05000237/LER-2024-001, Containment Cooling Service Water Valve Failure Resulted in a Condition Prohibited by Technical Specifications and Loss of Safety Function
| ML25027A435 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 01/27/2025 |
| From: | Joseph C Constellation Energy Generation |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| SVPLTR 25-0005 LER 2024-001-00 | |
| Download: ML25027A435 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat |
| 2372024001R00 - NRC Website | |
text
Constellation,
January 27, 2025 SVPL TR: #25-0005 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Dresden Nuclear Power Station, Unit 2 Renewed Facility Operating License No. DPR-19 NRC Docket No. 50-237 Dresden Nuclear Power Station 6500 North Dresden Road Morris, IL 60450 10 CFR 50.73
Subject:
Licensee Event Report 237/2024-001-00, Containment Cooling Service Water Valve Failure Resulted in a Condition Prohibited by Technical Specifications and Loss of Safety Function Enclosed is Licensee Event Report 237/2024-001-00, Containment Cooling Service Water Valve Failure Resulted in a Condition Prohibited by Technical Specifications and Loss of Safety Function. This report describes an event being reported in accordance with 10 CFR
- 50. 73(a)(2)(i)(B), 10 CFR 50. 73(a)(2)(v)(B), and 10 CFR 50. 73(a)(2)(v)(D) for an Operation or Condition Prohibited by Technical Specifications and an Event or Condition that Could Have Prevented Fulfillment of a Safety Function.
There are no regulatory commitments contained in this submittal.
Should you have any questions concerning this letter, please contact Mr. Daniel J. Murphy, Regulatory Assurance Manager, at (779) 231-7443.
Respectfully,
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Carolyne Josepti Site Vice President Dresden Nuclear Power Station
Enclosure:
Licensee Event Report 237/2024-001-00 CC:
Regional Administrator - NRC Region Ill NRC Senior Resident Inspector - Dresden Nuclear Power Station
Abstract
On 4/30/2024 at 10:07 CST when starting a Containment Cooling Service Water (CCSW) Pump, the Dresden Unit 2 Containment Cooling Heat Exchanger Division I Tube Side Discharge Valve failed to open. The safety related function of the valve is to control cooling water flow through the heat exchanger tubes to remove heat from containment. The condition was corrected at 03:10 on 5/1/2024. The station determined the Division I CCSW system was inoperable for 28.5 days, therefore, an Operation or Condition Prohibited by Technical Specifications existed for greater than the Limiting Condition of Operation (LCO) time of 7 days. During this period, surveillance testing performed on 4/3/2024 resulted in the Division II subsystem being inoperable for 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> and 39 minutes resulting in an Event or Condition that Could Have Prevented Fulfillment of a Safety Function. The cause of the event was due to overtravel of the valve position potentiometer during valve closure, resulting in removal of an open permissive in the valve's control logic which was corrected by potentiometer and valve stroke length adjustments.
This report is being submitted under 10 CFR 50.73(a)(2)(i)(B), 10 CFR 50.73(a)(2)(v)(B) and 10 CFR
- 50. 73(a)(2)(v)(D).
PLANT AND SYSTEM IDENTIFICATION
- 2. DOCKET NUMBER YEAR 00237 2024 -
- 3. LER NUMBER SEQUENTIAL NUMBER 001 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].
CONDITIONS PRIOR TO EVENT
Unit: 2 Reactor Mode: 1 Event Date: April 30, 2024 Mode Name: Power Operation Event Time: 10:07 CST Power Level: 100 percent No structures, systems, or components were inoperable at the time of the event that contributed to the event.
A. DESCRIPTION OF EVENT
On 4/30/2024 at 10:07 CST, with Dresden Unit 2 at 100 percent power, while performing operations to support Suppression Pool [BO] level control, no CCSW [Bl] flow was observed on the instrumentation in the Main Control Room (MCR) following system start. When 2A CCSW [Bl] Pump was started per Dresden Operating Procedures, the Heat Exchanger [HX] 'A' Tube Side Discharge Valve [PDCV] did not automatically open (dual indication) as expected. The system is designed to remove energy from the suppression pool [NH] by rejecting heat to the CCSW [Bl] system. Suppression pool cooling [BO] or containment [NH] sprays may be initiated following a Loss of Coolant Accident (LOCA) using a portion of the non-selected Low Pressure Coolant Injection (LPCI) [BO] loop, which is not required to perform a LPCI [BO] function. When CCSW [Bl] is initiated, the Heat Exchanger [HX] 'A' Tube Side Discharge Valve [PDCV] is designed to open based on demand from a Differential Pressure (DP) Controller [PDC].
A past operability review was completed on 6/20/2024 and determined that the Heat Exchanger [HX] 'A' Tube Side Discharge Valve [PDCV] was incapable of performing its function after the valve [PDCV] was opened and closed for Post Maintenance Testing (PMT) at 14:24 CST on 4/2/2024. This was not discovered until the past operability was reviewed for reporting criteria on 11/27/2024 and determined to be reportable under 10 CFR 50.73.
When the Heat Exchanger [HX] 'A' Tube Side Discharge Valve [PDCV] failed to open, Technical Specification (TS) 3.7.1 Conditions A and C were entered for Division 1 CCSW [Bl] being declared inoperable. Division 1 Suppression Pool Cooling [BO], Suppression Pool [NH] Spray and Drywell [NH] Spray were also INOPERABLE (TS 3.6.2.3, 3.6.2.4 and 3.6.2.6 respectively). The Limiting Condition of Operation (LCO) time for one subsystem inoperable is 7 days, therefore an Operation or Condition Prohibited by TS existed from 4/9/2024 14:24 CST to 5/1/2024 03:10 CST. This is being reported under 10 CFR 50.73(a)(2)(i)(B).
Additionally, from 00:42 to 04:21 CST on 4/3/2024, the opposite Division II CCSW [Bl], Suppression Pool Cooling [BO], Suppression Pool [NH] Spray and Drywell [NH] Spray were inoperable due to surveillance testing on Unit 2 LPCI [BO] Initiation circuitry. This also resulted in an Event or Condition that Could Have
- 2. DOCKET NUMBER
- 3. LER NUMBER YEAR SEQUENTIAL REV NUMBER NO.
00237 2024 -
001 00 Prevented Fulfillment of a Safety Function and is being reported under 10 CFR 50. 73(a)(2)(v)(B) and 10 CFR
- 50. 73(a)(2)(v)(D).
8. CAUSE OF EVENT
The Heat Exchanger [HX] 'A' Tube Side Discharge Valve [PDCV] failed to open from the MCR due to potentiometer [FD] over-range feedback causing the downstream relay [RL Y] to remain open. Without this open permissive being made up, the valve [PDCV] was unable to be operated from the MCR. Evaluation concluded the failure mechanism to be due to low margin on the valve [PDCV] potentiometer [FD] position during valve [PDCV] stoke. The valve [PDCV] stroke length was found to be using nearly the full band of the potentiometer [FD] and created opportunity for overtravel into the dead-band region when the valve [PDCV] is taken to either the full open or full closed positions.
The valve [PDCV] had previously been cycled open and closed at 14:24 on 4/2/24 as part of PMT. The valve [PDCV] was not operated again until the failure identified at 10:07 on 4/30/24. On 4/2/24 the potentiometer [FD] would have over-traveled and caused a failure to open at the next open demand from the Differential Pressure (DP) Controller [PDC] within the MCR. This condition would not have been apparent until the next attempt to operate the valve [PDCV] via the MCR. With the failure mechanism being associated with the potentiometer [FD] over-travelling when the valve [PDCV] is taken to full close, there is reasonable assurance the valve [PDCV] would have performed its function prior to 4/2/24.
C. SAFETY ANALYSIS
The Dresden Updated Final Safety Analysis Report (UFSAR) long-term Design Basis Accident-LOCA (DBA-LOCA) analysis assumes one Containment Cooling loop [BO] with one heat exchanger [HX] is available for containment [NH] cooling, being manually initiated at 10 minutes. Assuming the suppression pool [NH] and CCSW [Bl] initial temperature is at TS limits of 95 degrees Fahrenheit, the peak suppression pool [NH]
temperature is 196 degrees Fahrenheit. The heat removal capability of one subsystem is sufficient to meet the overall OBA cooling requirement for LOCAs and transient events. Additional margin to containment limits is provided by nominal plant parameters.
For 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> and 39 minutes, while in Modes 1, 2 and 3, both divisions of Suppression Pool Cooling [BO],
Suppression Pool [NH] Spray and Drywell [NH] Spray were inoperable. Division I was inoperable due to the U2 Heat Exchanger [HX] 'A' Tube Side Discharge Valve [PDCV], preventing CCSW [Bl] flow. Division II was inoperable due to LPCI [BO] pump breakers [BKR] being racked to test. In this condition, LPCI [BO] flow from Division I was capable of providing flow to containment [NH] sprays. Without cooling from CCSW [Bl], this spray flow would cool noncondensible gases, condense steam, and assist the natural convection and diffusion mixing of hydrogen and oxygen in the containment following a postulated LOCA. The flow would also continue to provide scrubbing by the containment [NH] sprays to reduce the activity of elemental iodine and aerosols released from the core.
With two subsystems inoperable, an 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> Completion Time to restore one is based on the loss of function, and is considered acceptable due to the low probability of a OBA and the potential avoidance of a plant shutdown transient that could result in the need for the subsystems to operate. Operators were able to cycle
- 2. DOCKET NUMBER
- 3. LER NUMBER YEAR SEQUENTIAL REV NUMBER NO.
00237 2024 -
001 00 the U2 Heat Exchanger [HX] 'A' Tube Side Discharge Valve [PDCV] locally using operating procedures.
Additionally, operators had been briefed, were standing by, and at least one LPCI [BO] pump on Division II would have been able to be restored in approximately 10 minutes, with the second LPCI [BO] pump being restored two to three minutes later. During a LOCA (assuming conservative 10 CFR 50 Appendix K model numbers), peak cladding temperature reaches 2136 degrees Fahrenheit, which will result in some fuel failure and an increase in radiation in the areas required to restore at least one division. During nominal plant operational parameters, fuel cladding remains below 1500 degrees Fahrenheit following a DBA-LOCA, and therefore, based on Engineering Judgement, the radiation and temperatures in these areas is expected at levels commensurate with normal operating conditions. During the 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> and 39 minutes, suppression pool [NH] temperature was a nominal 79 degrees Fahrenheit, CCSW [Bl] was a nominal 77 degrees Fahrenheit, providing additional margin to limits.
A. CORRECTIVE ACTIONS
Corrective actions adjusted the potentiometer [FD] and the stroke length for the Heat Exchanger [HX] 'A' Tube Side Discharge Valve [PDCV].
Long-term corrective actions are to perform:
Contingency extent of condition adjustments of the other division and Dresden Unit 3 Heat Exchanger [HX]
Tube Side Discharge Valves [PDCV] are planned. However, these three have been verified to have margin on the potentiometers [FD] during valve [PDCV] cycling.
8. PREVIOUS OCCURRENCES
A review of the internal Corrective Action Program (CAP) was performed.
The Heat Exchanger [HX] 'A' Tube Side Discharge Valve [PDCV] failed in a similar manner on 11/14/2023.
While returning the system to service, the U2 Containment Cooling Heat Exchanger [HX] 'A' Tube Side Discharge Valve [PDCV] failed to open after start of 2A or 28 CCSW [Bl] pumps. This issue is being investigated separately.
C. COMPONENT FAILURE DATA
System: Bl Component: FD Manufacturer: 8135 Nomenclature: Single Turn Potentiometer Model Number: 5611 R 1 KL.5 Page _4_ of _ 4 _