05200025/LER-2023-003, Automatic Reactor Protection System Actuation During Startup Testing Due to Incorrect Turbine Control Valve Setting

Automatic Reactor Protection System Actuation During Startup Testing Due to Incorrect Turbine Control Valve Setting

ML23159A223
Person / Time
Site:	Vogtle
Issue date:	06/08/2023
From:	Martino P Southern Nuclear Operating Co
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
ND-23-0376 LER 2023-003-00
Download: ML23159A223 (1)

LER-2023-003, Automatic Reactor Protection System Actuation During Startup Testing Due to Incorrect Turbine Control Valve Setting

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)
0252023003R00 - NRC Website

text

A Southern Nuclear Patrick Martino 7825 River Road Site Vice President, Waynesboro, Georgia 30830 Vogtle Unit 3 706 848 6602 tel

June 8, 2023 ND-23-0376

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 2023-003-00 Automatic Reactor Protection System Actuation During Startup Testing Due to Incorrect Turbine Control Valve Setting

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, Qc:?~~

Patrick A. Martino Site Vice President, Unit 3

PAM/KJD/sfr

Enclosure: Unit 3 Licensee Event Report 2023-003-00

CC:

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

Licensee Event Report 2023-003-00

Automatic Reactor Protection System Actuation During Startup Testing Due to Incorrect Turbine Control Valve Setting

Enclosure

Unit 3 Licensee Event Report 2023-003-00

Abstract

On April 10, 2023, at 0048 EDT with Vogtle Electric Generating Plant (VEGP) Unit 3 in Mode 1 at 18 percent power, the reactor protection system was automatically actuated due to low reactor coolant flow while conducting main generator testing activities.

The operators responded timely by stabilizing the plant and removing decay heat by the steam generator power operated relief valves. The cause of the event was incorrect turbine control valve logic setting which resulted in inadequate turbine speed and generator voltage. The corrective action for this event adjusted the turbine control valve logic setting to open the valves sufficiently to maintain turbine speed and generator output voltage to support house loads during operation in island mode (with the generator disconnected from the grid and supplying unit auxiliary loads).

This event is reportable under 10 CFR 50.73(a)(2)(iv)(A) as a condition that resulted in automatic actuation of the reactor protection system, which tripped the reactor. VEGP Units 1, 2, and 4 were unaffected by this event.

EVENT DESCRIPTION

On April 10, 2023, at 0048 EDT with the Vogtle Electric Generating Plant (VEGP) Unit 3 in Mode 1 at 18 percent power, the Reactor Protection System (RPS) [EIIS: JC) was automatically actuated during main generator system [EIIS: EL] startup testing. While performing procedure 3-ZAS-MEM-002, "Main Generator Initial Synchronization Testing," with the main generator connected to the offsite power grid and supplying approximately 65 Megawatts (MW), the switchyard breakers

[EIIS: FK / BKR] ZBS-161750 and ZBS-161850 were opened to disconnect the main generator from the offsite power grid and place the generator into island mode (supplying unit auxiliary loads). Shortly after placing the main generator in island mode, the turbine control system [EIIS: JJ] was not able to automatically maintain speed at the required 1800 rpm. This caused a reduction of speed and output voltage from the main generator, which resulted in a reduction in the speed of the Reactor Coolant Pumps [EIIS: AB / P]. This caused reduction in the reactor coolant flowrate, which resulted in the automatic RPS actuation. There were no structures, systems, or components that were inoperable at the beginning of the event that contributed to the event. This event is reportable under 10 CFR 50.73(a)(2)(iv)(A) as a condition that resulted in automatic actuation of the RPS.

EVENT ANALYSIS

The cause of this event was an incorrect turbine control valve setting, which was not identified through oversight of legacy design. The turbine control valve high limit setting was not set to maintain house loads during island mode operation. The turbine control valve high limit setting was set at 7 percent, which was a default value for turbine speed control and was not sufficient to support island mode operation. The software was changed to increase the high limit setting from 7 to 25 percent to support island mode operation.

SAFETY ASSESSMENT

There were no safety consequences due to this event because the automatic actuation function of the RPS maintained the plant in a safe condition. The operators responded timely following the reactor trip by ensuring plant stability and decay heat was removed by steam generator power operated relief valves [EIIS: SB / PCV]. All safety systems functioned as expected as a result of the event. There were no equipment failures that contributed to the event. VEGP Units 1, 2, and 4 were unaffected by this event.

CORRECTIVE ACTIONS

The turbine control valve setting was corrected by a software design change to increase the setting from 7 to 25 percent.

PREVIOUS SIMILAR EVENTS

None