05000498/LER-2024-003, Condition Prohibited by Technical Specifications and Potential Loss of Safety Function Due to Inoperable Low Head Safety Injection Pump

Condition Prohibited by Technical Specifications and Potential Loss of Safety Function Due to Inoperable Low Head Safety Injection Pump

ML24183A174
Person / Time
Site:	South Texas
Issue date:	07/01/2024
From:	Harshaw K South Texas
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
NOC-AE-24004046, STI 35608947 LER 2024-003-00
Download: ML24183A174 (1)

LER-2024-003, Condition Prohibited by Technical Specifications and Potential Loss of Safety Function Due to Inoperable Low Head Safety Injection Pump

Event date:
Report date:
4982024003R00 - NRC Website

text

July 1, 2024 NOC-AE-24004046 10 CFR 50.73 STI: 35608947 ATTN: 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 2024-003-00 Condition Prohibited by Technical Specifications and Potential Loss of Safety Function Due to Inoperable Low Head Safety Injection Pump

Pursuant to reporting requirements in 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 Unit 1 Licensee Event Report 2024-003-00 for a condition prohibited by Technical Specifications and 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) 972-4778.

Kimberly A. Harshaw Executive Vice President and Chief Nuclear Officer

Enclosure: Unit 1 LER 2024-003-00, Condition Prohibited by Technical Specifications and Potential Loss of Safety Function Due to Inoperable Low Head Safety Injection Pump

cc:

Regional Administrator, Region IV U.S. Nuclear Regulatory Commission 1600 E. Lamar Boulevard Arlington, TX 76011-4511 NOC-AE-24004046 Enclosure

ENCLOSURE

Unit 1 LER 2024-003-00

Condition Prohibited by Technical Specifications and Potential Loss of Safety Function Due to Inoperable Low Head Safety Injection Pump

A. Reportable Event Classification

This event is reportable pursuant to 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by Technical Specifications (TS) and 10 CFR 50.73(a)(2)(v)(D) as a condition that could have prevented fulfillment of a safety function.

TS 3.5.2 action statement "a" for an INOPERABLE Low Head Safety Injection (LHSI) pump allows continued operation for up to either 7 days if at least two High Head Safety Injection (HHSI) pumps, two LHSI pumps, associated Residual Heat Removal (RHR) heat exchangers, and required flow paths from the Refueling Water Storage Tank to the Reactor Coolant System (RCS) are OPERABLE. The LHSI pump must be returned to OPERABLE status after 7 days or apply the requirements of the Configuration Risk Management Program (CRMP). If neither action (i.e. pump restoration to OPERABLE or application of CRMP requirements) is completed, then the Unit must be in HOT STANDBY (Mode 3) 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 (Mode 4) withing the following 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.

TS 3.5.2 action statement "b" for less than two of the required Emergency Core Cooling System (ECCS) subsystems OPERABLE requires restoration of at least two ECCS subsystems to OPERABLE status within one hour or apply the requirements of CRMP. If neither action is completed, then the Unit must be in HOT STANDBY (Mode 3) 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 (Mode 4) withing 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 Unit operated from April 3, 2023 until April 21, 2024 with LHSI pump 1A INOPERABLE without entering TS 3.5.2 action statement "a" and TS 3.5.2 action statement "b" when a second train of ECCS was INOPERABLE for maintenance or surveillance testing. This exceeds the 7-day restoration time in action statement "a" and the 1-hour restoration time in action statement "b". The requirements of CRMP were not applied for either action statement.

The analyzed accidents in the STP Updated Final Safety Analysis Report (UFSAR) that rely on ECCS for reactor core cooling and criticality control assume one train of ECCS is unavailable during the accidents. During a design basis Loss of Cooling Accident (LOCA), one unaffected (i.e. OPERABLE) ECCS train delivers make-up water to the affected RCS train with the pipe break while the second unaffected ECCS train provides additional cooling capabilities to reactor core. There were several instances from April 3, 2023 until April 21, 2024 where less than the required number of ECCS trains were OPERABLE to mitigate the consequences of an accident.

B. Plant Operating Conditions Prior to Event

Prior to the event, Unit 1 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

At the time of discovery, there were no other structures, systems, or components that were INOPERABLE that contributed to the event.

D. Narrative Summary of the Event

Timeline (Note: All times listed are Central Daylight Time)

03/23/2023 (1404): Train 'A' ECCS (includes LHSI pump 1A) declared INOPERABLE for the 'A' Train work window during the Unit 1 refueling outage.

04/02/2023: LHSI Pump 1A did not start. Breaker was re-racked and pump successfully started on the next attempt.

04/03/2023: Hand switch for LHSI Pump 1A was replaced. During the Post Maintenance Test (PMT), the first attempt to start the pump was unsuccessful. Electrical maintenance observed the breaker (did not perform any manipulations) when a 2nd attempt to start the pump was successful. The breaker was not cycled between pump start attempts.

04/03/2023 (1131): Train 'A' work window for Unit 1 refueling outage closed. LHSI pump 1A remains INOPERABLE and is a restraint to entering Mode 4 (Hot Standby).

04/04/2023: Replacement breaker for LHSI Pump 1A was installed with successful PMT. The breaker installed has the unrestrained washer.

04/04/2023 (2317): Operations declared LHSI pump 1A OPERABLE.

04/21/2024: During performance of Residual Heat Removal System Valve Operability Test, LHSI PUMP 1A failed to start.

When hand switch was placed in the START position the green light momentarily flickered off and the red light never illuminated. The Train A LHSI, High Head Safety Injection (HHSI), Containment Spray System (CSS) pump cubicle and containment sump isolation valve cubicle cooler fans did not start. A brief thump was heard from the motor but no shaft rotation was observed. No protective devices appear to be actuated on SWGR E1A Cubicle 6.

04/22/2024: Electrical maintenance started performing breaker inspections and troubleshooting.

04/23/2024: Electrical maintenance continued troubleshooting activities. A loose wire for the hand switch red light tightened and the red bulb was replaced.

04/24/2024: Electrical maintenance identified the unrestrained washer on a support plate above the "A" phase vacuum interrupter. A picture is provided in the Attachment. The breaker was removed and a spare breaker was installed with a successful PMT.

04/25/2024 (0341): Operations declared LHSI pump 1A OPERABLE.

E. Method of Discovery

The event was self-revealing when the LHSI pump 1A would not start on April 21, 2024. The unrestrained washer was identified in the breaker on April 24, 2024. The vendor provided confirmation the washer was present when the breaker was shipped to STP.

II. Component Failures

A. Failure Mode, Mechanism, and Effects of the Failed Components

The failed component in this event was the Train 'A' LHSI pump 1A breaker due to an unrestrained washer, which was foreign material, in the breaker. The presence of the washer adversely impacted the seismic qualification of the breaker, though the washer did not physically affect the functionality of the breaker until one year following installation. Based on a fault tree performed by Engineering, the most likely cause of the breaker's failure to close was due to either mechanical binding or a failure of the breaker's closed position latch, both of which could have been caused by the presence of the unrestrained washer. The circuit to energize LHSI pump 1A was not completed due to the washer preventing the breaker from fully closing.

B. Cause of Component Failure

Based on a fault tree performed by Engineering, the most likely cause of the breaker's failure to close was due to either mechanical binding or a failure of the breaker's closed position latch, both of which could have been caused by the presence of the unrestrained washer. Engineering was able to refute any contact, relay, charging springs, motor, and manufacturing flaws that could have caused the breaker to not perform its design functions.

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

Train 'A' Emergency Core Cooling System was INOPERABLE due to the inoperability of LHSI pump 1A.

D. Failed Component Information

System: Residual Heat Removal/Low Pressure Safety Injection System { BP }

Component: Breaker { BKR }

Manufacturer: Siemens { S125 }

Model: { 5HKR-250-1200-58 }

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

LHSI Pump 1A was INOPERABLE from 2317 on April 4, 2023, until 0341 on April 25, 2024, when LHSI Pump 1A was declared OPERABLE. This was a total 386 days and 24 minutes.

C. Safety Consequences and Implications

The increase in risk due to the inoperability of LHSI Pump 1A for the condition identified represents a very small change in risk. This assessment considered LHSI Train A unavailable during a seismic initiating event for 04/03/23 to 04/02/24, the time the breaker with the foreign material was installed until the last successful start of the LHSI Pump 1A, and the unavailability for LHSI Train A for all initiators for 04/02/24 to 04/25/24, the time of the last successful LHSI Pump 1A start until the pump was declared operable following corrective maintenance. This resulted in a total Incremental Core Damage Probability of 2.1872E-07 and a total Incremental Large Early Release Probability of 2.5568E-11. These results are within Region III for very small changes in risk per Regulatory Guide 1.174.

IV. Cause of the Event

The cause of the event was determined to be an error by the vendor when the washer was introduced into the breaker prior to shipping to STP. The purchase order for the component did have a requirement for the vendor to provide components free of foreign material. STP procurement and quality control personnel performed procedurally-required foreign material inspections during receipt activities and did not see the foreign material. STP Electrical Maintenance personnel performed another foreign material inspection prior to installation and did not see the foreign material.

V. Corrective Actions

Completed:

1. Condition Report (CR) Action 24-4015-8: Perform Extent of Condition review on all 4.16kV safety related breakers procured under Purchase Order 264203.

Planned:

1. CR Action 24-4015-18: Perform a foreign material inspection of breaker A2PKSG0E1A9, Serial Number

1. R-3009529574A-002.

2. CR Action 24-4015-19: Perform a foreign material inspection of breaker A2PKSG0E1A10, Serial Number

1. R-3009529574A-001.

VI. Previous Similar Events

No previous similar events that could have precluded this event were identified.

Attachment:

Picture of LHSI Pump 1A Breaker with As-Found Unrestrained Washer Attachment Picture of LHSI Pump 1A Breaker with As-Found Unrestrained Washer