A nuclear power system includes a reactor vessel that includes a reactor core that includes nuclear fuel assemblies configured to generate a nuclear fission reaction. A representative nuclear power system further includes a riser positioned above there actor core and a primary coolant flow path that extends from a bottom portion of the reactor vessel, through the reactor core, and through an annulus between the riser and the reactor vessel. A primary coolant circulates through the primary coolant flow path to receive heat from the nuclear fission reaction and release the heat to a power generation system configured to generate electric power. The nuclear power system further includes a control rod assembly system positioned in the reactor vessel and configured to position control rods in only two discrete positions.

Cover gas control systems include a reservoir and injection path for direct injection into fuel transfer machinery. If seals in the fuel handling machinery leak, cover gas is provided from the reservoir to flow to the leak without contamination from a reactor to which the fuel transfer machinery is joined. This providing cover gas may be passive or automatic in response to a detected low pressure level, detected ambient air ingress, low volume level of cover gas, or manually actuated through an operator. The cover gas may be injected from below the leak but above the reactor. A limitation in the injection path keeps cover gas injection at rates sufficient to allow operator reaction and sealing before the reservoir is depleted. A pressure pulse transmitter, blowout preventer, and transfer port plug are useable in the systems, which can be implemented in fuel handling machinery for reactors using a cover gas.

The modular lower moving system for nuclear fuel handling includes: a lower reactor vessel assembly including nuclear fuel loaded therein; a carrier having a space allowing the lower reactor vessel assembly to be accommodated therein; a rail extending from a reactor area to a fuel handling area; a transfer cart horizontally movable along the rail; a lifting device installed at the transfer cart, movable upward or downward with respect to the transfer cart; and a drive device configured to supply power to the transfer cart and the lifting device. The method of refueling nuclear fuel using the modular lower moving system includes a carrier lifting process, a lower reactor vessel assembly detachment process, a process of accommodating the lower reactor vessel assembly in the carrier, a carrier lowering process, a transfer cart movement process, a nuclear fuel offloading process, and a nuclear fuel loading process.

Nuclear reactors have very few systems for significantly reduced failure possibilities. Nuclear reactors may be boiling water reactors with natural circulation-enabling heights and smaller, flexible energy outputs in the 0-350 megawatt-electric range. Reactors are fully surrounded by an impermeable, high-pressure containment. No coolant pools, heat sinks, active pumps, or other emergency fluid sources may be present inside containment; emergency cooling, like isolation condenser systems, are outside containment. Isolation valves integral with the reactor pressure vessel provide working and emergency fluid through containment to the reactor. Isolation valves are one-piece, welded, or otherwise integral with reactors and fluid conduits having ASME-compliance to eliminate risk of shear failure. Containment may be completely underground and seismically insulated to minimize footprint and above-ground target area.

A nuclear power system includes a reactor vessel that includes a reactor core mounted therein. The reactor core includes nuclear fuel assemblies configured to generate a nuclear fission reaction. The nuclear power system further includes a chemical injection system configured to inject a chemical into the reactor vessel and remove the chemical from the reactor vessel, and a control system communicably coupled to the chemical injection system and configured to control a power output of the nuclear fission reaction. For example, the control system can determine that the power output is greater than an upper value of a range or less than a lower value of the range and, based on the determination, adjust an amount of the chemical injected into or removed from the reactor vessel by the chemical injection system to adjust the power output.

Nuclear reactors have very few systems for significantly reduced failure possibilities. Nuclear reactors may be boiling water reactors with natural circulation-enabling heights and smaller, flexible energy outputs in the 0-350 megawatt-electric range. Reactors are fully surrounded by an impermeable, high-pressure containment. No coolant pools, heat sinks, active pumps, or other emergency fluid sources may be present inside containment; emergency cooling, like isolation condenser systems, are outside containment. Isolation valves integral with the reactor pressure vessel provide working and emergency fluid through containment to the reactor. Isolation valves are one-piece, welded, or otherwise integral with reactors and fluid conduits having ASME-compliance to eliminate risk of shear failure. Containment may be completely underground and seismically insulated to minimize footprint and above-ground target area.

A nuclear power system includes a reactor vessel that includes a reactor core that includes nuclear fuel assemblies configured to generate a nuclear fission reaction; a riser positioned above the reactor core; a primary coolant flow path that extends from a bottom portion of the volume through the reactor core and through an annulus between the riser and the reactor vessel; a primary coolant that circulates through the primary coolant flow path to receive heat from the nuclear fission reaction and release the heat to generate electric power in a power generation system; and a control rod assembly system positioned in the reactor vessel and configured to position control rods in only two discrete positions.

A reactor vessel that includes a reactor core mounted within a volume of the reactor vessel, the reactor core comprising one or more nuclear fuel assemblies configured to generate a nuclear fission reaction, a riser positioned above the reactor core, the riser forming a primary coolant flow path, a steam generator thermally coupled to the riser, the steam generator communicatively coupled to a steam turbine through a steam inlet that includes a steam inlet valve, a secondary coolant flow path that extends through the steam generator, the secondary coolant flow path coupled to a coolant pump, and a control system coupled to both the steam inlet valve and the coolant pump, the control system configured to control a power output of the nuclear fission reaction by adjusting one or more parameters of the steam inlet valve or the coolant pump.

A sodium leak detection system for a nuclear reactor vessel includes a recirculation loop having an inlet and an outlet in communication with the annular space between the nuclear reactor vessel and the guard vessel. The recirculation loop and the annulus are filled with an inert gas, such as argon. The inert gas is doped with a known trace quantity of oxygen, typically in the single-digit ppm range up to about 1%. A recirculator forces the inert gas and oxygen to mix and flow throughout the annulus. The recirculation loop further includes a trace oxygen sensor that determines the concentration of oxygen in the inert gas. Because sodium reacts with oxygen, the trace oxygen sensor is monitored for a reduction in the oxygen level, which indicates a sodium leak into the annulus.

A core of a fast nuclear reactor has at least one gas expansion module, at least one neutron absorber, and at least one neutron moderator. The gas expansion module has a hollow tubular structure with one end closed and the other end opened. The at least one neutron absorber adjoins an outer face, in a radial direction of the core, of each gas expansion module. The at least one neutron moderator adjoins an outer face, in a radial direction of the core, of each gas expansion module. The at least one neutron absorber also adjoins the at least one neutron moderator.