ML25258A143
| ML25258A143 | |
| Person / Time | |
|---|---|
| Site: | Oconee  (DPR-038) |
| Issue date: | 09/17/2025 |
| From: | Robert Williams NRC/RGN-II/DORS/PB1 |
| To: | |
| References | |
| MD 8.3 | |
| Download: ML25258A143 (11) | |
Text
1 : Decision Documentation for Reactive Inspection (Deterministic and Risk Criteria Analyzed)
Decision Documentation for Reactive Inspection (Deterministic and Risk Criteria Analyzed)
Note: The results of this assessment are based on an initial or preliminary set of information and do not prejudge or imply deficient performance on the part of the licensee or the lack thereof. The purpose of this assessment is to determine whether to conduct a reactive inspection; it is independent of determining the significance of any inspection findings that may be associated with these circumstances.
PLANT: Oconee Unit 1 EVENT DATE: 9/10/2025 EVALUATION DATE: 9/10-11/2025 Brief Description of the Significant Event or Degraded Condition:
On September 10, 2025, at 1138 eastern daylight time (EDT), Oconee Unit 1 control room operators were notified of leakage coming from the 1A letdown filter housing. At 1152 EDT, operators noted reactor coolant system (RCS) leakage of ~26 gallons per minute (gpm) into the auxiliary building. The leakage persisted for greater than 15 minutes. The licensee declared a Notice of Unusual Event (NOUE) at 1207 EDT for identified RCS leakage greater than 25 gpm for greater than 15 minutes (SU5.1). The 1B letdown filter was out of service due to planned maintenance. The licensee immediately initiated actions to isolate the 1A letdown filter, and declared the leak isolated at 1234 EDT. The 1B letdown filter was returned to service, and the licensee exited the NOUE declaration at 1353 EDT.
No other safety-related systems were impacted, and all systems performed as expected.
Unit 1 remained in Mode 1, operating at 100% rated thermal power (RTP). Units 2 and 3 remained unaffected, both in Mode 1 and operating at 100% RTP throughout the event.
The licensee determined the leakage was caused by inadvertent maintenance performed on the in-service 1A letdown filter. This maintenance activity was planned for the isolated 1B letdown filter. The licensee reviewed radiation monitor sample results and determined a small release was detected by radiation monitors 1RIA-43, 1RIA-44, and1RIA-45, but did not exceed the high alarm setpoint for any of the three monitors. Based on preliminary NRC evaluations, the release did not challenge any regulatory limits.
The licensee submitted event notification 57914 and 57917.
Y/N DETERMINISTIC CRITERIA Involved operations that exceeded, or were not included in, the design bases of the facility N
Remarks: This event is bounded by a small break loss of coolant accident event, which is part of the design basis.
Involved a major deficiency in design, construction, or operation having potential generic safety implications N
Remarks: The event did not involve a major deficiency having potential generic safety implications.
2 Led to a significant loss of integrity of the fuel, primary coolant pressure boundary, or primary containment boundary of a nuclear reactor N
Remarks: The RCS leakage did not exceed the normal makeup capacity of the high pressure injection (HPI) system (160 gpm). Therefore, this was not considered a loss of the RCS Fission Product Barrier (i.e., fuel, coolant pressure boundary, or primary containment boundary).
Led to the loss of a safety function or multiple failures in systems used to mitigate an actual event N
Remarks: No safety functions were lost, and there were not multiple system failures. All systems responded as expected. Normal makeup was maintained through one of three available high pressure injection pumps.
Involved possible adverse generic implications N
Remarks: The event did not involve adverse generic implications.
Involved significant unexpected system interactions N
Remarks: All systems performed as expected. Normal makeup was maintained through one of three available high pressure injection pumps.
Involved repetitive failures or events involving safety-related equipment or deficiencies in operations N
Remarks: The event did not involve repetitive failures or events.
Involved questions or concerns pertaining to licensee operational performance N
Remarks: While the event did involve isolated human performance errors, the NRC has no immediate significant concerns regarding the licensees overall operational performance.
CONDITIONAL RISK ASSESSMENT RISK ANALYSIS BY: N/A DATE:
Brief Description of the Basis for the Assessment (may include assumptions, calculations, references, peer review, or comparison with licensees results):
Per IMC 0309, Reactive Inspection Decision Basis for Power Reactors, dated 5/28/25, a risk evaluation for this event is not required because none of the deterministic criteria in Enclosure 1 were answered YES.
In this case, because RCS leakage was well within the capacity of the HPI system (26 gpm observed leak rate vs 160 gpm normal makeup capacity) and level was maintained, no plant trip or safeguards actuation was required. Because there was not a transient from the event, the change in risk would be expected to be minimal.
3 The estimated conditional core damage probability (CCDP) is ___________________ and places the risk in the range of a _______________ and ____________________ inspection.
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:
Significant operational events normally require a follow-up inspection sample, using Inspection Procedure 71153, which will be documented in an inspection report. This IMC 0309 evaluation was used to determine whether a reactive inspection was also warranted. Based on the NRC review of the event and that no deterministic criteria from this enclosure were met, no additional reactive inspection is warranted. NRC inspectors responded to the immediate event.
Routine baseline inspection follow-up is recommended, as needed.
Inspection Follow-up Determination: No Reactive Inspection Recommended BRANCH CHIEF REVIEW:
DIVISION DIRECTOR REVIEW: Gregory F. Suber ADAMS ACCESSION NUMBER:
EVENT NOTIFICATION REPORT NUMBER (as applicable): 57914 and 57917 Profiled using template NRR-123 (ML18233A547 (non-public))
4 : Decision Documentation for Reactive Inspection and Examples (Deterministic-only Criteria Analyzed)
Decision Documentation for Reactive Inspection (Deterministic-only Criteria Analyzed)
Note: The results of this assessment are based on an initial or preliminary set of information and do not prejudge or imply deficient performance on the part of the licensee or the lack thereof. The purpose of this assessment is to determine whether to conduct a reactive inspection; it is independent of determining the significance of any inspection findings that may be associated with these circumstances.
PLANT: Oconee Unit 1 EVENT DATE: 9/10/25 EVALUATION DATE:9/10-11/25 Brief Description of the Significant Event or Degraded Condition:
See above.
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.
Exceeded a safety limit of the licensee's technical specifications N
Remarks: The event did not exceed a safety limit 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: This event is not considered complex, unique or not well enough understood such that an NRC inspection would serve the needs and interest of the Commission.
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: This event did not include a significant failure to implement the emergency preparedness program.
5 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: This event did not involve significant deficiencies in operational performance resulting in the plant being in an unanalyzed condition.
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: There was no significant 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: There was no significant occupational exposure or significant exposure to a member of the public.
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: This event did not involve the deliberate misuse of byproduct, source or special nuclear material.
Involved byproduct, source, or special nuclear material, which may have resulted in a fatality N
Remarks: This event did not involve byproduct, source or special nuclear material, nor did it result in a fatality.
N 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
6 Remarks: This event is not considered complex, unique or not well enough understood such that an NRC inspection would serve the needs and interest of the Commission.
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 lead to a radiological release that resulted in exposure to workers or a member of the public in excess of the applicable regulatory limit.
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: This event did not involve the deliberate misuse of byproduct, source, or special nuclear material.
Involved the failure of radioactive material packaging that resulted in external radiation levels exceeding 10 rads/hr or contamination of the packaging exceeding 1000 times the applicable limits specified in 10 CFR 71.87 N
Remarks: This 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: This event did not involve the failure of the dam for mill tailings.
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 a radiological release that resulted in exposure to workers or a member of the public in excess of the applicable regulatory limit.
7 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: This event did not lead to an unplanned occupational exposure in excess of 40 percent of the applicable regulatory limits.
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: This event did not lead 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.
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: This event did not lead to unplanned changes in restricted area airborne radioactivity levels in excess of 500 DAC.
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: Although radiation monitors detected a small release, initial information indicates there was no offsite contamination. Based on preliminary NRC evaluations, no regulatory limits were challenged.
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: This event did not result in a large unplanned release of radioactive liquid inside the restricted area that has the potential for ground-water, or offsite, contamination.
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: This event did not involve the failure of radioactive material packing.
8 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: While this did involve a NOUE declaration and report, the event had no impact on on-site personnel / public health and safety nor protection of the environment; and 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 event was well understood and did not involve safeguards.
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 was not the result of a safeguards-initiated event.
Actual intrusion into the protected area N
Remarks: This event did not involve an 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: This event did not involve safeguards.
Involved repeated instances of inadequate nuclear material control and accounting provisions to protect against theft or diversions of nuclear material N
Remarks: This event did not involve inadequate nuclear material control and accounting provisions to protect against theft or diversions of nuclear material.
9 Confirmed tampering event involving significant safety or security equipment N
Remarks: This event did not involve tampering.
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: This event was not a failure of the 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: This event did not involve nuclear material control and accounting.
Involved a significant safeguards infraction that demonstrates the ineffectiveness of facility security provisions N
Remarks: This event did not involve safeguards.
Confirmation of lost or stolen weapon N
Remarks: This event did not involve a lost or stolen weapon.
Unauthorized, actual non-accidental discharge of a weapon within the protected area N
Remarks: This event did not involve a weapon.
Substantial failure of the intrusion detection system (not weather related)
N Remarks: This event did not involve 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: This event did not involve the package/personnel search procedures.
10 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 N
Remarks: This event did not involve tampering.
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:
Significant operational events normally require a follow-up inspection sample, using Inspection Procedure 71153, which will be documented in an inspection report. This IMC 0309 evaluation was used to determine whether a reactive inspection was also warranted. Based on the NRC review of the event and that no deterministic criteria from this enclosure were met, no additional reactive inspection is warranted. NRC inspectors responded to the immediate event.
Routine baseline inspection follow-up is recommended, as needed.
Inspection Follow-up Determination: No Reactive Inspection Recommended BRANCH CHIEF REVIEW:
Robert Williams DIVISION DIRECTOR REVIEW: GFSuber for MFranke Mark Franke ADAMS ACCESSION NUMBER: ML25258A143 EVENT NOTIFICATION REPORT NUMBER (as applicable): 57914 and 57917 Profiled using template NRR-123 (ML18233A547 (non-public))
Signed by Williams, Robert on 09/16/25 Suber, Gregory signing on behalf of Franke, Mark on 09/17/25