05200025/LER-2024-002, Manual Reactor Protection System and Automatic Safeguards Actuation Due to an Unexpected Change in Position of a Main Feedwater Pump Minimum Flow Control Valve

Manual Reactor Protection System and Automatic Safeguards Actuation Due to an Unexpected Change in Position of a Main Feedwater Pump Minimum Flow Control Valve

ML24250A052
Person / Time
Site:	Vogtle
Issue date:	09/05/2024
From:	Martino P Southern Nuclear Operating Co
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
NL-24-0324 LER 2024-002-00
Download: ML24250A052 (1)

LER-2024-002, Manual Reactor Protection System and Automatic Safeguards Actuation Due to an Unexpected Change in Position of a Main Feedwater Pump Minimum Flow Control Valve

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(A), System Actuation
0252024002R00 - NRC Website

text

3/4,., Southern Nuclear September 05, 2024 Patrick Martino Site Vice President, Vogtle Units 3 & 4 7825 River Road Waynesboro, Georgia 30830

{706) 848-6602 tel 10 CFR 50.73(a)(2)(iv)(A)

Docket No.:

52-025 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Southern Nuclear Operating Company Vogtle Electric Generating Plant (VEGP) - Unit 3 Licensee Event Report 2024-002-00 Manual Reactor Protection System and Automatic Safeguards Actuation Due to an Unexpected Change in Position of a Main Feedwater Pump Minimum Flow Control Valve Ladies and Gentlemen:

In accordance with the requirements of 10 CFR 50.73(a)(2)(iv)(A), Southern Nuclear Operating Company is submitting the enclosed Licensee Event Report for VEGP Unit 3.

This letter contains no regulatory commitments. If you have questions regarding the enclosed information, please contact Will Garrett at (706) 848-7154.

Respectfully submitted, Patrick A. Martino Site Vice President Vogtle Units 3 & 4 PAM/kjd/cbg Enclosure:

Unit 3 Licensee Event Report 2024-002-00 CC:

Regional Administrator, Region II VPO Project Manager Senior Resident Inspector - Vogtle Units 3 & 4 Director, Environmental Protection Division - State of Georgia

Vogtle Electric Generating Plant - Unit 3 Licensee Event Report 2024-002-00 Manual Reactor Protection System and Automatic Safeguards Actuation Due to an Unexpected Change in Position of a Main Feedwater Pump Minimum Flow Control Valve Enclosure Unit 3 Licensee Event Report 2024-002-00

Abstract

On July 08, 2024, at 2125 EDT, with Vogtle Electric Generating Plant (VEGP) Unit 3 in Mode 1 at 100 percent power, the reactor was manually tripped due to a main feedwater pump (MFWP) minimum flow control valve (FCV) failing to an open position, followed by an automatic safeguards actuation due to rapid cooldown of the primary system. The unit was stabilized with decay heat removed through the passive residual heat removal heat exchanger. The cause of the event was an unexpected change in the MFWP minimum FCV from closed to fully open due to foreign material inside the valve positioner.

The valve positioner was replaced and an initial extent of condition review performed. In addition, a design change was made to initiate an automatic rapid power reduction upon failure of a MFWP minimum FCV, which will reduce the impact on steam generator water levels and eliminate the associated need to trip the reactor.

This event is reportable under 10 CFR 50. 73(a)(2)(iv)(A) due to the manual actuation of the reactor protection system, and the automatic actuation of the emergency core cooling system. VEGP Units 1, 2 and 4 were unaffected by this event.

EVENT DESCRIPTION I

2. DOCKET NUMBER

3. LER NUMBER I

YEAR SEQUENTIAL REV 00025 I 2024 I NUMBER NO.

- I 002 1-G On July 08, 2024, at 2125 EDT with Vogtle Electric Generating Plant (VEGP) Unit 3 in Mode 1 at 100 percent power the reactor protection system (RPS) [EIIS: JC] was manually actuated, followed by an automatic safeguards actuation [EIIS:

JE]. The initiating event was a failure of a main feedwater pump (MFWP) minimum flow control valve (FCV) [EIIS: SJ/FCV]

from its normally closed position to a fully open position, which is its fail-safe position per design. The unexpected change in valve position caused a reduction in the feedwater flow to the steam generators (SG)[EIIS: SB/SG]. The operators attempted to manually close the MFWP minimum FCV from the main control room and observed no response. The reduced feedwater flow caused the water level in the SG to lower and fall below the administrative critical parameter limit to manually trip the reactor. Immediately following the manual reactor trip, the SG #2 wide range water level briefly dropped below the setpoint to automatically actuate the passive residual heat removal heat exchangers (PRHR) [EIIS: BP/HX}.

Actuation of PRHR caused a rapid cooldown of the reactor coolant. As a result, the reactor coolant temperature dropped below the setpoint to automatically actuate safeguards on low reactor coolant temperature.

EVENT CAUSE ANALYSIS The cause of the event was an unexpected change in the MFWP minimum FCV to its fail-safe position due to foreign material inside the valve positioner (Valtek model Logix 3200 MD).

SAFETY ASSESSMENT AND REPORTABILITY There were no safety consequences as a result of this event. The operators responded timely to stabilize the plant. Decay heat was removed by PRHR heat exchangers.

There were no safety-related structures, systems, or components that were inoperable at the beginning of the event that contributed to the event. This event is reportable per 10 CFR 50.73(a)(2)(iv)(A) due to manual actuation of the RPS and the automatic actuation of the emergency core cooling system. All safety systems functioned as expected as a result of the event. VEGP Units 1, 2, and 4 were unaffected by this event.

CORRECTIVE ACTIONS

• The failed MFWP minimum FCV positioner was replaced and an initial extent of condition review performed.

• A design change was made to initiate an automatic rapid power reduction upon failure of a MFWP minimum FCV, which will reduce the impact on steam generator water levels and eliminate the associated need to trip the reactor.

PREVIOUS SIMILAR EVENTS None Page 2

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