NRC's July transport rule modernizes shielding limits but leaves HALEU criticality problem unsolved

A guest analysis published 12 August 2026 by Elliot Marsh of NeutronRise on Neutron Bytes makes a point that the nuclear trade press has largely missed: the NRC's 27 July proposed rule modernizing transportation package certification is useful for moving irradiated microreactors, but it does not address the constraint that actually governs moving HALEU fuel to a reactor site before first startup.^[1]

What the proposed rule does - and does not - do

On 27 July 2026, the NRC published a proposed rule to modernize 10 CFR Part 71, its regulations governing the transportation of radioactive materials. The headline changes are real: the rule would allow applicants to use risk-informed or performance-based approaches to demonstrate package safety, and it would raise the permitted radiation level at two metres from a Type B package from 0.1 mSv/hour to 0.5 mSv/hour under exclusive-use conditions - a fivefold increase that could reduce shielding mass and cost for irradiated microreactor shipments.

Trade coverage framed this as a step toward easier microreactor deployment, and that framing is fair as far as it goes.^[1] But shielding is an engineering problem. The NRC's own proposed rule projects that if all microreactors built over a 40-year period had their shielding reduced by half an inch, the industry could save $52.5 million undiscounted - roughly $0.48 million a year. That is a marginal gain, not a structural unlock.

The structural problem is criticality safety for unirradiated HALEU, and the proposed rule does not touch it.

Why HALEU transport is the harder problem

HALEU is uranium enriched to between 5 and 20 weight percent U-235, compared with the 5 percent or less used in conventional light-water reactor fuel. The higher enrichment is what allows advanced reactor cores to be small, long-lived, and fuel-efficient. It is also what makes the fuel difficult to ship in commercial quantities.

The physics is unforgiving. Under NRC regulations, applicants must demonstrate that a HALEU-containing package will remain subcritical under all credible accident conditions - drop, fire, immersion. The challenge is that there are relatively few validated critical experiments in the HALEU enrichment range to benchmark the computer codes used to make that demonstration. Wider safety margins must therefore be applied, which in turn limits how much fissile material can fit in a certified package.

The economic consequence is stark. Existing NRC-certified casks designed for UF₆ enriched above 5 weight percent are limited to payloads of roughly 255 lbs for type 8A casks (rated to 12.5% enrichment) and as little as 54.9 lbs for type 5A/5B casks. At those payload limits, no approved package permits the economical transport of HALEU in the quantities a commercial fuel cycle requires.

As of mid-2026, the United States has no NRC-certified transportation package capable of moving HALEU at commercial scale.

Where the supply chain stands

The gap is known and being worked. Key parallel efforts underway:

• DOE transport awards: In July 2025, DOE awarded $11 million to five companies - NAC International, Westinghouse, Container Technologies Industries, American Centrifuge Operating, and Paragon D&E - to develop and seek NRC certification for new HALEU transport package designs, with performance periods of up to three years.
• NANO Nuclear / GNS: In March 2026, NANO Nuclear reported completing conceptual designs for two optimized HALEU fuel payload baskets and a preliminary overpack design, developed with German nuclear logistics specialist GNS, with engineering validation and NRC certification still ahead.
• Criticality benchmarking: DOE and NRC are running a joint programme at Oak Ridge National Laboratory to generate the critical experiment data needed to reduce licensing uncertainty for HALEU fuel cycle and transport applications.

On the fuel fabrication side, progress is faster. In February 2026, the NRC granted X-energy subsidiary TRISO-X a special nuclear material license for HALEU fuel fabrication at its Oak Ridge facility - the first new nuclear fuel fabrication plant licensed by the NRC in more than 50 years. TRISO fuel for Radiant's Kaleidos demonstration at Idaho National Laboratory's DOME facility was delivered earlier this year. Radiant has also received a second DOE HALEU allocation to fuel a Kaleidos unit at Buckley Space Force Base in Colorado, with delivery targeted for 2028.

The sequence matters. Moving a microreactor without fuel is a logistics exercise. Moving the fuel to the reactor site is the regulatory and engineering milestone that actually gates first startup for any commercial deployment.

What to watch

The DOE transport package awards run through 2027-2028 at the latest. Whether any of the five awardees can achieve NRC certification within that window - and at a payload size that makes commercial fuel logistics economical - is the critical path item for the first wave of HALEU-fuelled advanced reactors. The NRC's proposed Part 71 rule, with comments due 26 August 2026, is a useful modernisation of the shielding framework. It is not a solution to the criticality problem that sits underneath it.