ML22259A121
| ML22259A121 | |
| Person / Time | |
|---|---|
| Issue date: | 09/08/2022 |
| From: | Kenneth Kolaczyk NRC/NRR/DRO/IRAB |
| To: | |
| Kenneth Kolaczyk, NRR/DRO/IRAB | |
| Shared Package | |
| ML22259A115 | List: |
| References | |
| Download: ML22259A121 (54) | |
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NIST Event Kevin Roche September 8, 2022
NIST Background Located on the NIST campus in Gaithersburg, MD Operated 24/7, Outage ~ 50 days Refueling is done blind Heavy-water-moderated-and-cooled HEU plate-type fuel with 34 plates per element and up to 30 elements in the core Non-pressurized heavy water primary cooling system with helium cover gas Carbon and HEPA filtered emergency exhaust ventilation and recirculation cleanup 3
Sequence of Events
- 0911 - Increasing radioactivity on fission product monitor
- 0912 - Increasing radioactivity on building exhaust stack monitor
- 0912 - Automatic shutdown due to high stack radiation level
- 0916 - NIST declared Alert in accordance with procedures
- 1532 - Event downgraded to Notification of Unusual Event
- 1935 - Event terminated
Element is out of position Approximately 3 inches above the top grid plate Damaged Element Top of Element should be flush with this surface Bottom view showing once molten material
Licensee Postulated Position of S-1175 (Model based on Initial View of the Top of the Element)
Licensee mock-up of the fuel element latching mechanism
Latching Video
As found condition, latched in the window
Inspection Report
- Sequence of Events Updated to include refueling and other activities that preceded the event
- Licensee Response Inspectors identified one follow-up item related to emergency planning
- Consequences of the Event Inspectors noted that DOE independent third-party assessment of radiological release determined that initial dose estimate of 0.5 mrem within 400-meter boundary is conservative Additional environmental samples confirm members of the public and the environment remain safe Inspectors identified two apparent violations related to exceeding fuel temperature safety limit
- Assess the adequacy of procedures Inspectors identified three apparent violations for inadequate fuel handling, startup, and emergency response procedures
Inspection Report
- Root and Contributing Cause Assessment NIST identified seven (7) root causes that contributed to the event Inspectors determined that the root causes analysis/discussion was incomplete Inspectors identified weakness in areas related to safety culture NIST submitted supplements to root and contributing cause assessments Inspectors determined that further assessment of the root cause and safety culture may be needed following the enforcement process
- Corrective Action Assessment NIST identified multiple corrective actions that will help to prevent recurrence Because inspectors determined the licensees root cause was incomplete, additional corrective actions may be required following the enforcement process Inspectors determined that further assessment of the details, implementation, effectiveness, and sustainability of the licensees corrective actions will be needed
Summary of Apparent Violations
- AV#1: Violation of Technical Specification 2.1, Safety Limit
- AV#2: Violation of Technical Specification 3.1.3, Core Configuration
- AV#3: Inadequate Refueling Procedure
- AV#4: Inadequate Startup Procedure
- AV#5: Inadequate Emergency Response Procedure
- AV#6: Violation of Technical Specification 3.9.2.1, Fuel Handling, Within the Reactor Vessel
- AV#7: Violation of 10 CFR 50.59(c)(1)
ADR Process
- Mediation lasted 22 hours2.546296e-4 days <br />0.00611 hours <br />3.637566e-5 weeks <br />8.371e-6 months <br /> (not including preparation and documentation), twice as long as usual for sessions covering violations
- Results of the NIST/NRC mediation were used to prepare the confirmatory order (CO).
- Mediation included NIST waiving its rights to a hearing on the order.
Summary of Follow-up Items Emergency response equipment issues that delayed the licensee response Abnormal primary system contamination Shutdown cooling pump failure Material control and accounting procedures including damaged fuel element Inadequate training - Operator licensing and requalification issues Design of the latching mechanism and/or controls in place to ensure elements can be properly latched.
NIST will investigate tools capable of providing early detection of off-normal NI behavior Procedure changes and associated 50.59 screens Ineffective Corrective Action Program Sustainability of licensees corrective actions Safety culture weaknesses Ineffective responses to Safety Assessment Committee (3rd party) audits Inadequate leadership responsibility
CO Outline Describes NISTs completed Corrective Actions Training revisions Procedure revisions Development of staffing plans Started development of a more robust Problem Identification and Resolution (PI&R) program Describes NIST benchmarking at similar facilities Describes additional funding NIST has secured to support recovery Specifies NIST Communications to NCNR personnel NIST will hire a 3rd party nuclear safety culture consultant within 6 months NIST will hire a 3rd party consultant within 12 months to review:
The revised PI&R program The Root Cause Analysis resulting from the Feb. 3, 2021 event NISTs revised training programs NISTs Revised procedures Safety Assessment Committee/Safety Evaluation Committee oversight NIST will implement the revised PI&R program in September of 2022, with tiered implementation through March of 2023
CO Outline (cont)
- Revise the employee concerns program within 6 months
- Develop a safety culture monitoring program within 9 months
- Conduct training on latching and fuel movement prior to any restart and update the requalification plan to specifically include requalification training
- Continue to update procedures and guidelines for procedural use and adherence
- Continue to benchmark other facilities
- Present at industry conferences
- Develop an employee engagement/rewards program within 6 months
CO Outline (cont)
- Conduct leadership training on safety culture and include in leadership appraisal process
- Assess the reliance on administrative controls for fuel operations
- Update reactor instruments to monitor and alert operators of abnormalities (condition-based monitoring)
- Assess configuration management system and incorporation with the PI&R program
Supplemental Inspections
- Supplemental Inspection Plan - August 1, 2022
- First onsite inspection is ongoing this week
- NRC inspections planned to: (1) inform the restart decision, (2) address SI violations and inspector follow-up items, (3) review implementation of CO items, and (4) confirm technical information from the technical review
- Supplemental inspections + routine inspections =
increased oversight of NIST operations
Supplemental Inspections Emergency planning / emergency response Safety Culture Refueling / fuel handling procedures Reactor startup procedures Operator training and requalification program; supervisor training Review disposition of Safety Advisory Committee recommendations Confirm consideration of CO2 build up potential Review corrective actions to address other equip failure (#2 shutdown pump)
Review refueling tool wear and replacement program Evaluate program to ensure expectations, processes, and procedures are in place to identify and implement safety improvements
NRC Approach to NIST Restart Decision Josh Borromeo, Branch Chief Non-Power Production and Utilization Facility Licensing
Root Causes and Corrective Actions License Review Enforcement Inspection Fuel Latching Event Safety Culture Design Changes Licensing Procedures Training NRC staff is addressing immediate and underlying causes to ensure sustainable corrective actions and prevent potential events.
Potential Events If underlying issues unaddressed Fuel Latching
Restart Decision The NRCs restart decision will be based on the following:
- ensuring that the event and the reasons that it occurred are fully understood
- confirming that NIST has adequately identified and addressed the impacts to the reactor
- ensuring that NIST has made corrections to prevent this event and similar types of events from happening again The restart decision will be informed by several NRC activities, including a technical review, inspections, and enforcement actions.
Restart Decision Process Overview License Review Technical Review Special Inspection Team Technical Evaluation Report Special Inspection Report Begin Enforcement Process Issue Enforcement Actions -
ADR and Confirmatory Order Root Cause &
Corrective Actions Restart Decision NIST Restart Request Develop and Perform Supplemental Inspection Plans Temporary Post-Restart Inspection Plan Post-Restart Inspection Activities to Monitor Performance Revised Corrective Actions License Review Enforcement Inspection
Technical Evaluation Report (TER)
The primary review area for the TER is the structures, systems, or components (SSCs) that could have been affected during the event.
Additionally, the TER will support the inspection activities to address causes that lead up to the event and the corrective actions necessary to resume operations.
Current TER Topics:
- Reactor Fuel
- Reactor Support Systems
- Reactor Vessel Internals
- Latching Process/Mechanism Review
- Design Basis Accident and Technical Specifications
Supplemental Inspections NIST selected alternative dispute resolution (ADR). The NRC staff will inspect the items outlined in the Confirmatory Order. These topics could include:
- Safety Culture
- Training
- Procedures Additional inspections related to the restart of the facility may be necessary to ensure its safe operation (e.g., restart procedures/plans).
Inspections will be necessary following restart to confirm sustainability of corrective actions (e.g.,
safety culture).
Milestones and Actions ADR is scheduled for May 10th
- Confirmatory Order follows Agreement in Principle from ADR License Amendment Request and TER target completion in May
- Dependent on quality and timeliness of NIST responses for information (e.g., revised procedures for latching)
NRC developing supplemental inspections. These are being informed by ADR and TER.
NIST developing responses to additional information needs for staff to complete TER and LAR review.
NIST is targeting the end of May to complete cleanup. The current focus areas are:
- Completion of the cleanup primary coolant system
- Completion of the evaluation and inspection of other fuel elements to determine if they can be reused
Restart Decision The timing for NRCs decision to restart the facility will be informed by the outcome of ADR, the necessary inspections prior to restart, and completion of the TER.
While the NRC is prioritizing the review, the agency will not authorize restart until it has determined that restart will be protective of public health and safety.
NIST Event
- Background
- SIT Charter Objectives
- Summary of the Report
- Summary of Apparent Violations
- Violation details
- Summary of Inspector Follow-up Items
- Current Status
Licensee Response
- Emergency Planning Response
- Placed reactor in safe, shutdown condition with cooling maintained
- Evacuated confinement building to control station in adjacent building
- Environmental monitoring performed at confinement exhaust stack and 400-meter emergency planning site boundary (within NIST Gaithersburg campus fence line)
- Environmental sampling for radioactive material releases, as well as radiological surveys, confirmed that release amounts were a small fraction of alert or notification of unusual event criteria, which led to event termination later that day
- Safety System Response
- Radiation monitors and safety systems performed as designed
Fuel Element S-1175 Lower Grid Plate
- S-1175 nozzle resting on lower grid plate
- Once-molten material on lower grid plate S-1175 nozzle
- S-1175 in close proximity to adjacent fuel element in position H-7 and I-6 J-7 Inlet Nozzle Element in position H-7 Element J-7 Once-molten Material
Fuel Element S-1175 Lower Grid Plate
- As referenced to the nozzle diameter (2.4 inches), once-molten material was estimated at 1 inch by 2 inches.
- No indications of visible damage to outer support plates Lower Gridplate J-7 Inlet Nozzle 2
Key Messages
- NIST Test Reactor remains safely shutdown
- Radiation release was a small fraction of regulatory limits
- Samples continue to indicate no detectable environmental impact
- NRC approval is required for restart
- Inspectors identified 7 Apparent Violations
- Inspectors identified weaknesses in NIST Root Cause Reports
- Additional assessment of NIST Corrective Actions is required
- SIT open items will inform supplemental inspection/future oversight activities (under development).
Introduction
- Background - short description of the NIST facility
- heavy-water-moderated-and-cooled, enriched-fuel, tank-type reactor
- Event Description - abbreviated description of February 3 event
- NRC Response - outline inspection activities/responsibilities
Event Consequences
- Public Dose Consequences
- Less than 0.5 mrem
- standard chest x-ray is about 10 mrem
- regulatory limit is 100 mrem/year
- Based on building exhaust stack air samples
- Releases of Xe-133, Xe-135, and Cs-138 were small fractions of regulatory limits (10 CFR Part 20, Appendix B, Table 2)
- NRC staff verified by performing confirmatory calculations
- Occupational Dose Consequences
Event Consequences
- Environmental Consequences
- Real-time monitoring during event showed dose levels at boundaries to unrestricted areas (NIST Gaithersburg Campus fence lines) remained constant, consistent with normal environmental background radiation levels
- Soil and water sample results showed no detectable impact to the sampled environment that occurred as a result of the event Sample image showing GammaTracer monitoring device
Event Consequences
- Facility Consequences -
Exceeded Fuel Temp Safety Limit (842 °F)
- Observed one element not fully seated in normal position
- Observed small amount of once molten material on lower grid plate
- Cladding would melt if temperatures reached 1076°F
- 1202°F (580°C - 650°C)
RK1
Slide 37 RK1 Signficant operational event for facility. Event perspective facility design, barriers, help to ensure the consequences are not signficant.
Roche, Kevin, 4/14/2021
Event Consequences
- Facility Consequences - Exceeded Fuel Temp Safety Limit
- Based on all available information to date, inspectors preliminarily determined that the fuel temperature safety limit was exceeded resulting in fuel plate damage (i.e., blistering, cracking, and melting) in the element.
SW1
Slide 38 SW1 A NIST fuel element is made up of fuel plates, curved and flat unfueled plates, and upper and lower cast pieces (i.e., handling and nozzle adapters). Each element has an upper section and a lower section, with seventeen (17) fuel plates per section for a total of thirty four (34) fuel plates. Each fuel plate is approximately 13 inches in length by 2.7 inches in width by 0.05 inches in thickness (33 cm length by 7 cm width by 0.13 cm thick). The two sections are separated by a 7-inch (17.78-cm) gap (i.e., a volume without fuel plates).
The NIST test reactor core consists of 30 fuel elements that are held in position by upper and lower grid plates.
Schuster, William, 4/14/2021
Core Inspection - Reference Core Map Element of Interest, SN# S-1175
Core Inspection - Second In-Core Plan NIST Core consists of 30 HEU fuel elements Cladding and fuel support plates are Aluminum 6061 Melting point of Al 6061 is 580-650 C (1085 - 1202 F)
Technical Specification Safety Limit is 450 C (840 F)
J-7 I-6 K-6 H-7
Core Inspection - Second In-Core Plan Licensee using remote camera equipment to visually inspect the elements.
Different picture angles of element J-7 via the refuel and V3 core access ports.
First 2 photos 3rd photo J-7
Element J-7 As Found Condition View of J-7 from access port V-3 (opposite side)
More once-molten material near J-7 nozzle Licensee plans on performing more inspections to further characterize the condition of element 1175 and adjacent elements J-7 Inlet Nozzle Lower Gridplate
SIT Charter Objectives Develop the sequence of events related to the event.
Evaluate the licensee's response to the event, including assumptions and calculations.
Assess the consequences of the event.
Assess the adequacy of facility procedures for special nuclear material accounting, receipt, and inspection, and procedures for fueling and defueling operations.
Review any related maintenance and/or outage actions that could have contributed to the event.
Assess the licensee's determination of the root cause of the event.
Assess the licensees completed and planned corrective actions to ensure all deficiencies associated with the event are adequately addressed and the corrective actions will prevent recurrence.
- Specification - The reactor fuel cladding temperature shall not exceed 842°F (450°C) for any operating conditions of power and flow.
- The fuel temperature safety limit is set to maintain the integrity of the aluminum fuel cladding, which requires that the cladding remain below the blistering temperature of 842°F (450°C)
- The aluminum alloy used for fuel cladding would melt if temperatures reached a range of 1076°F - 1202°F (580°C - 650°C).
AV #2 TS 3.1.3, Core Configuration
- Specification - The reactor shall not operate unless all grid positions are filled with full length fuel elements or thimbles, except during subcritical and critical startup testing with natural convection flow.
- Core grid positions shall be filled to prevent coolant flow from bypassing the fuel elements for operation of the reactor with forced coolant flow.
- The reactor was operated with a fuel element misaligned in grid position J-7 which prevented cooling flow through the element.
- This misalignment was observed during the remote visual inspection activities of the reactor core.
AV #3 TS 6.4, Procedures (Refueling)
- Specification - written procedures shall be prepared, reviewed and approved prior to initiating activities such as:
(1) startup, operation, and shutdown of the reactor (2) fuel loading, unloading, and fuel movement within the reactor vessel (3) surveillance checks, calibrations, inspections and maintenance of equipment required by the technical specifications that may have an effect reactor safety (4) implementation of required plans such as emergency or security plans
- Specifically, the procedure instructed the operators to ensure the mark on the latching tool lined up with the mark on the index plate placed on the reactor top and no such mark existed
- The procedure for fuel loading activities that was not suitable for the circumstances and did not contain necessary information to ensure the fuel elements were latched prior to startup
AV #4 TS 6.4, Procedures (Startup)
- Specification - written procedures shall be prepared, reviewed and approved prior to initiating activities such as:
(1) startup, operation, and shutdown of the reactor (2) fuel loading, unloading, and fuel movement within the reactor vessel (3) surveillance checks, calibrations, inspections and maintenance of equipment required by the technical specifications that may have an effect reactor safety (4) implementation of required plans such as emergency or security plans Procedure(s) for reactor startup activities were not suitable for the circumstances and did not contain necessary guidance for the operators on what to look for during startup, what constitutes abnormal oscillations, and potential causes.
The reactor startup procedure, OI 1.1, Reactor Startup, states that operators should monitor for abnormal fluctuations or oscillations on nuclear channel indications.
Does not provide amplifying guidance for operators to use when making the abnormal determination.
AV #5 TS 6.4, Procedures (Emergency Reponses)
- Specification - written procedures shall be prepared, reviewed and approved prior to initiating activities such as:
(1) startup, operation, and shutdown of the reactor (2) fuel loading, unloading, and fuel movement within the reactor vessel (3) surveillance checks, calibrations, inspections and maintenance of equipment required by the technical specifications that may have an effect reactor safety (4) implementation of required plans such as emergency or security plans
- Procedure(s) for implementation of required emergency plans that were not suitable for the circumstances.
- Did not provide sufficient effluent sample guidance to ensure a timely response
- Did not specify how to reoccupy the building following evacuation (CO2 hazard existed)
AV #6 TS 3.9.2.1, Fuel Handling, Within the Reactor Vessel Specification - Following handling of fuel within the reactor vessel, the reactor shall not be operated until all fuel elements that have been handled are inspected to determine that they are locked in their proper positions in the core grid structure; and, that this shall be accomplished by one of the following methods:
- (1) elevation check of the fuel element with main pump flow,
- (2) rotational check of the element head in the latching direction only, or
- (3) visual inspection of the fuel element head or latching bar NIST operators failed to implement any of the specified methods.
- Requirement - A licensee may make changes to a facility without obtaining a license amendment only if a change to the technical specifications is not required.
- NIST made changes to the refueling tooling that invalidated the capability of operators to verify that a fuel element was adequately latched as specified in TS 3.9.2.1(1).
Next Week:
Prairie Island Emergency Diesel Generator Issues and RICT Implementation