Abstract: The invention relates to a nuclear fuel storage unit (10) which includes a vessel (12) and at least one tubular member (22) which extends through the vessel (12), opposite ends thereof opening out of the vessel (12) at spaced apart positions, to define an internal coolant flow path and such that a fuel receiving cavity (24) is defined between an outer surface of the at least one tubular member (22) and an inner surface of the vessel (12). The configuration of the fuel receiving cavity (24) is such that the packing density and geometry of fuel received in the fuel receiving cavity (24) is such that the fuel remains sub-critical. The storage unit (10) includes also at least one fuel loading passage (26) leading into the fuel receiving cavity (24) whereby fuel to be stored can be introduced into the fuel receiving cavity (24).