A transportable nuclear power generator, comprising: • a plurality of subcritical power modules, each comprising: ∘ a fuel cartridge containing a nuclear fuel and having a proximal end and a distal end; ∘ a power conversion unit comprising: ▪ a compressor turbine disposed at the proximal end of the fuel cartridge and driven by a compressor motor; and ▪ a power turbine disposed at the distal end of the fuel cartridge to convert thermal energy into electricity via a generator; ∘ a pressure boundary substantially enclosing the fuel cartridge, the compressor turbine, the power turbine; and ∘ heat exchangers (204, 208, 214), • actuators adapted to move each of the subcritical power modules, wherein at least one of the plurality of subcritical power modules is movable with respect to the other of the plurality of subcritical power modules between a first position and a second position to control criticality of the nuclear fuel contained in the fuel cartridges of the plurality of subcritical power modules,wherein the nuclear fuel in the fuel cartridges of the plurality of subcritical power modules is configured to remain in a sub-critical state when the at least one of the plurality of subcritical power modules is in the first position, and wherein the nuclear fuel in the fuel cartridges of the plurality of subcritical power modules is configured to reach a critical state when the at least one of the plurality of subcritical power modules is in the second position. • a plurality of subcritical power modules, each comprising: ∘ a fuel cartridge containing a nuclear fuel and having a proximal end and a distal end; ∘ a power conversion unit comprising: ▪ a compressor turbine disposed at the proximal end of the fuel cartridge and driven by a compressor motor; and ▪ a power turbine disposed at the distal end of the fuel cartridge to convert thermal energy into electricity via a generator; ∘ a pressure boundary substantially enclosing the fuel cartridge, the compressor turbine, the power turbine; and ∘ heat exchangers (204, 208, 214), ∘ a fuel cartridge containing a nuclear fuel and having a proximal end and a distal end; ∘ a power conversion unit comprising: ▪ a compressor turbine disposed at the proximal end of the fuel cartridge and driven by a compressor motor; and ▪ a power turbine disposed at the distal end of the fuel cartridge to convert thermal energy into electricity via a generator; ▪ a compressor turbine disposed at the proximal end of the fuel cartridge and driven by a compressor motor; and ▪ a power turbine disposed at the distal end of the fuel cartridge to convert thermal energy into electricity via a generator; ∘ a pressure boundary substantially enclosing the fuel cartridge, the compressor turbine, the power turbine; and ∘ heat exchangers (204, 208, 214), • actuators adapted to move each of the subcritical power modules, wherein at least one of the plurality of subcritical power modules is movable with respect to the other of the plurality of subcritical power modules between a first position and a second position to control criticality of the nuclear fuel contained in the fuel cartridges of the plurality of subcritical power modules,wherein the nuclear fuel in the fuel cartridges of the plurality of subcritical power modules is configured to remain in a sub-critical state when the at least one of the plurality of subcritical power modules is in the first position, and