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

text

Nuclear Operating Company.......

S o uth Texas f'roj ect Electric Generating Statio n f'O. Box 2 8:J Wads worth, Texas 7748 ]

June 12, 2023 NOC-AE-23003967 10 CFR 50.73 STI: 35476883 File No. G26

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 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.

I.Description of Event

A.Reportable Event Classification

This event is reportable per 50.73(a)(2)(i)(B) as a condition prohibited by Technical Specification and per 50.73(a)(2)(v)(D) as a condition that could have prevented fulfillment of a safety function.

Reporting Criterion 50.73(a)(2)(i)(B) is Any operation or condition which was prohibited by the plants Technical Specifications except when : (1) The Technical Specification is administrative in nature; (2) The event consisted solely of a case of a late surveillance test where the oversight was corrected, the test was performed, and the equipment was found to be capable of performing its specified safety functions; or (3) The Technical Specification was revised prior to discovery of the event such that the operation or condition was no longer prohibited at the time of discovery of the event.

The Technical Specification action statement for an inoperable PORV due to excessive seat leakage allows continued operation with the associated block closed because manual operation of the PORV is still available. In contrast, the action statement for a PORV inoperable for reasons other than excessive seat leakage states: restore the PORV to OPERABLE status or close the associated block valve and remove power from the block valve; within the following 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> restore the PORV to OPERABLE status or be in 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 HOT SHUTDOWN within the following 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />. In this event, the plant operated throughout the entire duration of Cycle 24 with PCV-0656A most likely not capable of meeting design requirements. This period exceeds the 72-hour allowed outage time of Technical Specification 3.4.4 Limiting Condition for Operations Action (b) for a PORV inoperable due to causes other than excessive seat leakage. Therefore, this event is considered reportable per 50.73(a)(2)(i)(B) as a condition prohibited by Technical Specifications.

Reporting Criterion 50.73(a)(2)(v) is Any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to: (A) Shut down the reactor and maintain it in a safe shutdown condition; (B)

Remove residual heat; (C) Control the release of radioactive material; or (D) Mitigate the consequences of an accident.

Only one pressurizer PORV is required for RCS pressure control to reach safe shutdown or to mitigate the consequences of a steam generator tube rupture. Pressurizer PORV PCV-0655A never experienced excessive seat leakage during Cycle 24.Plant computer data and Unit 1 control room logs were reviewed for the duration of Cycle 24 to identify any periods when PCV-0655A was declared inoperable. From January 4, 2023, at 0 750 until January 5, 2023, at 0415, the 125 Volt DC Bus which is the power supply for PCV-0655A was inoperable for surveillance testing. On January 4, 2023, a performance discharge test was performed on the 125 Volt DC Bus in accordance surveillance procedures. During the surveillance, the 125 Volt DC Bus breaker was opened, leav ing the 125 Volt D C Bus powered by the battery chargers. Computer history shows the breaker was opened at 0757 and was closed at 1431 on January 4, 2023. During those six and a half hours, PORV PCV-0655A would not have power to actuate the Solenoid Operated Valve (SOV) to open the PORV if there was a loss of offsite power and either Standby Diesel Generator #11 or the 125 Volt DC Bus was not promptly restored. Because the safety related design function of the PORVs is manual RCS pressure control with a loss of offsite power, from 0757 until 1431 on January 4, 2023, the PORVs could not have fulfilled their safety function for manual control of RCS pressure.

B.Plant Operating Conditions Prior To Event

Prior to the event on March 18, 2023, Unit 1 was In Mode 4 at 0% power.

C. Status Of Structures, Systems, and Components That Were Inoperable At the Start of the Event and That Contributed To the Event

At the start of the event, PORV PCV-0656A was inoperable due to observed excessive seat leakage.

D. Narrative 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-0 656A seat leakage. Entered TS 3.4.9.3.

11/03/21 (1519) - Unit 1 entered Mode 3. TS 3.0.4.a was in voked f or enterin g Mode 3 with PCV-0656A inoperable d ue to excessive seat leakage. Exited T S 3.4.9.3 and entered TS 3.4.4 Action (a) f or P CV-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 Techni cal Specification 3.8.2.1.a Limiting Condition of Operation Action (a) and Technical Specification 3.8.3.1.h Action (e) f or 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).

03/18/23 (1400) - Recommenced surveillance test of PCV-0656A.

03/18/23 (1420) - PCV-0656A opened and closed successfully. Reactor Coolant System pressure changed from 365 psig to 359 psig.

03/18/23 (1432) - PCV-0656A opened and closed successfully from the Aux Shutdown Panel during surveillance testing.

03/18/23 (1500) - Completed PORV operability test satisfactorily.

03/30/23 (1336) - Maintenance craft discovered an opening orifice installed in the solenoid operated valve for PCV-0656A while performing a work order. This is the same solenoid operated valve assembly that was installed during 1RE23.

Therefore, the opening orifice was in place during the entire operating cycle 24 and when PCV-0656A was tested on 03/18/23.

E.Method of Discovery The failure of the Unit 1 Pressurizer Power Operated Relief Valve to open was self-revealing as it was discovered during surveillance testing.

II.Component Failures A.Failure Mode, Mechanism, and Effects of Failed Component

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.

B.Cause of Component or System Failure

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.

C.Systems or Secondary Functions That Were Affected by the Failure of Components with Multiple Functions

No additional systems or secondary functions were affected by this failure.

D.Failed Component Information

System: Reactor Coolant System {AB}

Component: Valve, Solenoid Pressure {PSV}

Manufacturer: Crosby Valve Div/Geosource Inc {C710}

Model: DS-C-67970-13

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)