ML25077A286
| ML25077A286 | |
| Person / Time | |
|---|---|
| Site: | Grand Gulf  (DPR-046) |
| Issue date: | 03/18/2025 |
| From: | Douglas Dodson NRC/RGN-IV/DORS/PBC |
| To: | John Monninger Region 4 Administrator |
| Shared Package | |
| ML25073A052 | List: |
| References | |
| Download: ML25077A286 (1) | |
Text
OFFICIAL USE ONLY - SECURITY RELATED INFORMATION J. Monninger 2
OFFICIAL USE ONLY - SECURITY RELATED INFORMATION March 18, 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 GRAND GULF NUCLEAR STATION MANUAL SCRAM INITIATION ON FEBRUARY 15, 2025 Pursuant to Regional Office Policy Guide 0801, 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 Grand Gulf Nuclear Stations manual reactor scram from degrading condenser vacuum and subsequent impacts on safety-related electrical loads. 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 baseline inspection be performed for follow-up of this event.
The evaluation also documents the staffs determination that no special inspection will be conducted for impacts to the sites security systems resulting from the manual scram. The staff reviewed the impacts to security and determined that none of the security deterministic criteria were met. The basis for this determination will be documented in a separate non-public enclosure to this memo.
CONTACT: Douglas E. Dodson II, DORS/PBC (817) 200-1148 Jesse M. Rollins, DRSS/PSB (817) 200-1527 Signed by Miller, Geoffrey on 03/17/25 Signed by Dodson, Douglas on 03/13/25
OFFICIAL USE ONLY - SECURITY RELATED INFORMATION J. Monninger 2
OFFICIAL USE ONLY - SECURITY RELATED INFORMATION Concur with Recommendation:
John D. Monninger Date Regional Administrator
Enclosures:
1.
MD 8.3 Decision Documentation Form (Deterministic and Risk Criteria Analyzed) 2.
Security-Related MD 8.3 Decision Documentation Form (Security-Related Deterministic Criteria Analyzed) transmitted herewith contains SUNSI. When separated from Enclosure 2, this transmittal document and Enclosure 1 is decontrolled.
Signed by Monninger, John on 03/18/25
ML25077A286 (Cover letter w/ Enclosure 1)
Non-Public Designation Category: MD 3.4 Non-Public A.3 ADAMS ACCESSION NUMBER: ML25072A161 (Cover letter w/ Enclosure 1 & 2)
Cover Letter w/ Enclosure 1:
SUNSI Review By: JMR Non-Sensitive Sensitive Publicly Available Non-Publicly Available Cover Letter w/ Enclosure 1
& 2:
SUNSI Review By: JMR Non-Sensitive Sensitive Publicly Available Non-Publicly Available OFFICE SRA:DORS BC:DRSS:PSB BC:DORS:PBC D:DRSS D:DORS RA:RIV NAME CYoung JRollins DDodson JGroom GMiller JMonninger SIGNATURE
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DATE 03/13/25 03/13/25 03/13/25 03/14/25 03/17/25 03/18/25
OFFICIAL USE ONLY - SECURITY RELATED INFORMATION OFFICIAL USE ONLY - SECURITY RELATED INFORMATION MANAGEMENT DIRECTIVE 8.3 DECISION DOCUMENTATION FORM (Deterministic and Risk Criteria Analyzed)
PLANT:
Grand Gulf Nuclear Station EVENT DATE:
February 15, 2025 RESPONSIBLE BRANCH CHIEF:
Douglas Dodson EVALUATION DATE:
February 19, 2025 BRIEF DESCRIPTION OF THE SIGNIFICANT OPERATIONAL EVENT OR DEGRADED CONDITION:
On February 15, 2025, at 10:40 p.m. local time, Grand Gulf Nuclear Station operators inserted a manual scram due to loss of condenser vacuum.
Rainwater collapsed a portion of a roof liner at a joint between the containment wall and the enclosure building, and rainwater penetrated foam fire seals that separate the auxiliary (reactor) building from containment on the 189-ft and 166-ft elevations. The rainwater ran down the containment wall on several levels and entered a Division-II engineered safety feature (ESF) switchgear room on the 139-ft elevation, shorting a 4160V-to-480V transformer in the 16BB2 load center. The rainwater breached secondary containment and multiple layers of secondary containment/fire zones: Fire Zone 1-A308 (16-BB2 & 16-BB4), Fire Zone 1-A316 (four divisions of reactor protection system at 139), Fire Zone 1-A417 (open area with safety related cables), and Fire Zone 1-A519 (open area with safety related cabling).
The transformer shorting caused the breaker supplying the 16BB2 and 16BB4 load centers from the Division-II ESF bus to open to protect the remainder of the Division-II ESF bus. The loss of the 16BB2 and 16BB4 load centers created a loss of power in Division-II ESF motor control centers (MCCs) 16B21, 16B41, and 16B42.
One of the loads on 16B42 is a balance of plant inverter that supplies power to the main turbine gland seal steam controller. The loss of power to the gland seal steam contributed to the loss of condenser vacuum, which necessitated a manual scram per off-normal emergency procedures.
Other mitigating systems loads that were impacted included Division-II drywell cooling; the Division-II emergency diesel jacket water pump; Division-II ESF switchgear coolers; secondary containment isolation valves such as the P44-F054, standby service water to plant service water crosstie valve; P44-F067B, plant service water crosstie valve to standby service water; and E30-F001B and F002B, suppression pool makeup valves.
Security-related impacts from the event are discussed in Enclosure 2.
On February 17, 2025, at 2:37 am local time, the Grand Gulf Nuclear Station entered cold shutdown (Mode 4).
OFFICIAL USE ONLY - SECURITY RELATED INFORMATION OFFICIAL USE ONLY - SECURITY RELATED INFORMATION Y/N DETERMINISTIC CRITERIA Involved operations that exceeded, or were not included in, the design bases of the facility N
Remarks: Although Division-II equipment was impacted and became unavailable, the event under evaluation was within the design basis of the facility.
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 reactor scram and unavailability of multiple components from rainwater in-leakage was not a major deficiency in design, construction, or operation of the facility, and does 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 rainwater breached secondary containment and some secondary containment isolation valves lost power (for example: P44-F054, standby service water), based on available information at the time of this evaluation, there was not a significant loss of integrity of the fuel, the primary coolant pressure boundary, or the primary containment boundary. Therefore, there was not a loss of any barriers during this event.
Led to the loss of a safety function or multiple failures in systems used to mitigate an actual event Y
Remarks: Multiple failures in systems used to mitigate an actual event were adversely affected by the rainwater intrusion, and power losses included power to some drywell cooling, Division-II emergency diesel generator jacket water pump, ESF switchgear coolers, and other Division-II loads.
Involved possible adverse generic implications N
Remarks: Based on available information at the time of this evaluation, the loss of multiple Division-II ESF load centers and MCCs due to rainwater in-leakage does not represent adverse generic safety implications.
Involved significant unexpected system interactions Y
Remarks: The rainwater breached secondary containment and multiple layers of secondary containment/fire zones: Fire Zone 1-A308 (16-BB2 & 16-BB4), Fire Zone 1-A316 (four divisions of RPS at 139), Fire Zone 1-A417 (open area with safety related cables), and Fire Zone 1-A519 (open area with safety related cabling). The staff determined that the ability of rainwater to penetrate these fire zones were unexpected system interactions.
Additionally, the inspectors noted unexpected security-related impacts, as discussed in Enclosure 2.
N Involved repetitive failures or events involving safety-related equipment or deficiencies in operations 1-2
OFFICIAL USE ONLY - SECURITY RELATED INFORMATION OFFICIAL USE ONLY - SECURITY RELATED INFORMATION Y/N DETERMINISTIC CRITERIA Remarks: The staff did not identify similar failures or events at this facility and determined that this event is not repetitive in nature. Hence, the staff determined the event did not involve repetitive failures of safety-related equipment or deficiencies in operations.
Involved questions or concerns pertaining to licensee operational performance N
Remarks: Based on available information at the time of this evaluation, the staff determined that operators responded appropriately to the event.
REACTOR SAFETY Y/N IIT Deterministic Criteria Led to a Site Area Emergency N
Remarks: The event did not lead to any declared emergencies.
Exceeded a safety limit of the licensee's technical specifications N
Remarks: The event did not result in exceeding 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: The staff assessed that the manual SCRAM and associated system impacts were similar to other failures evaluated using the baseline inspection program, and 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. The staff also assessed that the circumstances did involve safeguards concerns, but as documented in Enclosure 2, the staff determined that investigation of the circumstances involving safeguards concerns would not best serve the needs and interests 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: The event did not involve a significant failure to implement emergency preparedness program; there were no known failures to classify, notify, or augment onsite personnel.
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OFFICIAL USE ONLY - SECURITY RELATED INFORMATION OFFICIAL USE ONLY - SECURITY RELATED INFORMATION 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: Based on available information at the time of this evaluation, the staff determined the event did not involve significant deficiencies in operational performance. The operators appropriately referenced off-normal emergency procedures to resolve the event.
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 significant radiological release of byproduct, source, or special nuclear material to unrestricted areas.
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 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, 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 that may have resulted 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: Although the circumstances involved security-related impacts, as discussed in Enclosure 2, the staff determined that the circumstances were not sufficiently complex, unique, not well enough understood, or involved characteristics the investigation of which would best serve the needs and interests of the Commission.
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OFFICIAL USE ONLY - SECURITY RELATED INFORMATION OFFICIAL USE ONLY - SECURITY RELATED INFORMATION 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 lead 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.
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/hr 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 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.
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 staff determined the event did not have the potential to lead to an exposure in excess of 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 staff determined that the event did not have the potential to lead to an unplanned occupational exposure.
N Led to unplanned changes in restricted area dose rates in excess of 20 rem per hour 1-5
OFFICIAL USE ONLY - SECURITY RELATED INFORMATION OFFICIAL USE ONLY - SECURITY RELATED INFORMATION Y/N SI Deterministic Criteria in an area where personnel were present or which is accessible to personnel Remarks: The event did not lead to unplanned changes in restricted area dose rates.
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 to an unrestricted area.
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 an unplanned release of radioactive liquid inside the restricted area.
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 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: While a 10 CFR 50.72 report was submitted associated with the SCRAM (event number (EN) 57551), the event did not involve 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 that caused significant heightened public or government concern.
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OFFICIAL USE ONLY - SECURITY RELATED INFORMATION OFFICIAL USE ONLY - SECURITY RELATED INFORMATION 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:
C. Young DATE: February 21, 2025 Brief description for the basis of the assessment (may include assumptions, calculations, references, peer review, or comparison with licensees results):
The analyst utilized the Grand Gulf SPAR model version 8.82 along with SAPHIRE version 8.2.11 to estimate the risk associated with this event. The following modeling assumptions were made:
- 1. The analyst assumed that the risk associated with this event would be best represented by conducting an initiating event assessment based on a Transient (i.e., reactor SCRAM) event.
- 2. The analyst assumed that the use of FLEX coping strategies should be credited.
- 3. The analyst reviewed the components powered from the affected load centers and MCCs and determined that the loss of power to the following components represented challenges to associated mitigating functions:
- a. P44-F054 - Standby Service Water (SSW) to Plant Service Water (PSW) crosstie
- b. P44-F067B - PSW crosstie to SSW
- c. E30-F001B and F002B - Suppression Pool Makeup valves
- 4. The Division-II emergency diesel generator (EDG) was in a maintenance condition and was unavailable to perform its required safety function during the event.
The following modeling approach was performed to reflect the above assumptions:
- 1. Using the Events and Conditions Assessment (ECA) workspace, the initiating event frequency of the TRANS event was set to 1.0, while all other initiating event frequencies were set to zero to determine the CCDP associated with the event.
- 2. To apply credit for FLEX strategies, the basic event FLX-XHE-XE-ELAP (Operators Fail to Declare ELAP When Beneficial) was set to a probability of 1.0 E-2.
- 3. The following basic events were set to TRUE in the ECA workspace to represent the impact to mitigating functions associated with the affected components listed above:
- c. SPM-MOV-CC-F001B (Drain Valve F001B Fails to Open)
- d. SPM-MOV-CC-F002B (Drain Valve F002B Fails to Open)
- 4. The basic event EPS-DGN-TM-DGB (DG B is Unavailable Because of Maintenance) was set to TRUE, while all other nominal testing and maintenance basic events were set to zero.
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OFFICIAL USE ONLY - SECURITY RELATED INFORMATION OFFICIAL USE ONLY - SECURITY RELATED INFORMATION CONDITIONAL RISK ASSESSMENT The analyst quantified the SPAR model using the above modeling approach to obtain a total estimated conditional core damage probability (CCDP) of 7.87 E-7. Licensee risk analysis results for this event have not been evaluated.
THE ESTIMATED CONDITIONAL CORE DAMAGE PROBABILITY (CCDP) IS: 7.87 E-7 WHICH PLACES THE RISK IN THE RANGE OF:
No Additional 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:
The branch recommends baseline inspection follow-up. The SCRAM was not complex, and while the rainwater intrusion and subsequent power losses directly led to multiple Division-II safety-related systems becoming non-functional, the apparent scope of the impacts is understood and appears to be limited to one division of safety related equipment.
Additionally, the licensee has taken action to replace the transformer impacted by rainwater and interim actions to correct conditions resulting in roof leakage. Finally, in consideration of the expected risk significance, follow-up of issues associated with this SCRAM event, impacted systems, and fire zone/secondary containment boundaries can be assessed using baseline inspection procedures and is most appropriate.
Impacts to security-related systems are evaluated in Enclosure 2.
BRANCH CHIEF REVIEW:
Douglas E. Dodson II DATE:
March 13, 2025 DIVISION DIRECTOR REVIEW:
Geoffrey B. Miller DATE:
March 17, 2025 ADAMS ACCESSION NUMBER: ML25077A286 EVENT NOTIFICATION REPORT NUMBER (as applicable): EN 57551 E-mail to NRR_Reactive_Inspection@nrc.gov 1-8