Licensing the High Burnup Research Cask Transportation Package – Lessons Learned

AUTHORS
John McEntire PMP, Donald McGee PMP, and Sven Bader PhD
Orano Federal Services

PRESENTING
March 12, 2025
Waste Management Symposia

ABSTRACT
Obtaining a Certificate of Compliance (CoC) issued by the U.S. Nuclear Regulatory Commission (NRC) for the High Burnup Research Cask (“the Cask”) transportation package presented unique challenges. In accordance with 10 CFR Part 71, Orano implemented an innovative approach to satisfy the regulatory requirements and obtain the CoC. The Cask is an Orano TN Americas TN-32B vertical dry storage system with a modified closure lid allowing for the insertion of thermocouples to measure temperature at predetermined locations from within the cask loaded with used fuel. The Cask contains thirty-two high burnup (HBU) used fuel assemblies that were selected specifically for conducting research to understand aging mechanisms and behavior of HBU used fuel during dry storage conditions. After about a 10-year storage period, the Cask with its contents will be shipped to a U.S. fuel examination facility to be opened while remaining dry, allowing the used fuel to be extracted and comparative analyses to be conducted against “sibling” donor used fuel pins, which are representative of the used fuel loaded in the Cask and established a baseline for analyses. Future analyses of the HBU used fuel loaded in the Cask will provide data to support regulations and guidance for HBU used fuel aging management programs and inform stakeholders on the continued safe interim and long-term storage, transportation, and disposal options for this fuel.

Several design enhancements were incorporated prior to loading the Cask with HBU used fuel to prepare it for a future shipment without having to potentially re-open before shipping. While these enhancements helped resolve most transport licensing concerns with the original cask design, not all challenges could have been anticipated without beginning the detailed analyses and presenting the licensing approach for this package with its unique modifications to the NRC reviewers. Orano began transport licensing activities immediately following the loading of the Cask in November 2017. During development of the package design and licensing approach, several challenges presented themselves to Orano, including selection of impact absorber material and consideration of use of the installed thermocouples beyond the future transport. Addressing these challenges resulted in identifying special tests needed to demonstrate the thermocouple lance containment function during hypothetical accident conditions of transport. Other challenges in project management occurred during the work, including the onset of the COVID-19 pandemic and the need for prioritizing other transport package reviews for licensing by the NRC in parallel with the Cask licensing. The initial application was completed and transmitted to the NRC for acceptance review in August 2021. The NRC’s detailed application review began in October 2021 and Orano received a CoC for transport in July 2024.

Transporting the Cask in the 2027 timeframe is extremely important to ensure that continued storage license commitments (i.e., tollgates) are achieved. The first commitments are due in April 2028, when both Xcel Energy’s Prairie Island Nuclear Generating Plant and Constellation’s Calvert Cliffs Nuclear Power Plant rely on the initial data from the Cask to be granted a storage license extension. This same commitment was subsequently extended to all commercial nuclear facilities across the U.S.

INTRODUCTION

This paper presents a discussion of lessons learned from the task of licensing the High Burnup Research Cask (“the Cask”) transportation package under 10 CFR Part 71. The Cask was designed by Orano TN Americas to be a dual-purpose storage and transportation system. To date, only the generic TN-32 along with its variants TN-32A and TN-32B have been licensed by the U.S. NRC under 10 CFR Part 72 for storage of used nuclear fuel (UNF). The Cask is the TN-32B variant which is identical to the TN-32 except that the upper lift trunnions are designed as single-failure proof. The Cask was modified specifically to conduct research on high burnup (HBU) UNF.

A major modification relevant to both storage and transportation functions was made to the Cask’s primary closure lid to allow the insertion of seven thermocouple lances into the fuel basket to measure fuel temperatures while the Cask is in the storage mode in a vertical configuration, which is expected to last roughly 10 years before preparing to transport the Cask. Figure 1, below, provides an image of the modifications done to the Cask’s primary closure lid.

Figure 1 – Cask Primary Lid Modifications – Courtesy, Orano

Due to this modification, a unique transportation license application was required in lieu of a generic application for the TN-32 family of casks. Shortly after the Cask was placed into storage at Dominion Energy’s North Anna Power Station under a site-specific storage license, the project team began work to prepare for licensing the Cask for transportation, which included developing a licensing plan and having early, pre-application discussions with the Regulator to ensure an efficient and consistent approach to licensing. Some pre-work, including bounding analyses for transportation and physical changes to the Cask to prepare for future transportation, had already been performed before UNF loading. The purpose of this early work was to give the project team confidence in the overall approach to transport licensing and to make the Cask more “transportable” so that fewer steps would be needed to prepare the Cask for transport. Additionally, the primary closure lid’s bolts were upgraded to meet more stringent transport requirements and impact limiter bracket bars were installed on the Cask’s outer body to assist with installation of impact limiters. To comply with ANSI N14.5-2014 leakage requirements for a UNF transportation package, a special, “best effort” leakage rate test was conducted prior to UNF loading to provide confidence that the prefabricated Cask would perform to those requirements. This leakage rate test was not performed, nor was it required at the time of original fabrication, but was imposed on the Cask to meet requirements for UNF transportation licensing. And lastly, all the UNF loaded in the Cask was pre-examined to avoid loading any failed fuel.

BACKGROUND

Orano TN Americas had previously obtained both storage and transportation licenses for the dual purpose TN-40 family of casks which has many similarities with the TN-32. Therefore, the Cask had a starting point for many of the required analyses, including benchmark scale drop and impact testing, to aid in transportation licensing. New models were required to be developed to analyze the Cask with the modified closure lid for all hypothetical accident condition scenarios as required by regulation. During the course of developing the packaging design and analyzing the Cask for both normal and accident conditions of transport, the package design evolved over time in areas such as structural performance to strengthen the package against puncture through the modified primary lid, and new tests were identified and conducted to qualify the thermocouple lances to perform a containment function. Material selection of impact limiter absorbers was also evaluated to save on project cost, but due to the benchmark tests conducted for the TN-40, it was decided that the same material would be used so that additional tests would be avoided.

Design, engineering, and new tests leading to development of the initial transport licensing application submittal took nearly three years for the project team to accomplish the work. Both the Regulator’s review and the project team’s responses to the Regulator’s requests for additional information led to an additional three years to complete licensing to receive the Certificate of Conformance (CoC). During that time both the project team and Regulators had to navigate through the COVID-19 worldwide pandemic and prioritize with other transportation licensing applications for review with varied levels of importance due to active customer and strategic business needs.

After the storage period, the Cask is planned to be transported to a U.S. fuel examination facility with a hot cell to allow opening and extraction of the stored UNF in a dry environment. From there, fuel pins will be extracted from select assemblies to undergo confirmatory fuel examinations and testing against the baseline fuel pins (sibling fuel pins). The purpose of these examinations and tests, which may consist of both non-destructive and destructive examination methods, is to identify any changes in the properties of the fuel during the dry storage period. This will aid the nuclear industry to understand aging mechanisms and behavior to support regulations and guidance for HBU used fuel aging management programs and inform stakeholders on the continued safe interim and long-term storage, transportation, and disposal options for this fuel.

However, timing of the planned transportation is crucial to meet ongoing regulatory licensing commitments imposed by the Regulator as part of the Aging Management Plan for continued plant operation. Independent Spent Fuel Storage Installation (ISFSI) license renewals for Xcel Energy’s Prairie Island Nuclear Generating Plant and Constellation’s Calvert Cliffs Nuclear Power Plant have the earliest “Toll Gate” dates, coming due on April 4, 2028, and April 30, 2028, respectively. Further Toll Gate commitments for these two Utilities occur in April 2038, which would require the loaded UNF to have been analyzed and compared against the sibling fuel pins.

PRE-TRANSPORTATION LICENSING WORK

One of the first technical challenges was being able to permit the Demonstration Cask with its modifications to be licensed to load used nuclear fuel at an operating nuclear site under a 10 CFR Part 72 storage license. With assistance provided by Orano, Dominion Energy sought an amendment to the North Anna Power Station’s site-specific storage license to include the Cask. The amendment was approved in September 2017 and the Demonstration Cask was subsequently loaded and placed into storage in November 2017.

During the storage license period, a set of bounding analyses for transportation were conducted to ensure that any upgrades needed to the Cask were incorporated in the site-specific storage license. Based on the results of a bounding structural evaluation, higher strength lid bolts with reduced shank diameter and hardened washers were changed in the design. The primary closure lid’s bolts/thru holes were increased in diameter, and so with the reduced bolt shank diameter, allows prevention of lateral lid movement from contacting the lid bolts during a postulated side or near horizontal impacts during free drops. Other structural evaluations for the Cask and basket were conducted to provide high confidence against drop scenarios. The Cask was evaluated for a 30-foot inverted end drop with impact limiters to ensure the containment integrity, and the basket’s structural adequacy was evaluated for a postulated side drop event against a conservative drop load. A shielding calculation determined that external radiation dose rates did not meet the definition for an exclusive use transport and made recommendations on material thicknesses and use of a personnel barrier.

To aid in the attachment of the impact limiters, sixteen bracket bars were installed on the Cask’s outer body prior to loading. This would help achieve ALARA goals to avoid worker dose performing the installation while the Cask is loaded. Figure 2, below, provides an image of two sets of installed bracket bars.

Figure 2 – Installed Impact Limiter Bracket Bars – Courtesy, Orano

To comply with ANSI Standard N14.5-2014, Orano proposed to perform a “best effort” fabrication leakage rate test of the metallic containment boundary, which was accepted by the NRC. This test was not previously performed during original fabrication because it was not a requirement at the time. The test method followed recommendations provided in Evacuated Envelope – Gas Detector per Section A.5.4 of the Standard. To achieve initial conditions for the test, the cavity was filled with pure helium and the annulus between the gamma shield and containment boundary were accessed by two drilled holes at a weld joint for the shell flange to gamma shield, 180 degrees apart. These holes allowed for connections to be made to the leak detector and standard leak. The only limitations to this method where that there were no means to determine conductance on any part of the body of the containment boundary (inner shell and bottom inner plate) and no means to clean the annulus to eliminate out-gassing under high vacuum conditions. Note that the inner shell was shrunk-fit into the shield shell during installation, so the annulus gap thickness (void space) could not be determined. Figure 3, below, shows an illustration of the containment boundary leakage test that was performed.

Figure 3 – Containment Boundary Leakage Rate Test Setup – Courtesy, Orano

To ensure the best test results, the cavity was vacuum conditioned for 19 days. Three accumulation tests of the annulus were performed. After two hours for all three tests, the leakage rates were less than 1.0 x 10-8 atm-cm3/sec indicating no leak path in the annulus that had conductance with the sensing port. Additional observations were identified to provide further confidence in the Cask’s leak tightness such as prior to opening for visual inspection before modification, the Cask was stored for thirteen years with pressurized helium gas in the cavity with no noticeable loss of pressure, and upon initial access to the annulus, no significant helium was detected. During the approximate 10-year storage period on the ISFSI, the Cask seals will be monitored for leakage and corrective action will be taken if a low pressure alarm is detected. Figure 4, below, provides an image of a borescope camera probe at one of the two drilled hole sites validating the breach access into the annulus. The dark vertical gap in the image represents the void pocket and spacing between two shims installed between the shell flange and gamma shield.

Figure 4 – Image of Borescope Camera Probe in Drilled Hole – Courtesy, Orano

It was decided during the Test Program development that the Cask would not be loaded with any failed fuel for the experiment. A detailed fuel selection report was developed early in the project to identify candidate UNF assemblies for research. After the fuel was selected, Dominion Energy conducted confirmatory visual scans of the fuel inside the pool.

TRANSPORTATION PACKAGE DESIGN & LICENSING

As previously mentioned, the project team developed a set of bounding analyses to provide assurance that the Cask with its modifications and pre-selected HBU payload would be licensable for transport. Package preliminary design activities began at the end of 2018. Since the TN-40 design already had a transportation CoC and the two cask designs were similar, the project had a reasonable starting point to model the calculations and analyses after. One of the first problems to solve was the issue of puncture resistance through the modified lid. Due to the inside diameters of the primary closure lid’s seven through-hole penetrations wells where the thermocouple lances are housed being greater than 6-inch and that the hypothetical accident condition calls for a 6-inch round puncture bar, the package design would require a new thick plate to rest on top of the primary closure lid for added puncture resistance. The condition was theoretical in analysis given any chance to align the puncture bar perfectly aligned with the penetration wells.

The interface between the “puncture resistant shield plate” and the primary closure lid was sandwiched plate-to-plate meaning no gap between the two plates. This meant that the thermocouple lances housed within the primary closure lid’s penetration wells would be rendered inoperable, requiring the electrical leads to be cut, the overpressure monitoring tubing to be cut, and smaller plates to be welded to the top of the penetration to abandon the thermocouples in place to not rely on them to perform a containment boundary function. During preliminary design development, stakeholders from the Electric Power Research Institute (EPRI), National Labs, and the U.S. Department of Energy (DOE) began requesting information on whether the thermocouple lances could be useable following transportation, allowing continued temperature measurements. A study was commissioned by Orano to investigate two methods: cut/splice the thermocouple leads or save/wrap. The study revealed that there was too much risk associated with the cut/splice method due to ALARA concerns and conditions were not ideal (i.e., not mimicking factory conditions) due to high temperatures and working at height. Save/wrap was pursued as the preferred method, and a plate design was chosen that would allow the electrical leads and tubing to remain intact during transportation. However, utilizing this solution would require qualifying the thermocouple lances as a containment boundary.

The thermocouple lances are not secured to the cask with traditional fasteners to tighten the seals. Instead, sealing force is made by tightening eight jacking screws with a backing plate against the thermocouple lance housing. The thermocouple lance housing does not make a tight lateral fit inside the penetration well, but rather there is approximately 0.75-inch of space for lateral movement so that the lance, when inserted into a fuel assembly guide tube, would not apply any bending stresses on the lance due to minor misalignments between the guide tube and penetration. Figure 5, below, shows an illustration of the thermocouple lance assembly with components needed to provide sealing force for performing the containment function. Note that the uppermost plate was an original concept but has since been replaced by a newer design.

Figure 5 – Thermocouple Lance Assembly – Courtesy, Orano

To demonstrate sealing tightness and maintaining containment after a side drop event under hypothetical accident conditions, a lateral slide test was conceived to calculate the required force to cause the thermocouple lance to move or slide across the sealing surface. The following contributed to the test setup, which is shown in the Figure 6 image, below:

1. Spare components identical to the installed components on the Cask were on hand to establish the material conditions.
   
   
2. The test rig was oriented in the horizontal direction to be in the transport configuration. To achieve maximum movement potential, the thermocouple lance housing was biased at the top of the penetration well.
   
   
3. Heating coils connected to a thermostat were used to adjust the operating temperature to the predicted temperature of the primary closure lid during normal conditions of transport.
   
   
4. A pipe was connected to the test rig to apply helium to mimic the cask’s internal helium pressure.
   
   
5. A leakage rate testing rig was connected to the overpressure tubing to measure leakage across the seal during the test. The leakage rate was measured as 2.3 x 10-12 atm-cm3/sec indicating a leak-tight seal.
   
   

Figure 6 – Thermocouple Lateral Slide Test Setup – Courtesy, Orano [1]

Load was applied to the side of the thermocouple lance housing until movement occurred, which was determined to be 0.65-inch. The seal failed due to the load not being perfectly perpendicular, causing seal scoring on one side. However, the force required to cause movement was measured as 48 kN (10.8 kips) which corresponded to about 1,000g. With a conservative dynamic load factor of 2, it would require 500g to cause lateral displacement, which is far greater than the predicted 50g impact from a hypothetical side drop from 9 m (30 feet). This result provided confidence that the thermocouple lance would perform its intended containment function and was therefore included in the license application. [1]

The project team scheduled its first in-person meeting with the NRC early in the preliminary design development to present the licensing approach, application schedule, design progress, and to solicit early feedback on the approach. Initially the impact limiter absorber material was planned to be foam as a cost-savings measure, but the NRC staff recommended to use wood to match the conditions of the TN-40 scale impact testing. This caused only a minor change to the design since detailed analyses had not yet been performed. It was agreed to establish periodic meetings to provide progress updates to the NRC Staff on design evolutions, analysis results, application submittal date changes, and any other significant impacts to the overall project schedule. One such change to the project schedule was an allowance to optionally transport the cask before the anticipated date of not sooner than July 1, 2027. Additional thermal analyses were conducted by Dominion Energy to calculate the loaded UNF’s decay heats at various intervals. Decay heat results for October 1, 2023, were selected to bound the earliest possible shipment date.

The initial design and safety analysis report (SAR) was completed and submitted to the NRC for acceptance review in August 2021. Shortly after in October 2021, the NRC informed Orano that its application contained enough detail to allow the NRC staff to begin its review without the need for supplemental information. The first request for additional information (RAI) was submitted to Orano in May 2022. Due to ongoing customer commitments, the Orano team had to divide RAI No. 1 into two separate parts: structural and non-structural. Also noteworthy to mention, the NRC staff commended the team for a thorough and complete discussion on criticality, resulting in a completed chapter with no additional information required. The non-structural RAI response was submitted in August 2022 and the structural response in June 2023. The structural models were required to be updated resulting in several calculation revisions and updates to the SAR. Additionally, some of the structural model updates were questioned by the NRC staff resulting in a second RAI issued in January 2024 requesting justifications to some of the modeling changes. The final RAI response was provided in May 2024, and in July 2024 the NRC issued to Orano the CoC for the Cask transportation package.

Other schedule challenges also presented themselves during design and licensing progression. With the onset of the COVID-19 pandemic in early 2020 disrupting normal business functions and working conditions for approximately three years, the Orano team had to change the way work was done through remote interactions both within the team and with the NRC staff, including periods of prolonged illnesses and quarantines. In addition to the pandemic, Orano was engaged with the same NRC review staff for other transport package licenses, including both existing package license renewals and new designs that are strategic to its business. Orano worked with the NRC to prioritize reviews based on timely renewal to meet business needs and customer shipping schedules. Given the uncertainty of the timeframe when the Cask was to be shipped, it was assigned a lower priority resulting in delays to complete NRC reviews. The re-prioritization also allowed Orano to adjust resources supporting the structural RAI responses. Timing of the structural RAI responses submittal aligned with completion of the higher priority reviews, so the interruption was opportunistic to focus on the structural modeling updates to address the RAIs.

Figure 7, below, provides an overview of the design and licensing schedule, showing relations between the planned versus actual major activities and other schedule impacts.

Figure 7 – Design & Licensing Significant Events Timeline

FUTURE WORK

To transport the Cask to a DOE selected research facility, numerous upfront planning and preparatory activities must be performed to ensure a safe and efficient route is identified, including detailed logistics planning and site preparations at the origin and receipt sites. Specific plans and procedures will be developed and implemented to prepare, load, and transport the Cask in compliance with all the applicable regulatory requirements. As part of the overall effort, coordination with stakeholders will be an essential element of the process. Safety and security plans and procedures will be developed to protect the staff, the public, and the Cask itself during all phases of transportation. Emergency response and preparedness will be established along with notification protocols to provide response guidance in the event of a reportable incident.

Significant fabrication works will be performed to support the transportation planned for 2027. It is anticipated that in the second quarter of 2025, most fabrication efforts will begin on the main components of the transportation package, which include:

• Impact limiters and tie rods, 15-month schedule.
  
  
• Transportation skid with end stops and personnel barrier, 12-month schedule.
  
  
• Puncture resistant shield plate and thermocouple lance cover plates, 6-month schedule.
  
  

One license amendment is anticipated for the Operations section of the SAR. Only one method was initially evaluated for placing the Cask into the horizontal configuration at the origin site. As transport planning activities and logistical issues at the origin site began to be worked, the project team now has ability to identify and assess alternative means to prepare the Cask for transport which may yield improvements to worker safety and dose control. The origin site’s safety basis is also being evaluated to include alternative methods to transfer UNF on site, including the use of a mobile crane with at least double the capacity of the highest expected handling weight.

To ensure that the Cask is handled and transported in a safe and compliant manner, the project team is planning to conduct a physical dry-run of the preparation for shipment activity at least six months prior to shipment using a spare, twin TN-32B cask owned by EPRI. It is identical to the Cask in every way except for the modifications done to the primary closure lid and is not presently licensed to store UNF. This will include a planned fit-up test of the impact limiters and puncture resistant shield plate, along with down-ending the spare cask into the transport skid and attachment of the end stops and personnel barrier for the purpose of mitigating risk of fit issues with the Cask. Any issues of fit will be resolved prior to prepping the Cask for shipment. [2]

CONCLUSIONS

The nuclear industry relies on lessons learned as a part of its culture of continuous improvement. The experience and knowledge gained during the licensing efforts for the High Burnup Research Cask should be an example for others in the steps needed to successfully plan and execute the methodology needed to obtain a transportation license for a UNF package. As always, working with regulators in a transparent approach is vital to resolving potential issues in an efficient manner. In addition, the licensing experience demonstrated that putting efforts into detailed upfront planning and anticipating technical challenges in advance and mitigation actions further increases the likelihood for a successful outcome in achieving the cost and schedule goals of the project. In summary, the following are key lessons learned:

• The importance of detailed upfront planning and sensitivity to react to stakeholder’s desired changes to the overall approach during performance is demonstrated as discussed in this paper.
  
  
• Working with the regulator in a transparent manner ensures ease of communication, consistent acknowledgement, and agreement with adjusted licensing approaches, including the benefits of improved cost and schedule efficiencies.
  
  
• Anticipating potential licensing challenges, taking early actions to mitigate concerns, and communicating with the regulator on how those challenges are being addressed provides the regulator with confidence in the project team’s licensing approach.

REFERENCES

1. K. Waldrop, “Transport License Approach to Maintain Thermocouples in High Burnup Research Project Cask,” presented at the 20th International Symposium on the Packaging and Transportation of Radioactive Materials, Juan-Les-Pins, France, June 11-15, 2023.
   
   
2. McEntire, “Full-Scale Dry Run to Prepare for Shipment of High Burnup Used Nuclear Fuel,” presented at the Waste Management 2024 Symposia 50th Anniversary, Phoenix, AZ, March 10-14, 2024.

ACKNOWLEDGEMENTS

Orano Federal Services wishes to thank EPRI and the DOE in partnering with Orano for continuing its efforts identifying solutions for the future transportation of UNF from commercial reactor sites across the United States. We also wish to thank Dominion Energy for their continued support of our project by hosting the Demonstration Cask at their North Anna Power Station since 2017 and working with us through planning for the first-ever shipment of a loaded dual-purpose cask from an operating nuclear energy station.

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