05000416/LER-2024-001, High Pressure Core Spray Inoperable Due to Minimum Flow Valve Failure to Close

High Pressure Core Spray Inoperable Due to Minimum Flow Valve Failure to Close

ML24087A196
Person / Time
Site:	Grand Gulf
Issue date:	03/27/2024
From:	Hardy J Entergy Operations
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
GNRO2024-00011 LER 2024-001-00
Download: ML24087A196 (1)

LER-2024-001, High Pressure Core Spray Inoperable Due to Minimum Flow Valve Failure to Close

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(v), Loss of Safety Function
4162024001R00 - NRC Website

text

Entergy O perations, Inc.

S} entergy P.O. Box 756 Port G ibson, Mississippi 39150

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

10 CFR 50.73

GNRO2024-00011

March 27, 2024

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

SUBJECT: Grand Gulf Nuclear Station, Unit 1 Licensee Event Report 2024-001-00, High Pressure Core Spray Inoperable due to Minimum Flow Valve Failure to Close

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

Attached is Licensee Event Report (LER) 2024-001-00, High Pressure Core Spray Inoperable due to Minimum Flow Valve Failure to Close. This report is being submitted in accordance with 10 CFR 50.73(a)(2)(v)(D), any event or condition that could have prevented the fulfillment of the safety function of systems that are needed to mitigate the consequences of an accident.

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

Sincerely,

Digitally signed by Jeff Hardy DN: cn=Jeff Hardy, c=US, Jeff Hardy email=jhardy@entergy.com Date: 2024.03.27 13:09:43 -

05'00' JAH/saw

Attachments: Licensee Event Report 2024-001-00 GNRO2024-00011 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 GNRO2024-00011 Page 3 of 3

Attachment Licensee Event Report 2024-001-00

Abstract

On January 29, 2024, Grand Gulf Nuclear Station was operating at 100 percent power, and all safety systems were operable. At 1005 CT, during surveillance testing of the High Pressure Core Spray (HPCS) system, the HPCS minimum flow valve went from full open indication to dual indication and failed to close as expected. The cause of the valve's failure to close was a sheared actuator motor pinion key. The actuator motor pinion key was replaced using updated work instructions.

Although HPCS was declared inoperable during the event, an engineering evaluation concluded that HPCS system remained able to perform its safety functions to maintain thermal limits and address pressurized and depressurized conditions in the reactor pressure vessel. Therefore, there were no actual safety consequences to the event.

This report is being made in accordance with 10 CFR 50.73(a)(2)(v)(D), for any event or condition that could have prevented the fulfillment of the safety function of systems that are needed to mitigate the consequences of an accident.

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

DESCRIPTION

On January 29, 2024, Grand Gulf Nuclear Station (GGNS) was operating at 100 percent power, and all safety systems were operable. At 0950 CT, the site began Technical Specification 3.5.1, ECCS Operating surveillance testing on the High Pressure Core Spray (HPCS) [BG] system. At 1005 CT, during the surveillance, HPCS minimum flow valve went from full open indication to dual indication and failed to close as expected. At 1620 CT, the HPCS minimum flow valve was manually closed.

REPORT ABILITY The HPCS minimum flow valve failure to close was initially reported to the NRC as an 8-hour report per 10 CFR 50.72(b)

(3)(v)(D) on January 29, 2024 (EN 56938). This report is made in accordance with 10 CFR 50.73(a)(2)(v)(D) for any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident.

Although HPCS was declared inoperable during the event, an engineering evaluation concluded that HPCS system remained able to perform its safety functions to maintain thermal limits and address pressurized and depressurized conditions in the reactor pressure vessel. Therefore, in accordance with NEI 99-02, Regulatory Assessment Performance Indicator Guideline, Section 2.2, Mitigating Systems Cornerstone, Sub-Section, Safety System Functional Failures, this event will not be counted against the Reactor Oversight Process Safety System Functional Failure Performance Indicator.

CAUSE

Trouble shooting was initiated and it was determined that the actuator motor pinion key had sheared off preventing the valve from actuating. Further investigation determined that the pinion key had not been correctly staked due to inadequate procedure instructions when the actuator motor was replaced in 2010.

CORRECTIVE ACTIONS

Immediately following the event, the HPCS minimum flow valve was manually closed.

A new motor pinion key was installed using updated work instructions.

Extent of condition actions are being developed to inspect motor pinion keys on similar valves.

SAFETY SIGNIFICANCE

There were no actual safety consequences associated with the condition described in this report. The HPCS system provides and maintains an adequate coolant inventory inside the reactor vessel to limit the fuel cladding temperatures in the event of breaks in the reactor coolant pressure boundary. The system is initiated by either high pressure in the drywell or low water level in the reactor vessel. Though the as-found HPCS minimum flow valve position rendered the system inoperable throughout the time period, the HPCS system was able to perform its safety functions for maintaining thermal limits. The HPCS system was able to address pressurized as well as depressurized (LOCA) conditions in the reactor pressure vessel.

PREVIOUS SIMILAR EVENTS

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