05000254/LER-2025-004, Loss of Suppression Chamber Vacuum Breaker Safety Function Due to Configuration Control Error
| ML25155A098 | |
| Person / Time | |
|---|---|
| Site: | Quad Cities  |
| Issue date: | 06/04/2025 |
| From: | Hild D Constellation Energy Generation |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| SVP-25-031 LER 2025-004-00 | |
| Download: ML25155A098 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2542025004R00 - NRC Website | |
text
Constellation.
SVP-25-031 June 4, 2025 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555 Quad Cities Nuclear Power Station, Unit 1 Renewed Facility Operating License No. DPR-29 NRC Docket No. 50-254 10 CFR 50.73
Subject:
Licensee Event Report 254/2025-004-00 "Loss of Suppression Chamber Vacuum Breaker Safety Function due to Configuration Control Error
Enclosed is Licensee Event Report 254/2025-004-00 "Loss of Suppression Chamber Vacuum Breaker Safety Function due to Configuration Control Error".
This report is being submitted 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 systems needed to mitigate the consequences of an accident, and 10 CFR 50.73(a)(2)(i)(B), any operation or condition prohibited by Technical Specifications.
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.
RespJ~~
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 04/05/2025 at 04:00, Operations determined that a mispositioned manual isolation valve made both trains of Reactor Building to Suppression Chamber Vacuum Breakers simultaneously inoperable. The vacuum breaker inoperability could have prevented fulfillment of primary containment function following a design-basis accident with no operator intervention. The valve was not properly repositioned following refuel outage activities in March of 2025.
The cause of the valve mispositioning was inadequate standards in Procedure Use and Adherence during refuel outage activities. Immediate corrective action was to open the isolation valve. Subsequent actions will be to make the valve a locked-open valve, to improve related procedures, and to provide training related to this event.
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 systems needed to mitigate the consequences of an accident, and 1 O CFR 50.73(a)(2)(i)(B),
any operation or condition prohibited by Technical Specifications.
PLANT AND SYSTEM IDENTIFICATION
- 2. DOCKET NUMBER YEAR 00254 2025
- 3. LE R NUMBER SEQUENTIAL NUMBER 004 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 Loss of Suppression Chamber Vacuum Breaker Safety Function due to Configuration Control Error
A. CONDITION PRIOR TO EVENT
Unit: 1 Reactor Mode: 1 Event Date: May 5, 2025 Mode Name: Power Operation Event Time: 0400 hours0.00463 days <br />0.111 hours <br />6.613757e-4 weeks <br />1.522e-4 months <br /> CST Power Level: 100%
No systems, structures, or components that were inoperable at the start of the event contributed to the event.
B. DESCRIPTION OF EVENT
On 04/05/2025 at 04:00, Operations discovered that manual isolation valve [V] 1-1601-84B, U1 Torus Line 1-1635B-1/2 inch LA Root Valve, was in the closed position. Closure of the 1-1601-84B (-84B) valve prevents operation of air operated Reactor Building to Suppression Chamber Vacuum Breakers [VACB][BF] 1-1601-20A and 1-1601-20B, hereafter denoted as "the vacuum breakers." The -84B valve isolated differential pressure sensors [DPS] from the suppression pool atmosphere, subsequently preventing the operation of solenoid valves [PDSV] providing air to the vacuum breakers. Technical Specification {TS) 3.6.1.7, Reactor Building to Suppression Chamber Vacuum Breakers, Conditions C and E were entered for each vacuum breaker. Condition C is for one line with one or more reactor building to suppression chamber vacuum breakers inoperable for opening; Condition E is for two lines with one or more vacuum breakers inoperable for opening. The -84B valve was opened, and TS 3.6.1.7 was exited on 04/05/2025 at 0400. The vacuum breaker inoperability could have prevented fulfillment of primary containment function following a design-basis accident with no operator intervention. Additionally, the TS 3.6.1.7 Condition E Completion Time of 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> was not met based on the Required Action to restore vacuum breakers in one of two lines to operable status following entry into Mode 2. Also, TS Limiting Condition for Operation (LCO) 3.0.4 was not met when Mode 2 was entered without any specific allowances or risk assessments performed for the vacuum breaker inoperability related to TS 3.6.1.7.
During the refuel outage, March 10, 2025, through April 1, 2025, Local Leak Rate Tests (LLRTs) and valve maintenance activities included closure of the -84B valve. At the conclusion of the as-left LLRT on 03/28/25, steps to open the -84B and other valves were annotated that they were to be left closed per the Unit Supervisor, with a Senior Reactor Operator (SRO) having an expectation that subsequent outage clearance order activities would later recover the desired valve position. No peer reviews were performed on the incomplete steps, nor were any verifications made related to the applicable clearance order, resulting in the isolation valves remaining closed the duration of the refuel outage.
- 2. DOCKET NUMBER
- 3. LER NUMBER YEAR SEQUENTIAL REV NUMBER NO.
00254 2025 -
004 00 The valve remained closed through reaching the Mode of Applicability for TS 3.6.1.7, Mode 2, on 03/31/2025 at 1052, and through Mode 1 operation. In subsequent days, unexpected continuous operation of a compressor [CMP] associated with differential pressure control between the drywell and the suppression chamber resulted in troubleshooting of compressor control instruments. This is when the -84B valve was found closed. The -84B valve was opened on 04/05/2025 at 0400.
The total time the vacuum breakers were inoperable in the modes of applicability was 4 days, 17 hours1.967593e-4 days <br />0.00472 hours <br />2.810847e-5 weeks <br />6.4685e-6 months <br />, and 8 minutes. TS 3.6.1. 7 Condition C has a 7-day completion time, which was not exceeded. TS 3.6.1.7 Condition E has a 1-hour completion time, which was exceeded.
Event Notification System report 57647 was submitted on 04/05/2025 at 1133.
C. CAUSE OF EVENT
The cause of the self-identified event was inadequate standards in Procedure Use and Adherence.
The procedure step to recover the -84B has instructions to "perform system restoration as follows, or as directed by the Unit Supervisor." The SRO performing the LLRT procedure incorrectly assumed that the -84B would be restored through some other process but did not validate this assumption or obtain a peer check, as was required by procedure. Instead, the procedure step was annotated that the valve would be left closed per the Unit Supervisor.
A failure to properly reinforce the required Human Performance and Technical Human Performance standards contributed to this event.
D. SAFETY ANALYSIS
System Design
Automatic vacuum relief devices on the drywell and the suppression chamber prevent the primary containment from exceeding the design external-to-internal pressure differential. The drywell is designed for a maximum external pressure of 2 psi greater than the concurrent internal pressure. The suppression chamber is designed for a maximum external pressure of 2 psi greater than the concurrent internal pressure based on the original design calculations; however, the overpressure capability of the suppression chamber is conservatively stated to be 1.0 psi.
The suppression chamber vacuum breakers prevent excessive vacuum in the suppression chamber relative to the reactor building by admitting reactor building air at a preset pressure differential that does not exceed the equivalent of 0.5 psid. Two vacuum breaker valves in series are used in each of two lines leading from the reactor building atmosphere. One valve in each line (vacuum breakers 1-1601-20A or -20B) is air-operated and actuated by a differential pressure signal, independently of electrical power. The second valve in each
- 2. DOCKET NUMBER
- 3. LER NUMBER YEAR SEQUENTIAL REV NUMBER NO.
00254 2025 -
004 00 line is self-actuating. The combined pressure drop at rated flow through both valves does not exceed the difference between suppression chamber design external pressure and maximum atmospheric pressure.
Safety Impact There were no safety consequences as a result of this event. There was no radiation release associated with this event. Operations took immediate actions upon discovery of the condition. The vacuum breakers will fail open on the loss of electrical control power. Operator actions could also address this condition in an applicable design-basis scenario.
This event is considered a safety system functional failure per NEI 99-02.
E. CORRECTIVE ACTIONS
Immediate:
- 1. Valve 1-1601-84B was returned to the open position.
Follow-up:
- 1. New default position for the valve will be 'Locked Open.'
- 2. Startup procedures will be revised to verify the position of the valve.
- 3. Training will be provided for the Operations Department related to this event.
F. PREVIOUS OCCURENCES
The station events database, LERs and IRIS were reviewed for similar events at Quad Cities Nuclear Power Station. Two station LERs in the last three years listed below include events where written instructions were not properly recognized or followed by Operations, resulting in TS violations.
LER (254/2024-01-00) Technical Specification 3.5.2 Action Not Performed Due to Inadequate Procedure Adherence, 1/21/25. Procedure adherence related issue resulted in a Reactor Pressure Vessel Water Inventory Control (RPV WIC) drainage event. Associated with that event was a failure to recognize the need to enter RPV WIC related TS Actions.
LER (254/2025-001-00) Technical Specification 3.6.4.2 Not Performed Due to Tagout Boundary Placement Error, 3/7/25. Failure to implement the administrative controls in a tagout resulted in a secondary containment isolation valve being left in an open position.
G. COMPONENT FAILURE DATA
There were no equipment failures associated with this event.
This event has been reported to IRIS. Page _4_ of _4_