ML24229A133
| ML24229A133 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 08/19/2024 |
| From: | Alan Blamey Division Reactor Projects II |
| To: | |
| References | |
| MD 8.3 24-006 | |
| Download: ML24229A133 (3) | |
Text
Enclosure Table 1: Decision Documentation for Reactive Inspection (Deterministic and Risk Criteria Analyzed)
MD 8.3 24-006 PLANT: Vogtle Unit 2 EVENT DATE: 08/13/2024 EVALUATION DATE: 08/14/2024 Brief Description of the Significant Operational Event or Degraded Condition:
On August 13, at 11:51 EST, Vogtle unit 2 experienced a fire in a 480 VAC to 120 VAC stepdown transformer in the control building. The 120 VAC control power for the B safety related chiller and B control room emergency air filtration unit was lost. The redundant equipment was not affected. Unit 2 is stable and continues to operate at full power. The other units, Vogtle 1, 3, & 4, were unaffected.
The licensee made an ALERT (SA9) emergency declaration at 12:01 EST, due to the FIRE that caused VISIBLE DAMAGE to a SAFETY SYSTEM component needed for the current operating mode.
EN57270 Y/N DETERMINISTIC CRITERIA
- a. Involved operations that exceeded, or were not included in, the design bases of the facility N
Remarks: Design Basis not exceeded.
- b. Involved a major deficiency in design, construction, or operation having potential generic safety implications N
Remarks: No design, construction, or operation deficiencies were noted.
- c. Led to a significant loss of integrity of the fuel, primary coolant pressure boundary, or primary containment boundary of a nuclear reactor N
Remarks: This did not lead to a loss of any fission product barriers.
- d. Led to the loss of a safety function or multiple failures in systems used to mitigate an actual event N
Remarks: Did not lead to a loss of safety function. The 2A ESF Chiller was functional during the event.
- e. Involved possible adverse generic implications N
Remarks: No adverse or generic implications were identified during this review.
- f. Involved significant unexpected system interactions N
Remarks: Unexpected system interactions did not occur.
Enclosure
- g. Involved repetitive failures or events involving safety-related equipment or deficiencies in operations N
Remarks: This is not a repetitive failure. However, there have been transformer failures in the 2015, 2016 and 2017 timeframes. Based on our reviews, Vogtle took comprehensive actions including performance monitoring and replacement of transformers. In the last 5 years, after the actions have been taken, there has only been 1 additional failure, and this does not constitute repetitive failures.
- h. Involved questions or concerns pertaining to licensee operational performance N
Remarks: Did not involve questions pertaining to licensee operational performance.
2 CONDITIONAL RISK ASSESSMENT RISK ANALYSIS BY: Shane Sandal DATE: 8/15/2024 Brief Description of the Basis for the Assessment (may include assumptions, calculations, references, peer review, or comparison with licensees results):
This risk evaluation was performed for information use only as none of the deterministic criteria were met. A Senior Reactor Analyst performed an event assessment using Vogtle SPAR model Version 8.83. The analyst noted that the SPAR model included FIRE risk but did not include a specific fire sequence for the Unit 2 transformer or the fire area that was associated with the event. The fire modeling background information utilized to develop the SPAR model was reviewed and indicated the overall fire risk of the area was low enough to be excluded from the Vogtle SPAR model and that the licensees fire PRA had considered larger ignition sources that had the potential to generate more significant fires than the transformer fire. Additionally, the analyst noted that the 15 KVA transformer associated with the fire event was below 45 KVA lower limit of consideration in fire PRAs discussed in Supplement 1 of NUREG-6850, Fire Probabilistic Risk Assessment Methods Enhancements. The lower limit was based on a review of the combustible content of smaller transformers and concluded that dry transformers with a rating of 45 kVA or less are expected to have insufficient content of combustible material to produce a challenging fire and it was expected that a significant fire escaping the transformers housing was very unlikely. The analyst also noted that although the Unit 2 A-train chiller was considered TS inoperable due to a maintenance-induced, non-seismically qualified configuration of the 2A NSCW pump, the A-train chiller was generally considered functional for non-seismic (i.e., fire) event sequences. There was one approximate 25-minute period of non-functionality when the licensee elected to restore seismic operability of the 2A NSCW pump and the supported chiller would have been considered non-functional during the maintenance configuration change.
Accordingly, the analyst determined that the estimated risk of the event would not be expected to exceed a CCDP of 1E-06 which was consistent with baseline follow up inspection. This determination assumed that the 15 KVA transformer fire would not have resulted in a credible fire scenario that challenged plant stability.
The estimated conditional core damage probability (CCDP) is <1E-06 and places the risk in the range of N/A* and N/A* inspection.
- Risk evaluation performed for information only
3 Table 2: Decision Documentation for Reactive Inspection (Deterministic-only Criteria Analyzed)
PLANT: Vogtle Unit 2 EVENT DATE: 08/13/2024 EVALUATION DATE: 08/15/2024 Brief Description of the Significant Operational Event or Degraded Condition: See above.
REACTOR SAFETY Y/N IIT Deterministic Criteria Led to a Site Area Emergency N
Remarks: No, an ALERT was declared Exceeded a safety limit of the licensee's technical specifications N
Remarks: No Safety Limit was exceeded.
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: No, based on the initial observations made by the residents, it appears the licensee adequately implemented the emergency plan. The licensee made an appropriate emergency declaration within 10 minutes of the fire in the unit 2 control building.
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: Did not involve significant deficiencies in operational performance.
4 RADIATION SAFETY Y/N IIT Deterministic Criteria N
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 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.
N 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 Remarks: 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: Did not involve byproduct, source or SNM and did not result in a fatality.
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 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: Did not lead to a radiological release that exposed workers or 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: This was not the result of deliberate misuse of byproduct, source, or special nuclear material.
5 N
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 Remarks: Did not result in the failure of radioactive material packaging.
N Involved the failure of the dam for mill tailings with substantial release of tailings material and solution off site.
Remarks: Did not result in the failure of a mill tailing dam.
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: 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: Did not lead to an unplanned occupational exposure in excess of 40 percent of the applicable regulatory limits.
N 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.
Remarks: 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.
N 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.
Remarks: Did not lead to unplanned changes in restricted area airborne radioactivity levels in excess of 500 DAC.
6 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: There was no 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 groundwater, or offsite, contamination.
N Remarks: Did not result in the unplanned release that has the potential for groundwater, 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: Did not result in the failure of radioactive material packing.
Involved an emergency or non-emergency event or situation, related to the health and safety of the public or onsite 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 an ALERT declaration and report, the event had no impact on personnel / public health and safety nor protection of the environment.
7 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 issue is well understood and does not involve safeguards.
Failure of license significant safety related equipment or adverse impact on licensee operations as a result of a safeguards-initiated event (e.g., tampering).
N Remarks: The event was not tampering.
Actual intrusion into the protected area N
Remarks: 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: 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: Did not involve inadequate nuclear material control.
Confirmed tampering event involving significant safety or security equipment N
Remarks: The 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: 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: Did not involve nuclear material control and accounting.
8 Involved a significant safeguards infraction that demonstrates the ineffectiveness of facility security provisions.
N Remarks: Did not involve safeguards.
Confirmation of lost or stolen weapon.
N Remarks: Did not involve the loss of a weapon.
Unauthorized, actual non-accidental discharge of a weapon within the protected area.
N Remarks: Did not involve a weapon.
Substantial failure of the intrusion detection system (not weather related).
N Remarks: 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: Did not involve the package/Personnel search procedures.
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 conditions that tampering, or vandalism was not a factor in the condition(s) identified.
N Remarks: 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:
Based on the review of the event and the analysis, none of the deterministic or risk criteria were marked YES. An informational risk assessment was also performed and based on the risk <1E-06 CCDP, inspection remained in the baseline inspection region. Therefore, baseline inspection will be used to perform follow-up inspection of this issue.
BRANCH CHIEF REVIEW: Alan Blamey DIVISION DIRECTOR REVIEW: Mark Franke ADAMS ACCESSION NUMBER: ML24229A133 EVENT NOTIFICATION REPORT NUMBER (EN57270);
E-mail to NRR ReactiveInspection@NRC.GOV Signed by Blamey, Alan on 08/16/24 Stamm, Eric signing on behalf of Franke, Mark on 08/19/24
9