05000373/LER-2024-004-01, Emergency Diesel Generator Auto-Start and Load Due to Loss of System Auxiliary Transformer

Emergency Diesel Generator Auto-Start and Load Due to Loss of System Auxiliary Transformer

ML24235A178
Person / Time
Site:	LaSalle
Issue date:	08/22/2024
From:	Mcbreen D Constellation Energy Generation
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
RA-24-025 LER 2024-004-01
Download: ML24235A178 (1)

LER-2024-004, Emergency Diesel Generator Auto-Start and Load Due to Loss of System Auxiliary Transformer

Event date:
Report date:
3732024004R01 - NRC Website

text

LaSalle County Station 2601 North 21' 1 Road Constellation~ Marseilles, IL 61341 815-415-2000 Telephone

RA24-025 10 CFR 50.73

August 22, 2024

U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001

LaSalle County Station, Units 1 and 2 Renewed Facility Operating License Nos. NPF-11 and NPF-18 NRC Docket No. 50-373 and 50-374

Subject: Licensee Event Report 2024-004-01, Supplement to Emergency Diesel Generator Auto-Start and Load due to Loss of System Auxiliary Transformer

Licensee Event Report 2023-002-01, Supplement to Air Circuit Breaker (ACB)

Mechanically Operated Contacts (MOC) switch failed to actuate

In accordance with 10 CFR 50. 73(a)(2)(iv)(A), Constellation Energy Generation, LLC (CEG) is submitting Licensee Event Report (LER) Number 2024-004-01 for LaSalle County Station, Unit 1.

In accordance with 10 CFR 50. 73(a)(2)(i)(B), CEG is submitting LER Number 2023-002-01 for LaSalle County Station, Units 1 and 2 due to administrative changes.

There are no regulatory commitments contained in this letter.

Should you have any questions concerning this report, please contact Ms. Laura Ekern, Regulatory Assurance Manager, at (815) 415-2800.

Respectfully, e~i~

Deborah J McBreen Acting Plant Manager LaSalle County Station

Enclosure: Licensee Event Report 2024-004-01 Licensee Event Report 2023-002-01

cc: Regional Administrator - NRC Region Ill NRC Senior Resident Inspector - LaSalle County Station (04-02 -2024) Esfmalad bU'den per re,poose to comp~ will tlis manda1ory colection request 80 holn. Reportad lessons

Abstract

During operability surveillance testing of the Unit 2, Division 2 Unit Cross Tie Air Circuit Breaker (ACB 2424), the Unit 1, Division 2 Cross Tie (ACB 1424) failed to close. It was found that the contact from the Mechanically Operated Contacts (MOC) switch of ACB 1422 was not made up as is required for closing in ACB 1424. Troubleshooting identified a misaligned linkage to the ACB 1422 MOC switch, resulting in contacts not closing as required. This established firm evidence that a past inoperability condition existed since the breaker was last racked out of service during the Unit 1 refueling outage in 2022.

Failure of ACB 1422 MOC switch contacts results in inoperability of one of the two offsite power sources for Unit 2 Division 2 required by LCO 3.8.1 (AC Sources - Operating) and degraded voltage protection required by LCO 3.3.8.1 (Loss of Power Instrumentation). At the failure time of discovery, Unit 2 was in Mode 5, and LCO 3.8.1 was not in the mode of applicability and the unit cross-tie power source was not required for LCO 3.8.2 (AC sources -Shutdown). There were no reportability thresholds applicable to this issue at the time of the event, and there was no loss of safety function. The condition is reportable in accordance with 10 CFR 50.73(a)(2)(i)(B) for operation or condition prohibited by Technical Specifications.

The MOC switch linkage was adjusted and ACB 1422 was restored to operable.

Plant and System Identification

LaSalle County Station Unit 2 is a General Electric Boiling Water Reactor with 3546 Megawatts Thermal Rated Core Power. The affected system was the AC Power system. The affected component is ACB 1422, Unit 1 System Auxiliary Transformer Main Feed to Unit 1 Division 2 AC power, 142Y.

Condition Prior to Event

Unit(s): 1/2 Date: February 24, 2023 Time: 14:25 CST Reactor Mode(s): 1/5 Mode(s) Name: Power Operation/Refuel Power Level: 100 percent/0 percent

Description

On 2/24/2023, during performance of the operability surveillance testing of the Unit 2, Division 2 Air Circuit Breaker (ACB) 2424, the Unit 1, Division 2 Cross Tie ACB 1424 failed to close. It was identified that that contacts on the Unit 1 System Auxiliary Transformer (SAT) feed to Division 2, ACB 1422, MOC switch remained in the open position when they should have been closed. This resulted in the ACB 1422 closing permissive not being actuated and preventing closure of ACB 1424. Troubleshooting identified a misaligned linkage on the ACB 1422 MOC switch. This linkage misalignment occurred during the last time the breaker was racked out of service during the Unit 1 refueling outage in 2022. This established firm evidence that a past inoperability condition existed.

Cause

Troubleshooting identified a misaligned linkage for the ACB 1422 MOC switch which resulted in the MOC switch contacts remaining open when they should have been closed.

Reportability and Safety Analysis

ACB 1422 MOC switch linkage misalignment occurred during the last time the breaker was racked out of service during the Unit 1 refueling outage in 2022. This established firm evidence that a past inoperability condition existed. There were no reportability thresholds met for this issue at the time of the event, and there was no loss of safety function. The condition is reportable in accordance with 10 CFR 50.73(a)(2)(i)(B) for operation or condition prohibited by Technical Specifications.

Failure of ACB 1424 to close resulted in inoperability of one of the two offsite power sources for Unit 2 Division 2 required by LCO 3.8.1 (AC Sources - Operating). At the time of discovery Unit 2 was in Mode 5, and LCO 3.8.1 was not in the mode of applicability. Additionally, the unit cross-tie power source was not required for LCO 3.8.2 (AC sources -

Shutdown). The required offsite power source for Unit 1 was not impacted by this failure. The contacts on ACB 1422 MOC switch also provide the permissive to enable degraded voltage protection for Unit 1 Division 2 emergency AC Power, 142Y. This function is required per LCO 3.3.8.1, (Loss of Power (LOP) Instrumentation).

LCO 3.8.1 requires two qualified circuits between the offsite transmission network and the onsite Class 1 E AC Electric Power Distribution System in modes 1, 2 and 3. Condition A is entered when one required offsite circuit is inoperable. The 1422 MOC switch contact remaining open prevents the closure of ACB 1424, Unit 1 SAT feed to Unit 2 Division 2 Emergency AC bus 242Y. As such one of the qualified offsite sources for bus 242Y was inoperable. The applicable Required Actions (RA) are RA A.1 perform SR 3.8.1.1 for operable required offsite circuit and A.3 restore the required offsite circuit to operable status in 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. If this action is not met Condition H is entered and requires the unit to be in Mode 3 in 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />.

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LCO 3.8.1 condition E is entered when one required offsite circuit AND one required Division 1, 2 or 3 Diesel Generator (DG) is inoperable. Required actions E.1 and E.2 include restore the required offsite circuit to operable OR restore the required DG to operable within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> or in accordance with the Risk Informed Completion Time Program. If this action is not met condition H is entered and requires the unit to be in Mode 3 within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. Examples of concurrent inoperability were identified where the required actions were not taken.

LCO 3.3.8.1 requires the Division 1, 2 and opposite Unit Division 2 - 4.16 kV Emergency Bus Undervoltage function to be operable (Function 1.c). If this function is inoperable LCO 3.3.8.1 condition A is entered and RA A.1 requires the channel to be placed in trip within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> or in accordance with the Risk Informed Completion Time Program. If this action is not met, condition 8.1 is entered and requires the associated DG to be declared inoperable immediately. The ACB 1422 linkage misalignment resulted in the Unit 2 Division 2 degraded voltage function to be inoperable when the Emergency Bus 142Y is fed from the System Auxiliary Transformer (SAT) and non-Emergency bus, 142X, is fed from the Unit Auxiliary Transformer (UAT). This lineup was entered during the period of inoperability with required actions not taken.

Corrective Actions

The linkage was adjusted and surveillance testing was completed to restore operability.

Previous Occurrences

No previous occurrences identified.

Component Failure Data

Manufacturer: ITE Device: Air Circuit Breaker, 4160V Component ID: 1AP06E-1, Air Circuit Breaker, System Auxiliary Transformer Main Feed to bus 142Y