North American Member News June 2021

ORNL performed an Assessment of Existing Transportation Packages for Use with HALEU (ORNL 2020 report), a link to which was provided in the Member News for May 2021, which assessed the potential to use currently licensed transportation packages for the transportation of HALEU by evaluating a representative package for each uranium fuel form category (for example, oxide and/or metal in fuel assemblies, fuel pins, powder, pellets, and uranium hexafluoride (UF₆).) The ORNL May 2021 report expands on the UF₆ analysis.  The ORNL 2020 report on UF₆ transport evaluated the DN-30 package. The study described in ORNL May 2021 report extends the work done in the ORNL 2020 report.

The ORNL May 2021 report’s assessment analyzed arrays at certain ²³⁵U enrichments under hypothetical accident conditions. Arrays considered include a 7 × 2 array of cylinders with 5.8 weight percent (w/o) ²³⁵U, a 3 × 2 array of cylinders with 6.7 w/o ²³⁵U, 1 × 2 array of cylinders with 9.5 w/o ²³⁵U, and a 1 × 1 array with 12.5 w/o ²³⁵U. This analysis considers fully reflected single cylinders, with and without a generic overpack, infinite arrays, and finite arrays with enrichments ranging from 6 to 20 w/o.  Based on the results documented in this report, 30B cylinders with UF₆ enriched up to 10 w/o ²³⁵U are expected to be able to be proven safe to store and ship with some configuration control.

Regulatory Considerations:

The ORNL May 2021 report notes that it does not address how an increase in the allowed UF₆ enrichment affects compliance with transportation regulations. It only addresses those requirements related to the proof of criticality safety for transport found in 10 CFR Part 72, Packaging and Transportation of Radioactive Material.  It notes that, in general “10 CFR 71.55 addresses the subcriticality of a single package, and it describes the conditions and configurations that must be considered. Once such condition is that a package must remain subcritical if water leaks into the containment system (b). This section also includes an exception (g) to this requirement for UF6 having an enrichment of up to 5 wt.% (under certain conditions). This study assumes that this exception will be extended for UF6 in the HALEU range of enrichments.”

[1] GAIN’s primary objective is to provide the nuclear industry and entrepreneurs with a single point of access to the national laboratory system and its expertise and research tools.

In its conclusions, ORNL notes that the scope of the study was limited to the investigation of the feasibility of using existing 30B cylinders for the storage and transportation of LEU+ (5-10 w/o ²³⁵U and HALEU (10-20 w/o ²³⁵U) UF₆. The study states that there are many issues yet to be resolved in establishing the maximum enrichment material that could be introduced into a 30B cylinder consistent with the current regulatory considerations (summarized above). Possible future work proposed by ORNL include:

• “Determination of realistic hydrogenated uranium residue (HUR) configurations to justify less conservative modeling approaches (realistic placement of HUR deposits);
• Research on justifying crediting more of the overpack configuration (more realistic spacing scenarios for transportation);
• More benchmark experiments in applicable ranges (intermediate energy ranges, experiments with UF₆ specifically);
• Research into quantifying added safety margins based on data-induced uncertainty (taking credit for analyzed energy ranges);
• Consideration of overpack design changes to introduce reactivity-reducing features; and/or
• Research on justifying crediting a thicker cylinder wall.”

NEI co-sponsored this work at the request of its members.  Given the very large number of 30B cylinders that are currently in service, this analysis by ORNL was considered to be an important first step to determine if the existing 30B cylinders can be used to transport HALEU (5-10 w/o ²³⁵U) or “LEU+” as referred to in the ORNL report.  NEI members, particularly utilities and fabricators with plans to introduce fuel with higher enrichment assays, were instrumental in moving this project forward.  It is not yet clear what the next steps will be; however, the U.S. NRC played a role in reviewing the ORNL conclusions.  This should give some level of confidence that the NRC will be ready to receive an application, when submitted, to amend the UX-30 package to support transport of UF₆ at higher enrichment levels.

UX-30 Certificate of Compliance 71-9196

Note that the report is not yet posted to the ORNL or NRC web sites.  A copy has been provided to WNTI for posting along with this monthly report.  The version obtained is available for public distribution.  When the report is available to download, the link will be provided in a future issue of Member News.