05000499/LER-2024-002-01, Two Control Room Envelope HVAC Trains Inoperable Resulting in a Condition That Could Have Prevented Fulfillment of a Safety Function
| ML25132A132 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 05/12/2025 |
| From: | Tomlinson J South Texas |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| NOC-AE-25004101, 35729680 LER 2024-002-01 | |
| Download: ML25132A132 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 4992024002R01 - NRC Website | |
text
May 12, 2025 NOC-AE-25004101 10 CFR 50.73 STI: 35729680 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 2024-002-01 Supplement to Two Control Room Envelope HVAC Trains Inoperable Resulting in a Condition That Could Have Prevented Fulfillment of a Safety Function Reference: Letter; J. Tomlinson (STP) to Document Control Desk (NRC) - 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, October 17, 2024, (NOC-AE-24004073), (ML24291A284)
On October 17, 2024, STP Nuclear Operating Company (STPNOC) submitted the referenced Licensee Event Report. This letter is a supplement to the report to provide updates as a result of the causal investigation. The updated information is denoted by revision bars located in the right-hand margin. The report is submitted in accordance with 10 CFR 50.73.
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 2024-002-01, Supplement to 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 Tomlinson Digitally signed by Jason Tomlinson Date: 2025.05.12 11:17:59
- - 05'00'
NOC-AE-25004101 Attachment Attachment Unit 2 LER 2024-002-01 Unit 2 LER 2024-002-01, Supplement to Two Control Room Envelope HVAC Trains Inoperable Resulting in a Condition That Could Have Prevented Fulfillment of a Safety Function
Abstract
South Texas Project 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 01 05 12 2025 1
100%
Chris Warren, Licensing Engineer 361-972-7293 B
KM 23 B350 Y
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 the inability to control the chilled water temperature within the control band of 42 - 48 degrees Fahrenheit. 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. The Essential Chiller 22B Temperature Control Module (TCM) failed due to excessive equipment vibration conditions and age-related degradation of the electrolytic capacitors in the TCM panels. Corrective actions include implementation of design changes to relocate chiller control panels (including TCMs) to limit excitation vibration on the panels, establishment of a 5-year preventative maintenance action to replace Essential Chiller TCMs, and complete replacement of the previous-style TCMs in remaining Essential Chillers.
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 oscillating 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'.
2 5
South Texas Project Unit 2 00499 2024 002 01Page of
- 3. LER NUMBER YEAR SEQUENTIAL NUMBER REV NO.
052 050
VI. Previous Similar Events
The following Licensee Event Reports and supplements have been submitted due to Essential Chiller issues:
- 1. STP Unit 1 LER 2023-003-00, Two Essential Chilled Water Trains Inoperable Resulting in a Condition That Could Have Prevented Fulfillment of a Safety Function, January 09, 2024, (NOC-AE-24004007)(ML24009A282)
- 2. STP Unit 1 LER 2023-003-01 supplement, Two Essential Chilled Water Trains Inoperable Resulting in a Condition That Could Have Prevented Fulfillment of a Safety Function, June 19, 2024, (NOC-AE-24004048)(ML24171A011)
- 3. STP Unit 2 LER 2023-001-00, Two Essential Chilled Water Trains Inoperable Resulting in a Condition That Could Have Prevented Fulfillment of a Safety Function, January 15, 2024, (NOC-AE-24004005)(ML24015A002)
- 4. STP Unit 1 LER 2023-004-00, Condition Prohibited by Technical Specifications Due to Inoperable Train of Essential Chilled Water, February 05, 2024, (NOC-AE-24004012)(ML24036A352)
- 5. STP Unit 1 LER 2023-004-01 supplement, Condition Prohibited by Technical Specifications Due to Inoperable Train of Essential Chilled Water, April 25, 2024, (NOC-AE-24004030)(ML24116A317)
- 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 Project Unit 2 00499 2024 002 01