The SMRs of different coolant types employ very different fuel types. The water — cooled as well as the lead-bismuth-cooled SMRs use uranium dioxide (UO2) ceramic fuel; the gas-cooled SMRs use graphite and silicon carbide coated UO2 particles in graphite compacts or pebbles; the sodium-cooled reactor uses metallic UZr with minor actinides; and the lead-cooled SMR uses mononitride mixed fuel (UN-PuN). The water-cooled SMR fuel is the same as that of the operating plants and of the GEN Ш+ plants currently being deployed. All the liquid-metal-cooled reactor fuels will have an enrichment significantly more than the 5% of current water-cooled fuel.

Although a US national repository is not yet identified, this water-cooled SMR fuel will be handled consistent with the anticipated US policy yet to be finalized. The gas-cooled SMR fuel, the same as that used in the Fort St. Vrain reactor, has significantly more volume per unit energy generation but lower heat load per unit volume than LWR UO2 fuel. The characteristic of this fuel will require a different overall disposal strategy, although it would likely be compatible with the the strategy of the national repository for ceramic UO2-zircaloy clad fuel since the tristructural isotropic-type (TRISO) fuel particles form good barriers that provide excellent fission product retention.

The fuel of sodium — and lead-cooled SMR reactors exploits the inherent incentive of these fast neutron spectrum reactors to undergo reprocessing and recycling. This fuel cycle will entail construction and operation of reprocessing and fuel fabrication facilities while most likely it would also be integrated with reprocessing of some light water fleet fuels as feedstock for the plutonium needed for initial loading of a growing fleet of fast reactors. The spent fuel constituents ultimately requiring disposal will be predominantly fission products of much less volume than the spent fuel bundles of thermal spectrum water reactors per equivalent unit of energy generated. However, the deployment of fast spectrum SFRs based on the closed fuel cycle would require significant expansion of reprocessing and fuel fabrication facilities compared to the needs for the existing LWR fleet and LWR SMRs operating on the once-through fuel cycle.