneous ground overcurrent lock out. This caused Radial Wells 4 and 5 to trip. Control Room received alarm indications on the instrument panel for 4.16kV BUS 28AG UNDERVOLTAGE and BOP XFMR 23 INCM FDR TRIP followed by several alarms on the Radial Well HMI and other control room panels as a result of feeder breaker tripping on ground overcurrent. After the loss of BOP transformer 23, the air release valves at Radial Well 6 lifted and diverted well output back to the caisson, resulting in the loss of all Plant Service Water (PSW) forward flow.

Standby Service Water A and B were manually initiated to supply cooling to the Control Room Air conditioning, Engineering Safety Feature (ESF) switchgear room coolers and plant auxiliary loads.

At 1443, Operations immediately entered loss of PSW procedure and lowered core flow to 70 Mlbm/hr in fast descent.

At 1445, operators placed the reactor mode switch into shutdown due to Turbine Building Cooling Water trends being unable to be maintained less than 100 degrees (and rising). During radial well recovery, E radial well pump (Radial Well 5) was able to be started remotely but the valves would not operate remotely, and F radial well pump would not start remotely.

REPORT ABILITY This report is made in accordance with 10 CFR 50. 73(a)(2)(iv)(A), for any event or condition that resulted in manual or automatic actuation of the Reactor Protection System (RPS).

CAUSE

The direct cause of the BOP transformer 23 trip was an instantaneous ground overcurrent most likely caused by a lightning strike (environmental) flashover event.

The direct cause was determined based on troubleshooting using the Failure Mode Analysis (FMA) and evaluation performed after the event in conjunction with a vendor and Entergy Distribution. It was found that there were several areas near the poles where lightning strikes had occurred, but that there was no evidence of a direct lightning strike on any of the poles or instrumentation.

CORRECTIVE ACTIONS

Completed actions to address the direct cause:

1. Initiated Operational Decision Making (ODM) to start plant up post-trip with all radial well loads powered from BOP 13 transformer.

2. Engineering performed post-event and post-maintenance walkdowns with a vendor and peer engineers to verify the readiness to re-energize the BOP 23 transformer.

3. Removed the wire mesh off all the BOP 23 Overhead Feeder Line poles and ensured that there were no stray ground wires running up above the neutral per Entergy Distribution recommendations.NRC FORM 366A (08-2020) U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 08/31/2023 Grand Gulf Nuclear Station, Unit 1 50-416 NUMBER NO.

2022 001 -00

Planned corrective actions

1. Develop Engineering Change to bury the BOP 23 Overhead Feeder Lines.

2. Implement Engineering Change to bury the BOP 23 Overhead Feeder Lines.

SAFETY SIGNIFICANCE

There were no safety consequences impacting plant or public safety as a result of this event. The reactor trip system responded as expected due to the manual trip signal received. There was no failure of any function that would have prevented fulfillment of actions necessary to shutdown the reactor and maintain it in a safe shutdown condition, remove residual heat, control the release of radioactive material, or mitigate the consequences of an accident. All systems required to bring the plant to MODE 3 responded correctly.

There was no loss of safety function for this event.

PREVIOUS SIMILAR EVENTS

CR-GGN-2021-5484: BOP 23 lightning strike. On July 15, 2021, at 1833 hours0.0212 days <br />0.509 hours <br />0.00303 weeks <br />6.974565e-4 months <br /> breaker 552-2103 tripped. This deenergized BOP 23 Transformer which was supplying Radial Wells 4 and 5 causing a loss of 4 Radial Well Pumps.

This resulted in a power reduction to 46 percent.

LER 2019-002: On May 12, 2019, at 10:39 hours the reactor was manually tripped due to a Significant Loss of PSW.

Reactor trip was due to loss of BOP 23 on hawk strike while Radial Well 3 out of service.