05000254/LER-2025-002, Control Room Emergency Ventilation Air Conditioning System Inoperable Due to Logic Issue
| ML25086A216 | |
| Person / Time | |
|---|---|
| Site: | Quad Cities  |
| Issue date: | 03/27/2025 |
| From: | Hild D Constellation Operating Services, Exelon Generation Co |
| To: | Office of Nuclear Material Safety and Safeguards, Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| SVP-25-016 LER 2025-002-00 | |
| Download: ML25086A216 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 2542025002R00 - NRC Website | |
text
Constellation...
SVP-25-016 March 27, 2025 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555 Quad Cities Nuclear Power Station, Unit 1 and 2 Renewed Facility Operating License No. DPR-29 and DPR-30 NRC Docket No. 50-254 and 50-265 10 CFR 50.73
Subject:
Licensee Event Report 254/2025-002-00 "Control Room Emergency Ventilation Air Conditioning System Inoperable due to Logic Issue" Enclosed is Licensee Event Report 254/2025-002-00 "Control Room Emergency Ventilation Air Conditioning System Inoperable due to Logic Issue," for Quad Cities Nuclear Power Station, Units 1 and 2.
This report is being submitted in accordance with 10 CFR 50.73(a)(2)(v)(D) for any 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.
There are no regulatory commitments contained in this letter.
Should you have any questions concerning this report, please contact Conner Bealer at 779-231-6207.
Res~+tf)i)
Doug Hild Site Vice President Quad Cities Nuclear Power Station cc:
Regional Administrator-NRC Region Ill NRC Senior Resident Inspector - Quad Cities Nuclear Power Station
Abstract
On 01/26/2025 at 14:50, the Control Room Emergency Ventilation (CREV) Air Conditioning (AC) system was declared inoperable due to a trip of the Refrigeration Condensing Unit (RCU) feed breaker. Technical Specification (TS) 3. 7.5 Condition A was entered at that time. Control Room operators discovered that the indicating light for the RCU was not lit. An operator was dispatched and found that the feed breaker had tripped. After post maintenance testing of the breaker, TS 3.7.5 Condition A was exited on 02/07/2025 at 00:30.
Initial troubleshooting narrowed down to two potential causes which includes breaker failure and loose breaker wiring. The causal product identified a design vulnerability where a simultaneous failure of a pressure switch and time delay relay could also cause the issue. The first two causes were addressed by breaker inspection and overhaul. The final cause will be addressed by replacement of a time delay relay and low suction pressure switch.
This is being reported in accordance with 10 CFR 50. 73(a)(2)(v)(D), any 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.
PLANT AND SYSTEM IDENTIFICATION
- 2. DOCKET NUMBER YEAR 00254 2024 -
- 3. LE R NUMBER SEQUENTIAL NUMBER 002 REV NO.
00 General Electric - Boiling Water Reactor, 2957 Megawatts Thermal Rated Core Power Energy Industry Identification System (EIIS) codes are identified in the text as [XX].
EVENT IDENTIFICATION Control Room Emergency Ventilation Air Conditioning System Inoperable Due to a Logic Issue
A. CONDITION PRIOR TO EVENT
Unit: 1 Reactor Mode: 1 Event Date: January 26, 2025 Mode Name: Power Operation Event Time: 1450 hours0.0168 days <br />0.403 hours <br />0.0024 weeks <br />5.51725e-4 months <br /> CST Power Level: 91%
No systems, structures, or components that were inoperable at the start of the event contributed to the event.
B. DESCRIPTION OF EVENT
On January 26, 2025, at 14:50, Operations identified that there was no indicating light for the Control Room Emergency Ventilation (CREV)[VI] Refrigeration [RFU] Condensing Unit (RCU) 0-9400-102 on the Main Control Room (MCR)[NA] Panel 912-5. An operator was dispatched and found that local indications also showed the RCU to have no power and the breaker [BKR] in a tripped condition. The station entered Technical Specification (TS) 3.7.5 Condition A for an inoperable CREV Air Conditioning (AC) [ACU] system.
ENS Notification#57515 was made in accordance with 10 CFR 50.72(b)(3)(v)(D) for any 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 CREV RCU is known to start with a high inrush of current. This was previously attributed to a "double start" condition where it would start once and then within seconds start again. Between 2009 and 2012, numerous trips of the CREV RCU breaker occurred. To eliminate these events a modification was installed in 2009 to add a time delay relay to the low suction pressure switch. The modification was to eliminate/reduce the number of "double starts" on the compressor and reduce the breaker tripping. In addition, the breaker dial setting was changed in 2012 from 8.1 to 9.4 to provide additional margin in the breaker trip setting.
All these previous events and changes to the logic and breaker settings have made the system more robust over time. Between 2012 and 2020, and again after 2020, there were no CREV RCU breaker trip events.
Because the CREV AC system is a single train system, this report is submitted in accordance with the requirements of 10 CFR 50.73(a)(2)(v)(D), which requires the reporting of 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.
C. CAUSE OF EVENT
- 2. DOCKET NUMBER YEAR 00254 2024 -
- 3. LER NUMBER SEQUENTIAL NUMBER 002 REV NO.
00 Initial troubleshooting narrowed down to two potential causes which includes breaker failure and loose breaker wiring. The causal product identified a design vulnerability where a simultaneous failure of a pressure switch and time delay relay could also cause the issue. A simultaneous failure could have potentially allowed a high inrush starting current during one of the CREV RCU compressor pump down cycles. A pump down cycle happens approximately every four hours. During the pump down cycle the RCU compressor starts for a short period to pump any liquid refrigerant from the suction side of the compressor to prevent compressor damage.
The first two causes were addressed by breaker inspection and overhaul. The final cause will be addressed by replacement of a time delay relay [62] and low suction pressure switch [PS].
D. SAFETY ANALYSIS
System Design
The purpose of the Control Room Emergency Ventilation system is to maintain the proper air environment for instrumentation and personnel in the Main Control Room. The CREV AC system is a single train safety-related system that is designed to maintain design temperature in the Control Room Envelope (CRE) under post-accident conditions. The loss of CREV AC could impact the plant's ability to mitigate the consequences of an accident. The CREV RCU is a key component of the CREV AC system and is a Carrier reciprocating compressor with a capacity of 90 tons. The backup to the CREV system is the Train A Control Room HVAC system, which is a non-safety related system.
Per Updated Final Safety Analysis Report (UFSAR) Section 6.4, "Habitability Systems," the Control Room Heating, Ventilation and Air conditioning (HVAC) systems are capable of maintaining the control room atmosphere suitable for occupancy throughout the duration of a Design Basis Accident (OBA). The RCU provides cooling to support CREVs operation. The emergency operation of CREVs requires manual actions.
Safety Impact The safety significance of this event was minimal. The CREV system filtration capability was not lost, and control room temperature was maintained during this event. In addition, the non-safety related Train A Control Room HVAC system was available and operating throughout this event.
E. CORRECTIVE ACTIONS
Immediate: The breaker cubicle was inspected and overhauled.
Follow-up: The time delay relay and the low suction pressure switch will be replaced.
F. PREVIOUS OCCURENCES
- 2. DOCKET NUMBER YEAR 00254 2024 -
- 3. LER NUMBER SEQUENTIAL NUMBER 002 REV NO.
00 The station events database, LERs and IRIS were reviewed for similar events at Quad Cities Nuclear Power Station. This event was a CREV RCU power issue, which was caused by a logic issue.
LER (254/2020-001-00) Control Room Emergency Ventilation Air Conditioning System Inoperable Due to Incorrect Breaker Setting, 04/14/2020. The CREV RCU was declared inoperable when the electrical feed breaker to the RCU was found in a tripped condition. This event was cause by an incorrect breaker setting for the RCU feed breaker. The breaker setting was changed in 2012, however the guidance documents for the preventative maintenance tasks on the RCU feed breaker were not updated prior to the PM task completion in 2013.
G. COMPONENT FAILURE DATA
Failed Equipment: BREAKER, MCC; 480V Component Manufacturer: Cutler-Hammer/Eaton Component Model Number: KD3250 Component Part Number: N/A This event has been reported to IRIS. Page_4_ of _4_