05000499/LER-2024-002, Two Control Room Envelope HVAC Trains Inoperable Resulting in a Condition That Could Have Prevented Fulfillment of a Safety Function

Two Control Room Envelope HVAC Trains Inoperable Resulting in a Condition That Could Have Prevented Fulfillment of a Safety Function

ML24291A284
Person / Time
Site:	South Texas
Issue date:	10/17/2024
From:	Tomlinson J South Texas
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
NOC-AE-24004073, 35651860, STI: 35651860 LER 2024-002-00
Download: ML24291A284 (1)

LER-2024-002, Two Control Room Envelope HVAC Trains 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
4992024002R00 - NRC Website

text

October 17, 2024 NOC-AE-24004073 10 CFR 50.73 STI: 35651860 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 South Texas Project Unit 2 Docket No. STN 50-499 Licensee Event Report 2024-002-00 Two Control Room Envelope HVAC Trains 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 2 Licensee Event Report 2024-002-00 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 2 LER 2024-002-00, Two Control Room Envelope HVAC Trains 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: 2024.10.17 15:34:35 -05'00'

NOC-AE-24004073 Attachment Attachment Unit 2 LER 2024-002-00 Unit 2 LER 2024-002-00, Two Control Room Envelope HVAC Trains Inoperable Resulting in a Condition That Could Have Prevented Fulfillment of a Safety Function

Abstract

South Texas Unit 2

00499 5

Two Control Room Envelope HVAC Trains Inoperable Resulting in a Condition That Could Have Prevented Fulfillment of a Safety Function 08 20 2024 2024 002 00 10 17 2024 1

100%

Chris Warren, Licensing Engineer 361-972-7293

12 18 2024 On August 20, 2024, at 0400 hours0.00463 days <br />0.111 hours <br />6.613757e-4 weeks <br />1.522e-4 months <br />, Train 'C' Control Room Envelope (CRE) HVAC system was declared inoperable for planned maintenance. On August 20, 2024, at 2010, Train 'B' Essential Chilled Water system was declared inoperable due to an unexpected material condition with the essential chiller unit. A cascading effect of the Train 'B' Essential Chilled Water system was the inoperability of the Train 'B' CRE HVAC system. This condition was determined to be reportable per 10 CFR 50.73(a)(2)(v)(D) as a 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.

A causal investigation is scheduled to determine the cause of the Train 'B' Essential Chiller unit inoperability and corrective actions.

Summary of the Event Timeline (Note: All times are in Central Daylight Time) 08/20/2024 (0400) - Declared Train 'C' Control Room Envelope HVAC inoperable and non-functional for planned maintenance. Entered Technical Specification (TS) 3.7.7, Action 'a': With one Control Room Makeup and Cleanup Filtration System inoperable for reasons other than Condition B or Condition E, within 7 days restore the inoperable system to OPERABLE status, 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 in COLD SHUTDOWN within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />.

08/20/2024 (2010) - Train 'B' Essential Chilled Water system declared inoperable and non-functional due to swinging chilled water outlet temperatures and pre-rotation vanes and hot gas bypass valves cycling. Entered TS 3.7.7, Action 'c':

With two Control Room HVAC Makeup and Cleanup Filtration Systems inoperable, within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> restore at least two systems to OPERABLE status, 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 in COLD SHUTDOWN within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />.

08/21/2024 (0134) - Completed NRC 8-hour Non-Emergency Notification under 10 CFR 50.72(b)(3)(v)(D) as a condition that could have prevented the fulfillment of a safety function of structures or systems that are needed to mitigate the consequences of an accident. NRC Form 361 was emailed, read, and discussed with the NRC. Event Notification time was 0134 EDT on 8/21/2024. Event notification EN 57279.

08/21/2024 (1134) - Declared Train 'C' Control Room Envelope HVAC OPERABLE after planned maintenance, completed work package reviews, surveillance testing, and post-maintenance testing. Exited TS 3.7.7, Action 'c'.

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South Texas Unit 2 00499 2024 002 00Page of

3. LER NUMBER YEAR SEQUENTIAL NUMBER REV NO.

052 050

6. STP Unit 1 LER 2024-002-00, Two Essential Chilled Water Trains Inoperable Resulting in a Condition That Could Have Prevented Fulfillment of a Safety Function, May 09, 2024, (NOC-AE-24004040)(ML24130A271)

7. STP Unit 1 LER 2024-002-01 supplement, Two Essential Chilled Water Trains Inoperable Resulting in a Condition That Could Have Prevented Fulfillment of a Safety Function, June 27, 2024, (NOC-AE-24004047)(ML24179A341) 5 5

South Texas Unit 2 00499 2024 002 00