05000498/LER-2023-001, Pressurizer Power Operated Relief Valve Failed to Open

Pressurizer Power Operated Relief Valve Failed to Open

ML23163A248
Person / Time
Site:	South Texas
Issue date:	06/12/2023
From:	Harshaw K South Texas
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
NOC-AE-23003967, 35476883, G26 LER 2023-001-00
Download: ML23163A248 (1)

LER-2023-001, Pressurizer Power Operated Relief Valve Failed to Open

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), Loss of Safety Function
4982023001R00 - NRC Website

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Nuclear Operating Company South Texas f'roject Electric Generating Station f'O. Box 28:J Wadsworth, Texas 7748]

Attention: 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 2023-001-00 June 12, 2023 NOC-AE-23003967 10 CFR 50.73 STI: 35476883 File No. G26 Unit 1 Pressurizer Power Operated Valve Failed to Open Pursuant to reporting requirements of 10 CFR 50.73(a)(2)(i)(B) and 10 CFR 50.73(a)(2)(v)(D),

STP Nuclear Operating Company (STPNOC) hereby submits the attached South Texas Project (STP) Unit 1 Licensee Event Report (LER) 2023-001-00. Causal investigation is ongoing. Once completed, a supplement to this LER will be provided.

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 on this submittal, please contact Walter Fulton at 361-972-4349 or me at 361-972-4778.

Kimberly A. Harshaw Executive Vice President and Chief Nuclear Officer Attachment:

LER 2023-001-00, Unit 1 Pressurizer Power Operated Valve Failed to Open cc:

Regional Administrator, Region IV U.S. Nuclear Regulatory Commission 1600 E. Lamar Boulevard Arlington, TX 76011-4511

NOC-AE-23003967 Attachment Attachment LER 2023-001-00 Unit 1 Pressurizer Power Operated Valve Failed to Open

Abstract

On March 18, 2023, at 0933, during the shutdown of Unit 1 reactor for 1RE24, while in Mode 4 and performing surveillance procedure steps for Pressurizer Power Operated Relief Valve (PORV) PCV-0656A, the valve failed to open when the control room hand switch was taken to open. The surveillance was successfully re-performed later that shift and the valve was declared operable. The capability of the PORV to meet its design function for manual control of RCS pressure if it had been called upon to perform its safety functions during the time window from November 3, 2021, to March 18, 2023, was not assured. Therefore, PORV PCV-0656A was considered to have been inoperable during this time. On January 4, 2023, from 0757 until 1431, the PORVs could not have fulfilled their safety function for manual control of RCS pressure under postulated design basis conditions, because the second PORV PCV-0655A was unavailable due to scheduled maintenance on its power supply. The event was determined to be reportable per 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by Technical Specifications and per 10 CFR 50.73(a)(2)(v)(D) as a condition that could have prevented fulfillment of a safety function. The investigation into the cause of the failure is still in progress. A supplement to this LER will be submitted following completion of the investigation, which will identify cause(s) and follow up corrective actions.

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Summary of the Event Timeline (Note: All times Are Central Standard Time) 11/03/21 (1305) - Closed PZR PORV PCV-0656A Block Valve to determine if Pressurizer Safety Relief Valve HI temperature alarm was due to PZR PORV PCV-0656A seat leakage. Entered TS 3.4.9.3.

11/03/21 (1519) - Unit 1 entered Mode 3. TS 3.0.4.a was invoked for entering Mode 3 with PCV-0656A inoperable due to excessive seat leakage. Exited TS 3.4.9.3 and entered TS 3.4.4 Action (a) for PCV-0656A inoperable because of excessive seat leakage. The associated block valve remains closed with power on.

01/04/23 (0750) - Battery Bank E1A11 (power supply for PCV-0655A) declared inoperable and non-functional for planned maintenance.

01/04/23 (0950) - The Technical Specification 3.8.2.1.a Limiting Condition of Operation Action (a) and Technical Specification 3.8.3.1.h Action (e) for planned maintenance on Battery Bank E1A11 exceeded front stop completion time requiring entry into risk managed Technical Specifications.

01/04/23 (2345) - Declared ESF Battery E1A11 functional after being placed on 'float charge' with battery recharged.

03/17/23 (2251) - Unit 1 entered Mode 3 for 1RE24.

03/18/23 (0915) - Unit 1 entered Mode 4 for 1RE24. Entered Technical Specification 3.4.9.3 Action (c) for PCV-0656A inoperable. Technical Specification 3.4.4 for PCV-0656A is no longer applicable.

03/18/23 (0928) - Opened block valve for PCV-0656A. When opening block valve, PCV-0656A momentarily indicated an intermediate position.

03/18/23 (0933) - PCV-0656A failed to open during surveillance testing. Control board indication for Pressurizer PORV open command signal received at 0933:13.

03/18/23 (0937) - Control board indication for Pressurizer PORV open command signal cleared at 0937:10. Block Valve for PCV-0656A closed at 0937:22.

03/18/23 (0951) - PCV-0656A failed to stroke open during surveillance testing. The time of inoperability is tied to Mode 4 entry at 0915 on 03/18/2023. Remained in Technical Specification 3.4.9.3 Action (c).

03/18/23 (1218) - Opened block valve for PORV PCV-0656A to warm up lines for shutdown activities.

03/18/23 (1302) - Unit 1 entered Mode 5; entered Technical Specification 3.4.9.3 Action (d) for PCV-0656A inoperable and exited Technical Specification 3.4.9.3 Action (c).

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3. LER NUMBER YEAR SEQUENTIAL NUMBER REV NO.

052 050

III. Analysis of Event

A. Safety System Responses that Occurred No safety system responses occurred because of this event.

B. Duration of Safety System Inoperability

The capability of the PORV to meet its design function for manual control of RCS Pressure if it had been called upon to perform its safety functions during the time window from November 3, 2021, to March 18, 2023, is not assured.

C. Safety Consequences and Implications

The increase in risk due to the inoperability of PCV-0656A during the time period from November 3, 2021, to March 18, 2023, represents a very small change in risk. A maximum exposure time is limited to one year resulting in a delta-CDF or ICDP of 1.69E-07 and delta-LERF or ILERP of 1.06E-09. These results represent very small changes in risk per Regulatory Guide 1.174. For general transients, site-specific analysis demonstrates that bleed and feed success criteria requires 1 pressurizer PORV, a centrifugal charging pump (CCP) and 1 train of high head safety injection (HHSI) to mitigate the primary temperature and pressure increase for the bounding general transient case scenario of a Total Loss of Main Feedwater Flow event.

This 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 other safety-related equipment. Therefore, there was no adverse effect on the health and safety of the public.

IV. Cause of Event

Causal analysis is ongoing. Once the cause of the failure of PCV-0656A to open is determined, a supplement to this LER will be provided.

V. Corrective Actions

Causal analysis is ongoing. Once the cause of the failure of PCV-0656A to open is determined, corrective actions will be developed and a supplement to this LER will be provided.

VI. Previous Similar Events

A previous similar event, PCV-0656A failed to open during surveillance testing, this was identified entering outage 1RE23 on October 9, 2021, at 0833. The failure was determined to be a result of mechanical rubbing between the valve plug and cage assembly with the cage assembly measurements being out of tolerance. Corrective actions from the previous event included replacing the solenoid, plug, cage, and seat. (CR 21-10369) 5 5

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