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| Title = Two Control Room Envelope HVAC Trains Inoperable Resulting in a Condition That Could Have Prevented Fulfillment of a Safety Function
| Title = Two Control Room Envelope HVAC Trains Inoperable Resulting in a Condition That Could Have Prevented Fulfillment of a Safety Function
| Plant =  
| Plant =  
| Reporting criterion = 10 CFR 50.73(a)(2), 10 CFR 50.73(a)(2)(v), 10 CFR 50.73(a)(2)(v)
| Reporting criterion = 10 CFR 50.73(a)(2)(v)
| Power level =  
| Power level =  
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{{#Wiki_filter:October 17, 2024 NOC-AE-2400 4073 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 20 24-002 -00 Two Control Room Envelope HVAC Trains Inoperable Resulting in a Condition That Could Have Prevented Fulfillment of a Safety Function
{{#Wiki_filter: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.
 
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.
The event did not have an adverse effect on the health and safety of the public.
There are no commitments in this submittal.
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.
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'


Jason R. Tomlinson Site Vice President
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


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
=Abstract=
 
South Texas Unit 2
cc:
Regional Administrator, Region IV U.S. Nuclear Regulatory Commission 1600 E. Lamar Boulevard Arlington, TX 76011-4511
 
NOC-AE-24004073 Attachment


Attachment
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%


Unit 2 LER 2024-002-00
Chris Warren, Licensing Engineer 361-972-7293
 
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=
On August 20, 2024, at 0400 hours, 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.


12 18 2024 On August 20, 2024, at 0400 hours, 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.
A causal investigation is scheduled to determine the cause of the Train 'B' Essential Chiller unit inoperability and corrective actions.


==I. Description of the Reportable Event==
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 hours and in COLD SHUTDOWN within the following 30 hours.
==A. Reportable Event Classification==
This event is reportable pursuant to 10 CFR 50.73(a)(2)(v)(D) as an event or condition that could have prevented fulfillment of a safety function of structures or systems that are needed to mitigate the consequences of an accident. The Essential Chilled Water system provides cooling water to the safety-related Air Handler Unit (AHU) of the Control Room Envelope (CRE) HVAC during normal and accident conditions. Two of three CRE HVAC trains are necessary for meeting all safety function requirements in the event of a safety injection signal actuation. With only one of three CRE HVAC trains OPERABLE from 2010 on August 20, 2024, to 1134 on August 21, 2024, the CRE HVAC system may not have been able to satisfy all safety function requirements in the event of an accident.
 
==B. Plant Operating Conditions Prior to Event==
Prior to the event, Unit 2 was in Mode 1 at 100% power.
 
C. Status of Structures, Systems, and Components That Were Inoperable at the Start of the Event that Contributed to the Event
 
At the start of the event, Train 'C' CRE HVAC was inoperable for planned maintenance.
 
==D. Narrative 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 hours and in COLD SHUTDOWN within the following 30 hours.
 
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':
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 hours restore at least two systems to OPERABLE status, or be in at least HOT STANDBY within the next 6 hours and in COLD SHUTDOWN within the following 30 hours.
With two Control Room HVAC Makeup and Cleanup Filtration Systems inoperable, within 72 hours restore at least two systems to OPERABLE status, or be in at least HOT STANDBY within the next 6 hours and in COLD SHUTDOWN within the following 30 hours.
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 (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'.
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
==E. Method of Discovery==
South Texas Unit 2 00499 2024 002 00Page of
The event was self-revealing when Train 'B' Essential Chilled Water system was declared inoperable and resulted in the cascading effect of inoperability of the Train 'B' Control Room Envelope HVAC system.
: 3. LER NUMBER YEAR SEQUENTIAL NUMBER REV NO.
 
052 050
==II. Component Failures==
==A. Failure Mode, Mechanism, and Effects of Failed Components==
A casual investigation is scheduled. A supplement to this report will be provided detailing failure mode(s), mechanism(s),
and effects of failed component(s) upon completion of the investigation.
 
==B. Cause of Component Failure==
A casual investigation is scheduled. A supplement to this report will be provided detailing causes upon completion of the investigation.
 
==C. Systems or Secondary Functions That Were Affected by the Failure of Components with Multiple Functions==
The Essential Chilled Water system provides chilled water to the following safety-related Air Handling Units (AHUs):
:- Main supply in Electrical Auxiliary Building (EAB)
:- Control room envelope in the EAB
:- Electrical penetration space emergency AHUs in the EAB
:- Reactor makeup water pump cubicle in the Mechanical Auxiliary Building (MAB)
:- Boric acid transfer pump cubicle in the MAB
:- Essential chiller area in the MAB
:- Chemical and volume control system valve cubicles in the MAB
:- Spent fuel pool pump cubicle in the Fuel Handling Building (FHB)
:- Containment sump isolation valve cubicle in the FHB
:- Engineered safety features (ESF) pump cubicles in the FHB
 
==D. Failed Component Information==
A causal investigation is scheduled. A supplement to this report will be provided detailing failed component information upon completion of the investigation.
 
==III. Analysis of the Event==
A. Safety System Responses that Occurred
 
No safety systems responded to the event.
 
==B. Duration of the Safety System Inoperability==
Trains 'B' and 'C' CRE HVAC were both inoperable from 2010 on August 20, 2024, until 1134 on August 21, 2024, when Train 'C' CRE HVAC was declared OPERABLE following planned maintenance. This is a total of 15 hours and 24 minutes.
This duration was within the 72-hour Allowed Outage Time for TS 3.7.7, Action 'c'.
 
==C. Safety Consequences and Implications==
The increase in risk due to the inoperability of both Essential Chilled Water Train 'B' and CRE HVAC Train 'C' for the exposure time represents a very small change in risk and is of very low safety significance. This assessment evaluated the risk impact from the time Essential Chilled Water Train B was declared inoperable on August 8, 2024, at 2010 until the time the CRE HVAC Train 'C' was declared OPERABLE on August 21, 2024, at 1134. This resulted in Delta Core Damage Frequency of 7.4E-09 and Delta Large Early Release Frequency of 4.6E-10. These results are within Region III for very small changes in risk per Regulatory Guide 1.174.
 
==IV. Cause of the Event==
A casual investigation is scheduled. A supplement to this report will be provided detailing causes upon completion of the investigation.
 
==V. Corrective Actions==
A casual investigation is scheduled. A supplement to this report will be provided detailing corrective actions upon completion of the investigation.
 
==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)
: 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)
: 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
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Latest revision as of 11:09, 24 November 2024

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)
v • d • e


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
v • d • e

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'.

2 5

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

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