05000373/LER-2023-001, Low Pressure Core Spray Inoperable Due to Minimum Flow Valve Flow Pressure Switch Failure

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Low Pressure Core Spray Inoperable Due to Minimum Flow Valve Flow Pressure Switch Failure
ML23167A071
Person / Time
Site: LaSalle 
Issue date: 06/16/2023
From: Casey Smith
Constellation Energy Generation
To:
Office of Nuclear Reactor Regulation, Document Control Desk
References
RA23-031 LER 2023-001-00
Download: ML23167A071 (1)
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LER-2023-001, Low Pressure Core Spray Inoperable Due to Minimum Flow Valve Flow Pressure Switch Failure
Event date:
Report date:
Reporting criterion: 10 CFR 50.73(a)(2)(v), Loss of Safety Function
3732023001R00 - NRC Website
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text

Constellation~

RA23-031 June 16, 2023 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001

.*.~*,

,u..***aaL, LaSalle County Station, 1 Renewed Facility Operating License No. NPF-11 NRC Docket No. 50-373 LaSalle County Station 2601 North 21 " Road Marseilles. IL 61341 815-415-2000 Telephone 10 CFR 50.73

Subject:

Licensee Event Report 2023-001-00, Low Pressure Core Spray Inoperable due to Minimum Flow Valve Flow Pressure Switch Failure In accordance with 10 CFR 50.73(a)(2)(v)(D), Constellation Energy Generation, LLC (CEG) is submitting Licensee Event Report (LER) Number 2023-001-00 for LaSalle County Station, Unit 1.

There are no regulatory commitments in this letter. Should you have any questions concerning this report, please contact Mr. Dan Mearhoff, Regulatory Assurance Manager, at (815) 415-2800.

Respectfully, Christopher Smith Plant Manager LaSalle County Station

Enclosure:

Licensee Event Report cc:

Regional Administrator - NRC Region Ill NRC Senior Resident Inspector-LaSalle County Station

Abstract

During station surveillance testing, the Low Pressure Core Spray (LPCS) pump discharge flow differential pressure switch malfunctioned, preventing the LPCS pump minimum flow valve from opening on a low flow condition. As a result the LPCS pump was declared inoperable. The cause of the differential pressure switch failure was water leakage into the switch electrical housing caused by a failure of the shaft seal. The faulty switch was replaced and the LPCS pump was restored to operable status.

This condition could have prevented the LPCS system from performing its safety function. This condition is reportable in accordance with 10 CFR 50. 73(a)(2)(v)(D) as an event or condition that could have prevented fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident. There were minimal safety consequences associated with the condition since other emergency safety systems remained operable.

2. DOCKET NUMBER
3. LER NUMBER SEQUENTIAL REV YEAR NUMBER NO.

373 2023 -

01 00 LaSalle County Station Unit 1 is a General Electric Boiling Water Reactor with 3546 Megawatts Thermal Rated Core Power.

The Low Pressure Core Spray (LPCS) system is part of the Division 1 Emergency Core Cooling System (ECCS). LPCS provides low-pressure coolant into the reactor core under accident conditions. The LPCS minimum flow switch, 1 E21-N004, monitors pump discharge flow. This flow switch initiates opening and closing the of LPCS minimum flow valve, 1E21-F011.

Condition Prior to Event

Unit(s): 1 Reactor Mode(s): 1

Description

Date: April 17, 2023 Mode(s) Name: Power Operation Time: 0246 CDT Power Level: 100%

At 0246 CDT on April 17, 2023, it was discovered that the single train Low Pressure Core Spray (LPCS) system was inoperable. To support Reactor Core Isolation Cooling (RCIC) surveillance testing, the LPCS pump was started for suppression pool mixing. When attempting to secure the LPCS pump, the LPCS minimum flow valve did not open on low flow as expected. It was identified that the pump discharge flow differential pressure switch had failed causing the minimum flow valve to not perform its design function. This resulted in inoperability of the LPCS pump. LPCS was declared inoperable and the appropriate Technical Specification (TS) required actions were entered in accordance with TS 3.5.1, "ECCS - Operating" and TS 3.3.5.1, "Emergency Core Cooling System (ECCS) Instrumentation."

Cause

The cause of the switch failure is process water intrusion into the switch electrical housing. The water intrusion was caused by a failure of the low pressure side u-cup seal around the shaft from the sensing element.

Reportability and Safety Analysis

There were minimal safety consequences associated with the condition since other emergency safety systems remained operable during the period of LPCS inoperability.

This event is reportable in accordance with 10 CFR 50.73(a)(2)(v)(D) as an event or condition that condition that could have prevented fulfillment of a safety function of structures or systems that are needed to mitigate the consequences of an accident. An 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> ENS report was made to the NRC at 0937 EDT on April 17, 2023 (EN 56471 ).

Safety System Functional Failure Review The condition is a safety system functional failure (SSFF) defined in accordance with NEI 99-02, Regulatory Assessment Performance Indicator Guidance. The failure of the 1 E21-N004 switch caused the minimum flow valve to not open when required.

Corrective Actions

2. DOCKET NUMBER YEAR 373 2023
3. LER NUMBER SEQUENTIAL NUMBER 01 REV NO.

00 The failed differential pressure switch was replaced and LPCS was returned to operable status.

Actions created to evaluate extent of condition, parts reliability and design changes.

Previous Occurrences

LER 373-2017-006-00 Low Pressure Core Spray Inoperable due to Minimum Flow Valve Failure in Closed Position On May 17, 2017, the Unit 1 LPCS minimum flow valve unexpectedly closed when the pump was in standby. The closure was due to a failed SOR differential pressure switch (Model 141 N6-WX7-M9-C1A-JJTTNQ). Water intrusion into the switch electrical housing for the minimum flow switch, 1 E21-N004, resulted in a ground fault causing the actuation of logic and subsequent LPCS minimum flow valve closure. The cause was determined to be process water leakage past an internal "U-cup" seal around the shaft from the sensing element into the electrical switch housing.

Component failure data

Manufacturer: Static O-Ring SOR Inc. (S382)

Device (Model): Differential Pressure Switch (141 N6-WX7-M9-C1A-JJTTNQ)

Component ID: LPCS Pump Discharge Flow Bypass Interlock (1 E21-N004) Page_3_ of _3_

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