ML25111A208
| ML25111A208 | |
| Person / Time | |
|---|---|
| Site: | Cooper  |
| Issue date: | 04/24/2025 |
| From: | Douglas Dodson NRC/RGN-IV/DORS/PBC |
| To: | John Monninger NRC Region 4 |
| Dodson D | |
| References | |
| MD 8.3 | |
| Download: ML25111A208 (1) | |
Text
April 24, 2025 MEMORANDUM TO:
John D. Monninger, Regional Administrator THRU:
Geoffrey B. Miller, Director Division of Operating Reactor Safety FROM:
Douglas E. Dodson II, Chief Reactor Projects Branch C Division of Operating Reactor Safety
SUBJECT:
MANAGEMENT DIRECTIVE 8.3 EVALUATION FOR COOPER NUCLEAR STATION DIESEL GENERATOR 1 JACKET WATER PUMP FAILURE ON APRIL 8, 2025, AND DIESEL GENERATOR 2 JACKET WATER AND NON-EMERGENCY TRIP BYPASS VALVE ISSUES Pursuant to Regional Office Policy Guide 0801.6, Management Directive 8.3 and Inspection Manual Chapter 0309 Reactive Team Inspection Decisions, Implementation, and Documentation for Power Reactors, the enclosed table provides the Management Directive 8.3 evaluation associated with the inoperability of Cooper Nuclear Stations division I emergency diesel generator during a monthly surveillance on April 8, 2025. During a planned surveillance of the division I emergency diesel generator, jacket cooling water pressure was found out of specification low after 15 minutes of operation; operators secured the diesel and declared it inoperable. The impeller of the jacket water pump was found loose, and maintenance had been performed on the pump in February. In January 2025 and March 2025, the division II emergency diesel generator also experienced unplanned inoperability associated with jacket water leakage and a failure to start during testing due to a failed non-emergency trip bypass valve, respectively.
Staff performed this evaluation to determine the risk significance of the event to determine the appropriate level of the U.S. Nuclear Regulatory Commission response. Based on this evaluation, the staff recommends that no additional reactive inspection be performed for follow-up of this event at the Cooper Nuclear Station.
Concur with Recommendation:
Regional Administrator Date
Enclosures:
MD 8.3 Decision Documentation Form (Deterministic and Risk Criteria Analyzed)
CONTACT: Douglas E. Dodson II, DORS/PBC 817-200-1148 Signed by Miller, Geoffrey on 04/23/25 Signed by Dodson, Douglas on 04/22/25 Signed by Monninger, John on 04/24/25
ML25111A208 SUNSI Review ADAMS:
Non-Publicly Available Non-Sensitive Keyword:
By: DXO Yes No Publicly Available Sensitive MD 8.3 OFFICE PE:DORS/PBC SRI:DORS/PBC SRA:DORS BC:DORS/PBC D:DORS RA NAME DOuk GKolcum RDeese DDodson GMiller JMonninger SIGNATURE
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DATE 04/22/25 04/22/25 04/22/25 04/22/25 04/23/25 04/25/25
Enclosure MANAGEMENT DIRECTIVE 8.3 DECISION DOCUMENTATION FORM (Deterministic and Risk Criteria Analyzed)
PLANT:
Cooper Nuclear Station EVENT DATE:
April 8, 2025 RESPONSIBLE BRANCH CHIEF:
Douglas Dodson EVALUATION DATE:
April 11, 2025 BRIEF DESCRIPTION OF THE SIGNIFICANT OPERATIONAL EVENT OR DEGRADED CONDITION:
On April 8, 2025, Cooper Nuclear Station operators secured the division I emergency diesel generator and declared it inoperable approximately 15 minutes after reaching full load and approximately 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> into the 3.5-hour monthly surveillance run.
During the surveillance, operators noticed that jacket water pressure measured only 5 pounds per square inch (psi) as opposed to normal jacket water cooling pressures of approximately 20 psi. Upon further investigation, the station determined that the jacket water pump was inoperable due to the pump impeller not being secure on the pump shaft.
Two months prior to the event, on February 5, 2025, the station replaced the pump seals on the division I emergency diesel generator jacket water pump. During this maintenance, the pump impellor was removed and then reinstalled. On March 3, 2025, the division I emergency diesel generator passed its monthly surveillance and operated for approximately 3.5-hours.
The station also experienced two other recent diesel generator issues associated with the division II emergency diesel generator. Specifically, on January 22, 2025, a jacket water leak on the 1R cylinder was quantified above allowable technical specification limits, and the division II diesel generator was declared inoperable. Jacket water inventory is impacted when leakage exceeds 239 drops per minute (dpm), and the diesel generator jacket water leakage was approximately 360 dpm. The division II diesel generator was repaired and declared operable on January 25, 2025.
Additionally, on March 17, 2025, the division II diesel generator failed to start during its monthly surveillance run that incorporated an annual test of the non-emergency trip bypass solenoid valve, which was last tested satisfactorily on March 11, 2024. The licensee determined the solenoid valve failed in the intermediate position, which resulted in the fuel control cylinder blocking fuel supply. On March 19, 2024, the station returned the division II diesel generator to service and operable after replacing the solenoid valve.
2 Y/N DETERMINISTIC CRITERIA Involved operations that exceeded, or were not included in, the design bases of the facility N
Remarks: Based on available information at the time of this evaluation, it appears the division I diesel generator was inoperable after maintenance of the jacket water pump in February 2025, resulting in the division I and division II diesel generator both being rendered inoperable at the same time in March 2025.
However, the event under evaluation was within the design bases of the facility as offsite power was still available for emergency loads.
Involved a major deficiency in design, construction, or operation having potential generic safety implications N
Remarks: Based on available information at the time of this evaluation, the inoperability of the division I and II diesels were not associated with major deficiencies in design, construction, or operation of the facility and do not have generic safety implications.
Led to a significant loss of integrity of the fuel, primary coolant pressure boundary, or primary containment boundary of a nuclear reactor N
Remarks: While inoperability of both divisions of diesel generators could result in the loss of major safety systems, none of the issues under evaluation resulted in a loss of integrity of the fuel, primary coolant pressure boundary, or the primary containment boundary.
Led to the loss of a safety function or multiple failures in systems used to mitigate an actual event Y
Remarks: Simultaneous inoperability of the division I and II diesel generators represents the loss of the emergency power sources for the 4 kV 1F and 1G emergency buses, respectively, which could lead to multiple failures in systems used to mitigate an actual event, including, but not limited to, safety related service water, service water booster pumps, residual heat removal pumps, and core spray pumps. Based on available information at the time of this evaluation, it appears that the safety related diesel generators would have been simultaneously inoperable at various points from the time the jacket water pump was removed from service on February 5, 2025, until it failed on April 8, 2025.
Involved possible adverse generic implications N
Remarks: Based on available information at the time of this evaluation, inoperability of the division I and II diesel generators does not represent adverse generic safety implications.
Involved significant unexpected system interactions N
Remarks: Based on available information at the time of this evaluation, although inoperability of two trains of emergency power is unexpected, inoperability of the division I and II diesel generators neither represents nor involved significant unexpected system interactions.
3 Y/N DETERMINISTIC CRITERIA Involved repetitive failures or events involving safety-related equipment or deficiencies in operations Y
Remarks: The inoperability of the division I diesel generator occurred from loss of jacket cooling water pressure. Best available information at the time of this evaluation suggests maintenance practices contributed to the division I diesel generator jacket water pump failure. Additionally, the division II diesel generator experienced two noteworthy issues in the first quarter of 2025 related to excessive leaking of jacket water and improper valve positioning of the non-emergency trip bypass solenoid valve. These issues resulted in the division II diesel generator being declared inoperable twice in this period, and best available information suggests maintenance practices may have also contributed to one or both of these adverse impacts to safety-related equipment. Hence, the staff determined that these issues involved repetitive failures or events involving safety-related equipment, the safety-related diesel generators.
Involved questions or concerns pertaining to licensee operational performance N
Remarks: Based on available information at the time of this evaluation, the staff did not identify any concerns pertaining to licensee operational performance.
4 CONDITIONAL RISK ASSESSMENT IF IT IS DETERMINED THAT A RISK ANALYSIS IS NOT REQUIRED - ENTER NA BELOW AND CONTINUE TO THE DECISION BASIS BLOCK RISK ANALYSIS BY:
Rick Deese DATE: April 17, 2025 Brief description for the basis of the assessment (may include assumptions, calculations, references, peer review, or comparison with licensees results):
The analyst assumed the following:
1.
The jacket water leaks on both diesel generators did not threaten the probabilistic risk assessment mission time for either diesel generator, therefore the only risk accrued for jacket water leakage was when the diesels were taken out of service to repair the leakage.
2.
The degradation of the diesel generator 2 emergency trip solenoid represented an increased trip probability since the diesel would additionally trip on non-essential trip signals and conditions. The basic event EPS-DGN-FR-DG1B, Diesel Generator 1B Fails to Run, was increased to 4.44E-3 to model the increased trip probability.
3.
The low jacket water pressure condition on diesel generator 1 represented a failure to run event which was present from restoration from maintenance on February 5, 2025, until its surveillance run on April 8, 2025. Since the maintenance, which was believed to induce the failure was unique to diesel generator 1, common cause failure of diesel generator 2 was not adjusted (basic event EPS-DGN-FR-DG1A, Diesel Generator 1A Fails to Run, was set to 1.0).
4.
Because the jacket water pump worked on the diesel generators February post-maintenance test, February and March surveillance tests, and for a short time during the April surveillance test before its failure, credit was deemed applicable for the time the diesel could have successfully mitigated an event. Due to the complexity of the evaluation needed to calculate the credit, an adjustment factor was estimated at 0.70 based on previous similar evaluations and applied to each unique risk-significant operational window of the exposure time.
5.
The licensees FLEX strategies and equipment were available for implementation for the exposure period and therefore credit was given for station mitigation capabilities.
6.
For the various risk-significant equipment outages (e.g., supplemental diesel generator, station startup transformer, high pressure coolant injection, reactor core isolation cooling, etc.) between February 5, 2025, and April 8, 2025, the increase in conditional core damage probability (CCDP) was assessed by comparing the CCDP of just taking the equipment out of service and taking that equipment out of service with basic event EPS-DGN-FR-DG1A, Diesel Generator 1A Fails to Run, set to 1.0.
The Cooper SPAR model, version 8.22, ran on SAPHIRE, version 8.2.11, was used in this evaluation to estimate the risk impact for internal events and all external events except for fire events. For fire events, the analyst used the licensees NFPA 805 approved fire model results. The assumptions applied to the probabilistic risk assessment tools mentioned above yielded an estimate of the increase in conditional core damage probability of 4.7E-6.
The analyst spoke with the licensees probabilistic risk assessment staff on April 16, 2025.
The licensee provided their estimate of change in core damage probability of 4.47E-7.
5 CONDITIONAL RISK ASSESSMENT The licensee told the analyst that their estimate of conditional core damage probability was based on internal events risk only and did not include fire risk. The analyst noted that application of fire risk using the licensees probabilistic risk assessment performance measures would add approximately 4E-6 to their estimate of conditional core damage probability.
THE ESTIMATED INCREMENTAL CONDITIONAL CORE DAMAGE PROBABILITY (CCDP) IS:
4.7E-6 WHICH PLACES THE RISK IN THE RANGE OF:
No Additional Inspection/Special Inspection Overlap
6 RESPONSE DECISION USING THE ABOVE INFORMATION AND OTHER KEY ELEMENTS OF CONSIDERATION AS APPROPRIATE, DOCUMENT THE RESPONSE DECISION TO THE EVENT OR CONDITION, AND THE BASIS FOR THAT DECISION DECISION AND DETAILS OF THE BASIS FOR THE DECISION: The recommendation is not to perform a reactive inspection at this time. The inoperability of the division I diesel generator occurred from loss of jacket cooling water pressure, and best available information at the time of this evaluation suggests maintenance practices in February 2025 contributed to the division I diesel generator jacket water pump failure in April 2025. Additionally, the division II diesel generator experienced two noteworthy issues in the first quarter of 2025, which included excessive leaking of jacket water and improper valve positioning of the non-emergency trip bypass solenoid valve. These noteworthy issues resulted in the division II diesel generator being declared inoperable twice in this period, and best available information suggests maintenance practices may have also contributed to one or both of these adverse impacts to safety-related equipment.
While these facts and best available information at the time of the evaluation led the staff to note two deterministic criteria were meta loss of safety function and repetitive failures or events involving the safety-related diesel generatorsand the risk assessment determined that risk was in the upper portion of the no additional reactive inspection and lower portion of the special inspection range, the staff has already gathered sufficient facts to expeditiously evaluate these issues, commensurate with their safety significance, using the normal baseline inspection program.
Hence, the recommendation is to follow-up on these issues using the normal baseline inspection program to better understand the failures and licensee maintenance practices.
BRANCH CHIEF REVIEW:
Douglas Dodson DATE:
April 22, 2025 DIVISION DIRECTOR REVIEW:
Geoffrey Miller DATE:
April 23, 2025 ADAMS ACCESSION NUMBER: ML25111A208 EVENT NOTIFICATION REPORT NUMBER (as applicable):
E-mail to NRR_Reactive_Inspection@nrc.gov
REACTOR SAFETY Y/N IIT Deterministic Criteria Led to a Site Area Emergency N
Remarks: The event did not lead to a Site Area Emergency declaration.
Exceeded a safety limit of the licensee's technical specifications N
Remarks: The event did not result in exceeding any safety limits as defined in chapter 2.0, Safety Limits (SLs), of the licensees technical specifications.
Involved circumstances sufficiently complex, unique, or not well enough understood, or involved safeguards concerns, or involved characteristics the investigation of which would best serve the needs and interests of the Commission N
Remarks: The staff assessed the event was sufficiently similar to other failures such that the event could be evaluated using available risk assessment methods; therefore, the staff determined that the event did not involve circumstances sufficiently complex, unique, or not well enough understood such that an incident investigation team was necessary to best serve the needs and interests of the Commission. Additionally, the event circumstances did not involve safeguard concerns.
Y/N SI Deterministic Criteria Significant failure to implement the emergency preparedness program during an actual event, including the failure to classify, notify, or augment onsite personnel N
Remarks: The event did not involve a failure to implement the emergency preparedness program; there were no known failures to classify, notify, or augment onsite personnel.
Involved significant deficiencies in operational performance which resulted in degrading, challenging, or disabling a safety system function or resulted in placing the plant in an unanalyzed condition for which available risk assessment methods do not provide an adequate or reasonable estimate of risk N
Remarks: The event did not involve significant deficiencies in operational performance.
7
RADIATION SAFETY Y/N IIT Deterministic Criteria Led to a significant radiological release (levels of radiation or concentrations of radioactive material in excess of 10 times any applicable limit in the license or 10 times the concentrations specified in 10 CFR Part 20, Appendix B, Table 2, when averaged over a year) of byproduct, source, or special nuclear material to unrestricted areas N
Remarks: The event did not lead to a radiological release.
Led to a significant occupational exposure or significant exposure to a member of the public. In both cases, significant is defined as five times the applicable regulatory limit (except for shallow-dose equivalent to the skin or extremities from discrete radioactive particles)
N Remarks: The event did not lead to occupational exposure.
Involved the deliberate misuse of byproduct, source, or special nuclear material from its intended or authorized use, which resulted in the exposure of a significant number of individuals N
Remarks: The event did not involve the deliberate misuse of byproduct, source, or special nuclear material from its intended or authorized use.
Involved byproduct, source, or special nuclear material, which may have resulted in a fatality N
Remarks: The event did not involve byproduct, source, or special nuclear material or result in any fatalities.
Involved circumstances sufficiently complex, unique, or not well enough understood, or involved safeguards concerns, or involved characteristics the investigation of which would best serve the needs and interests of the Commission N
Remarks: The staff assessed the event was sufficiently similar to other failures such that the event could be evaluated using available risk assessment methods; therefore, the staff determined that the event did not involve circumstances sufficiently complex, unique, or not well enough understood such that an incident investigation team was necessary to best serve the needs and interests of the Commission. Additionally, the event circumstances did not involve safeguard concerns.
8
RADIATION SAFETY Y/N AIT Deterministic Criteria Led to a radiological release of byproduct, source, or special nuclear material to unrestricted areas that resulted in occupational exposure or exposure to a member of the public in excess of the applicable regulatory limit (except for shallow-dose equivalent to the skin or extremities from discrete radioactive particles)
N Remarks: The event did not involve the radiological release of byproduct, source, or special nuclear material to unrestricted areas that resulted in occupational exposure or exposure to a member of the public.
Involved the deliberate misuse of byproduct, source, or special nuclear material from its intended or authorized use and had the potential to cause an exposure of greater than 5 rem to an individual or 500 mrem to an embryo or fetus N
Remarks: The event did not involve the deliberate misuse of byproduct, source, or special nuclear material from its intended or authorized use.
Involved the failure of radioactive material packaging that resulted in external radiation levels exceeding 10 rads/hour or contamination of the packaging exceeding 1,000 times the applicable limits specified in 10 CFR 71.87 N
Remarks: The event did not involve the failure of radioactive material packaging.
Involved the failure of the dam for mill tailings with substantial release of tailings material and solution off site N
Remarks: The event did not involve the failure of a dam for mill tailings that resulted in the release of tailings material.
9
Y/N SI Deterministic Criteria May have led to an exposure in excess of the applicable regulatory limits, other than via the radiological release of byproduct, source, or special nuclear material to the unrestricted area; specifically occupational exposure in excess of the regulatory limits in 10 CFR 20.1201 exposure to an embryo/fetus in excess of the regulatory limits in 10 CFR 20.1208 exposure to a member of the public in excess of the regulatory limits in 10 CFR 20.1301 N
Remarks: The event did not lead to an exposure in excess of the applicable regulatory limits.
May have led to an unplanned occupational exposure in excess of 40 percent of the applicable regulatory limit (excluding shallow-dose equivalent to the skin or extremities from discrete radioactive particles)
N Remarks: The event did not lead to an unplanned occupational exposure in excess of 40 percent of the applicable regulatory limit.
Led to unplanned changes in restricted area dose rates in excess of 20 rem per hour in an area where personnel were present or which is accessible to personnel N
Remarks: The event did not lead to unplanned changes in restricted area dose rates in excess of 20 rem per hour.
Led to unplanned changes in restricted area airborne radioactivity levels in excess of 500 DAC in an area where personnel were present or which is accessible to personnel and where the airborne radioactivity level was not promptly recognized and/or appropriate actions were not taken in a timely manner N
Remarks: The event did not lead to unplanned changes in restricted area airborne radioactivity levels.
Led to an uncontrolled, unplanned, or abnormal release of radioactive material to the unrestricted area for which the extent of the offsite contamination is unknown; or that may have resulted in a dose to a member of the public from loss of radioactive material control in excess of 25 mrem (10 CFR 20.1301(e)); or that may have resulted in an exposure to a member of the public from effluents in excess of the ALARA guidelines contained in Appendix I to 10 CFR Part 50 N
Remarks: The event did not lead to an uncontrolled, unplanned, or abnormal release of radioactive material.
Led to a large (typically greater than 100,000 gallons), unplanned release of radioactive liquid inside the restricted area that has the potential for ground-water or offsite contamination N
Remarks: The event did not lead to a large, unplanned release of radioactive liquid inside the restricted area.
10
Y/N SI Deterministic Criteria Involved the failure of radioactive material packaging that resulted in external radiation levels exceeding 5 times the accessible area dose rate limits specified in 10 CFR Part 71, or 50 times the contamination limits specified in 49 CFR Part 173 N
Remarks: The event did not involve the failure of radioactive material packaging.
Involved an emergency or non-emergency event or situation, related to the health and safety of the public or on-site personnel or protection of the environment, for which a 10 CFR 50.72 report has been submitted that is expected to cause significant, heightened public or government concern N
Remarks: The event is not expected to cause significant heightened public or government concern.
SAFEGUARDS/SECURITY Y/N IIT Deterministic Criteria Involved circumstances sufficiently complex, unique, or not well enough understood, or involved safeguards concerns, or involved characteristics the investigation of which would best serve the needs and interests of the Commission N
Remarks: The staff assessed the event was sufficiently similar to other issues/events such that the event could be evaluated using available risk assessment methods; therefore, the staff determined that the event did not involve circumstances sufficiently complex, unique, or not well enough understood such that an incident investigation team was necessary to best serve the needs and interests of the Commission.
Additionally, the event circumstances did not involve safeguard concerns.
Failure of licensee significant safety equipment or adverse impact on licensee operations as a result of a safeguards-initiated event (e.g., tampering)
N Remarks: The event did not involve an adverse impact on safety equipment or licensee operations as a result of a safeguards-initiated event.
Actual intrusion into the protected area N
Remarks: The event did not involve an actual intrusion into the protected area.
Y/N AIT Deterministic Criteria Involved a significant infraction or repeated instances of safeguards infractions that demonstrate the ineffectiveness of facility security provisions N
Remarks: The event did not involve a significant infraction or repeated instances of safeguards infractions.
11
Y/N AIT Deterministic Criteria Involved repeated instances of inadequate nuclear material control and accounting provisions to protect against theft or diversions of nuclear material N
Remarks: The event did not involve repeated instances of inadequate nuclear material control and accounting provisions.
Confirmed tampering event involving significant safety or security equipment N
Remarks: The event did not involve tampering of safety or security equipment.
Substantial failure in the licensees intrusion detection or package/personnel search procedures which results in a significant vulnerability or compromise of plant safety or security N
Remarks: The event did not involve a substantial failure in the licensees intrusion detection or package/personnel search procedures.
Y/N SI Deterministic Criteria Involved inadequate nuclear material control and accounting provisions to protect against theft or diversion, as evidenced by inability to locate an item containing special nuclear material (such as an irradiated rod, rod piece, pellet, or instrument)
N Remarks: The event did not involve inadequate nuclear material control and accounting provisions.
Involved a significant safeguards infraction that demonstrates the ineffectiveness of facility security provisions N
Remarks: The event did not involve a significant safeguards infraction.
Confirmation of lost or stolen weapon N
Remarks: The event did not involve a lost or stolen weapon.
Unauthorized, actual non-accidental discharge of a weapon within the protected area N
Remarks: The event did not involve the unauthorized, actual non-accidental discharge of a weapon.
Substantial failure of the intrusion detection system (not weather-related)
N Remarks: The event did not involve the substantial failure of the intrusion detection system.
Failure to the licensees package/personnel search procedures which results in contraband or an unauthorized individual being introduced into the protected area N
Remarks: The event did not involve a failure in the licensees package/personnel search procedures.
12
N Potential tampering or vandalism event involving significant safety or security equipment where questions remain regarding licensee performance/response or a need exists to independently assess the licensees conclusion that tampering or vandalism was not a factor in the condition(s) identified 13