05000499/LER-2024-003, Containment Isolation Valve Inoperable Resulting in Condition Prohibited by Technical Specification and Prevention of Fulfillment of Safety Function

Containment Isolation Valve Inoperable Resulting in Condition Prohibited by Technical Specification and Prevention of Fulfillment of Safety Function

ML24296B226
Person / Time
Site:	South Texas
Issue date:	10/22/2024
From:	Tomlinson J South Texas
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
NOC-AE-24004074, STI: 35653612 LER 2024-003-00
Download: ML24296B226 (1)

LER-2024-003, Containment Isolation Valve Inoperable Resulting in Condition Prohibited by Technical Specification and Prevention of Fulfillment of Safety Function

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(v), Loss of Safety Function
4992024003R00 - NRC Website

text

October 22, 2024 NOC-AE-24004074 10 CFR 50.73 STI: 35653612 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 2024-003-00 Containment Isolation Valve Inoperable Resulting in Condition Prohibited by Technical Specification and Prevention of Fulfillment of Safety Functions Pursuant to reporting requirements in 10 CFR 50.73(a)(2)(i)(B), 10 CFR 50.73(a)(2)(v)(B), and 10 CFR 50.73(a)(2)(v)(D), STP Nuclear Operating Company (STPNOC) hereby submits the attached South Texas Project (STP) Unit 2 Licensee Event Report 2024-003-00.

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 Zachary Dibbern at 361-972-4336 or me at 361-972-8945.

Jason R. Tomlinson Site Vice President Enclosure: Unit 2 LER 2024-003-00, Containment Isolation Valve Inoperable Resulting in Condition Prohibited by Technical Specification and Prevention of Fulfillment of Safety Functions 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: 2024.10.22 16:53:49 -05'00'

NOC-AE-24004074 Enclosure Enclosure Unit 2 LER 24-003-00 Unit 2 LER 2024-003-00, Containment Isolation Valve Inoperable Resulting in Condition Prohibited by Technical Specification and Prevention of Fulfillment of Safety Functions

Abstract

South Texas Unit 2 I

00499 6

Containment Isolation Valve Inoperable Resulting in Condition Prohibited by Technical Specification and Prevention of Fulfillment of Safety Functions 08 24 2024 2024 003 00 10 22 2024 1

100%







Zachary Dibbern, Licensing Engineer 361-972-4336 B

CC ISV R344 Yes



On July 24, 2024, at 0959 CDT a level alarm for the Unit 2 Reactor Containment Building Chilled Water Expansion Tank was received coincident with Component Cooling Water (CCW) lineup changes. On August 29, 2024, at 0820 CDT, Train 'C' CCW system was declared inoperable for planned maintenance on Containment Isolation Valve 2R202T-CC-0199. It was discovered that 2R202T-CC-0199 had stem-to-disk separation due to missing taper pins and had been inoperable for almost 39 days. The past inoperability resulted in multiple Technical Specification Limiting Conditions of Operations not being met and was determined to be reportable as a condition prohibited by Technical Specifications and as a condition that could have prevented fulfillment of a safety function. The missing taper pins were determined to be the result of the pins not being secured. Corrective and extent of condition actions include: (1) 2R202T-CC-0199 was repaired, (2) planned internal inspection of two similar valves.

, two trains of systems being out that supported Residual Heat Removal (RHR) heat exchanger and mitigating the consequences of an accident (Reactor Containment Fan Coolers (RCFCs)).

B. Plant Operating Conditions Prior to Event Prior to the event on August 24, 2024, 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 and That Contributed To the Event There were no inoperable Structures, Systems, or Components at the start of the event that contributed to the event.

D. Narrative Summary of the Event Timeline (Note: All times are Central Daylight Time) 07/24/24 (0959) - Received level alarm 22M1/D3 for Reactor Containment Building (RCB) Chilled Water Expansion Tank Level HI/LO and ICS point LD9606. [Later determined to be firm evidence that there was stem-to-disk separation.]

2 6

South Texas Unit 2 00499 2024 003 00 IPage of

3. LER NUMBER YEAR SEQUENTIAL NUMBER REV NO.

052 050 III. Analysis of Event A. Safety System Responses that Occurred No safety systems responses occurred because of this event.

B. Duration of Safety System Inoperability Train C of the CCW was determined to be inoperable from 09:59, July 24, 2024, to 09:22, September 1, 2024, when the CCW Train C was declared OPERABLE following repair. This was a total of 38 days, 23 hours2.662037e-4 days <br />0.00639 hours <br />3.80291e-5 weeks <br />8.7515e-6 months <br />, and 23 minutes.

C. Safety Consequences and Implications A risk evaluation was performed to estimate the Incremental Core Damage Probability (ICDP) associated with this event.

The calculated ICDP from the inoperability of Train 2C CCW was determined to be a very small change in risk and is of very low safety significance. The event did not result in any offsite release of radioactivity or increase of offsite dose rates and 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 Event The 2R202T-CC-0199 isolation valve of the Train C CCW showed no indications that the tapered pins, that are used to secure the valve stem to the disk, were ever secured through staking or tack welding. The valve had not received any internal work since installation during construction. Therefore, the tapered pins would have worked loose overtime, and then on July 24, 2024, when the hydraulic transient occurred, the pin(s) ejected, allowing stem-to-disk separation and inoperability of the isolation valve. It is considered likely that one pint had ejected prior to this event due to the unlikelihood of two pins working loose and ejecting simultaneously.

V. Corrective Actions On September 9, 2024, the containment isolation valve 2R202T-CC-0199 repair was complete, and the valve was declared OPERABLE. Extent of condition actions are scheduled to look at the state of tapered pins in the similar valves 1-MOV-0199 and 2-MOV-0137 which are from the same purchase order.

VI. Previous Similar Events There were no previous recent similar events identified.

VII. Attachment

1. Equipment History Timeline 6

6 South Texas Unit 2 00499 2024 003 00 I

LER 2024-003-00 Equipment History Timeline Start End Duration (dd:hh:mm)

Inoperable Equipment Applicable Technical Speci"cations (TS) 07/24/24 0959 09/01/24 0922 38:23:23 Train C ECCS TS 3.5.2, 3.5.6, 3.6.2.3, 3.6.3, 3.7.3 action a, TS 07/27/24 0111 07/27/24 0127 00:00:16 Train A ECCS TS 3.5.2 action a 07/27/24 0129 07/27/24 0144 00:00:15 Train B ECCS TS 3.5.2 action a 07/29/24 0200 08/02/24 0204 04:00:04 Train 2A ECW TS 3.5.2, TS 3.5.6, TS 3.6.2.3, TS 3.7.3 action a 08/05/24 0400 08/06/24 1047 01:06:47 Train 2B ECW TS 3.5.2, TS 3.5.6, TS 3.6.2.3, TS 3.7.3 action a 08/07/24 0400 08/07/24 1429 00:10:29 Train B ECCS TS 3.5.2 action a 08/08/24 2309 08/11/24 1631 02:17:22 Train B Sequencer TS 3.7.3, TS 3.5.2, TS 3.7.14, TS 3.6.2.3, TS 3.6.2.1 08/20/24 2010 08/22/24 1128 01:15:18 Train B ECW TS 3.7.14, TS 3.5.2 action a 08/23/24 0127 08/23/24 0247 00:01:20 Train A ECCS TS 3.5.2 action a 08/23/24 0248 08/23/24 0335 00:00:47 Train B ECCS TS 3.5.2 action a