The ALMR contains 66 driver fuel assemblies arranged in concentric circles radially to form a cylindrical core. Each assembly is hexagonal in shape and contains 217 pins. Each pin is surrounded by a spiral spacer (pin separator) and is held in place by tube spacers. Each assembly is then encased in a flow tube.
Each fuel pin is 7.2 mm in diameter and is clad in a ferritic alloy called HT-9. For the reference core, the fuel pellets are made of a ternary metallic alloy of 25% enriched Uranium, 10% Plutonium, and Zirconium. Metallic fuel pellets are far better heat conductors than ceramics but, they have a lower melting temperature and lack internal voids necessary to contain fission gases. The ALMR, however, can also use ceramic and actinide enriched fuel pellets. This versatility ensures that a utility can make the most economical fuel choice.
