05000498/LER-2024-001, Re Two Steam Generator Power Operated Relief Valves (Porvs) Inoperable Resulting in a Condition That Could Have Prevented Fulfillment of a Safety Function

Re Two Steam Generator Power Operated Relief Valves (Porvs) Inoperable Resulting in a Condition That Could Have Prevented Fulfillment of a Safety Function

ML24092A190
Person / Time
Site:	South Texas
Issue date:	04/01/2024
From:	Tomlinson J South Texas
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
NOC-AE-24004026, 35572977 LER-2024-001-00
Download: ML24092A190 (1)

LER-2024-001, Re Two Steam Generator Power Operated Relief Valves (Porvs) Inoperable Resulting in a Condition That Could Have Prevented Fulfillment of a Safety Function

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(v), Loss of Safety Function
4982024001R00 - NRC Website

text

April 1, 2024 NOC-AE-24004026 10 CFR 50.73 STI: 35572977 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 South Texas Project Unit 1 Docket No. STN 50-498 Licensee Event Report 2024-001-00 Two Steam Generator Power Operated Relief Valves (PORVs) Inoperable Resulting in a Condition That Could Have Prevented Fulfillment of a Safety Function Pursuant to reporting requirements in 10 CFR 50.73(a)(2)(v)(D), STP Nuclear Operating Company (STPNOC) hereby submits the attached South Texas Project Unit 1 Licensee Event Report 2024-001-00 for an 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.

The event did not have an adverse effect on the health and safety of the public.

There are no commitments in this submittal.

If there are any questions regarding this submittal, please contact Chris Warren at (361) 972-7293 or me at (361) 972-8945.

Jason R. Tomlinson Site Vice President Attachment: Unit 1 LER 2024-001-00, Two Steam Generator Power Operated Relief Valves (PORVs) Inoperable Resulting in a Condition That Could Have Prevented Fulfillment of a Safety Function cc:

Regional Administrator, Region IV U.S. Nuclear Regulatory Commission 1600 E. Lamar Boulevard Arlington, TX 76011-4511 Jason R Tomlinson Digitally signed by Jason R Tomlinson Date: 2024.04.01 08:05:01 -05'00'

NOC-AE-24004026 Attachment Attachment Unit 1 LER 24-001-00 Two Steam Generator Power Operated Relief Valves (PORVs) Inoperable Resulting in a Condition That Could Have Prevented Fulfillment of a Safety Function

Abstract

South Texas Unit 1

00498 5

Two Steam Generator Power Operated Relief Valves (PORVs) Inoperable Resulting in a Condition That Could Have Prevented Fulfillment of a Safety Function 01 23 2024 2024 001 00 04 01 2024 N/A N/A N/A N/A 3

0

Chris Warren, Licensing Engineer 361-972-7293 X

SB FU Gould S Yes B

SB AMP P095 Yes

On January 22, 2024, while in Mode 3, South Texas Project (STP) Unit 1 Steam Generator (S/G) 1A Power-Operated Relief Valve (PORV) was declared INOPERABLE. On January 23, 2024, while in Mode 3, STP Unit 1 S/G 1C PORV was declared INOPERABLE. This resulted in the inoperability of two of four S/G PORVs for approximately three hours until S/G 1A PORV was declared OPERABLE following corrective maintenance. In certain accident scenarios, the most limiting scenario being a Steam Generator Tube Rupture, more than two PORVs are needed to mitigate the consequences of an accident; therefore, this condition was determined to be reportable under 10 CFR 50.73(a)(2)(v)(D).

The S/G 1A PORV inoperability was caused by a blown fuse in the circuit that powers the servo amplifier board and the S/G 1C PORV inoperability was caused by a faulty servo amplifier board.

Completed corrective actions include corrective maintenance to replace a blown fuse to restore S/G 1A PORV to OPERABLE status on January 23, 2024, and corrective maintenance to replace the faulty servo amplifier board to restore S/G 1C PORV to OPERABLE status on January 24, 2024.

Summary of the Event Timeline (Note: All times are Central Standard Time) 01/22/24 (1025) - Operations declared Unit 1 Steam Generator PORV 1A INOPERABLE and Non-Functional due to failure to operate in AUTO or MANUAL. Entered Technical Specification (TS) 3.7.1.6 Action a: With one less than the required atmospheric steam relief valves OPERABLE, restored the required atmospheric steam relief valves to OPERABLE status within 7 days or apply the Configuration Risk Management Program (CRMP); or be in at least HOT STANDBY within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and place the required RCS / Residual Heat Removal (RHR) loops in operation for decay heat removal. Reactor trip breakers are open and loops "B", "C", and "D" are in operation with the steam generators as a heat sink.

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3. LER NUMBER YEAR SEQUENTIAL NUMBER REV NO.

052 050 C. Safety Consequences and Implications STP analyzed the Incremental Core Damage Probability and Incremental Large Early Release Probability for this event and concluded they are well below the non-risk significant threshold as defined by STP's Configuration Risk Management Program. This event was determined to be of very low safety significance based on the analysis performed.

The event did not result in any offsite release of radioactivity or increase in offsite dose rates. There were no personnel injuries or damage to any other safety-related equipment associated with this event.

Therefore, there was no adverse effect on the health and safety of the public.

IV. Cause of the Event The cause of the event was determined to be a blown fuse in Circuit 17 for panel DP1201 for S/G 1A PORV and an intermittent condition with S/G 1C PORV servo amplifier board that caused the fuse on the board to blow under normal electrical load.

V. Corrective Actions Completed:

1. Corrective maintenance to replace a blown fuse in Circuit 17 for panel DP1201 for S/G 1A PORV.

2. Corrective maintenance to replace a blown fuse and the servo amplifier board for S/G 1C PORV.

Planned:

No additional corrective actions are planned.

VI. Previous Similar Events The review of external Operating Experience did not identify any opportunities to identify this event prior to its occurrence.

A review of STP Condition Report Work Orders for all S/G PORVs did not identify any previous occurrences discussed in this LER within the last six years that would have helped identify any generic or underlying root causes that contributed to this event. The most recent servo amplifier board failure was in 2017 but was due to water intrusion into the component.

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