A nuclear power system includes a reactor vessel that includes a reactor core mounted, the reactor core including 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 below the reactor core, through the reactor core, within the riser, and through an annulus between the riser and the reactor vessel back to the bottom portion of the volume; a primary coolant that circulates through the primary coolant flow path to receive heat from the nuclear fission reaction and release the received heat to generate electric power in a power generation system fluidly or thermally coupled to the primary coolant flow path; and a control system communicably coupled to the power generation system and configured to control a power output of the nuclear fission reaction independent of any control rod assemblies during the normal operation.

A nuclear power system includes a reactor vessel that includes a reactor core mounted, the reactor core including 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 below the reactor core, through the reactor core, within the riser, and through an annulus between the riser and the reactor vessel back to the bottom portion of the volume; a primary coolant that circulates through the primary coolant flow path to receive heat from the nuclear fission reaction and release the received heat to generate electric power in a power generation system fluidly or thermally coupled to the primary coolant flow path; and a control system communicably coupled to the power generation system and configured to control a power output of the nuclear fission reaction independent of any control rod assemblies during the normal operation.

A nuclear power generation system being safe and easily controlled by load following. The nuclear power generation system has a nuclear reactor employing a load following control method. The reactor includes: a fuel assembly reactor core having metallic fuel containing at least one selected from uranium-235, uranium-238 and plutonium-239; a reactor vessel containing the reactor core; metallic sodium loaded into the reactor vessel and heated by the reactor core; and a neutron reflector for achieving criticality in the reactor core with effective multiplication factor of neutrons emitted from the reactor core being maintained at or above about 1. The neutron reflector is coupled to spring or spiral metallic members and utilizing heat deformation in the metallic members due to the temperature in coolant metallic sodium to control the fast neutron reflection efficiency of the neutron reflector.

A nuclear power generation system being safe and easily controlled by load following. The nuclear power generation system has a nuclear reactor employing a load following control method. The reactor includes: a fuel assembly reactor core having metallic fuel containing at least one selected from uranium-235, uranium-238 and plutonium-239; a reactor vessel containing the reactor core; metallic sodium loaded into the reactor vessel and heated by the reactor core; and a neutron reflector for achieving criticality in the reactor core with effective multiplication factor of neutrons emitted from the reactor core being maintained at or above about 1. The neutron reflector is coupled to spring or spiral metallic members and utilizing heat deformation in the metallic members due to the temperature in coolant metallic sodium to control the fast neutron reflection efficiency of the neutron reflector.

Engineering safety systems always have insufficiencies in terms of safety, and construction of a complete safety system causes installation costs for the safety system to become very high. Provided is a small nuclear reactor HAVING a load following control system in which a nuclear reaction in the nuclear reactor is naturally controlled by the generated heat, the small nuclear reactor being provided with: a reactor core provided with a plurality of fuel assemblies of metallic fuels containing uranium (U) 235, 238 and/or plutonium (Pu) 239; a primary coolant comprising a liquid metal; a neutron reflector which serves to control the nuclear reaction in the reactor core and is disposed to enclose the periphery of the reactor core; and a mechanism which contains a liquid or a gas having an expansion coefficient greater than that of the neutron reflector, converts the coefficient of volumetric expansion into an amount of linear thermal expansion, and, by using same, moves the neutron reflector or adjusts the spacing between the plurality of fuel assemblies.

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.

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.

A control rod operation generates a rod insertion block signal during operation of a reactor. Four neutron detector assemblies including a plurality of LPRMs arranged in an axial direction of a core are arranged adjacent to a plurality of insertion selection control rods, respectively, which are simultaneously inserted into the core. Neutron flux ratio calculation units are arranged in each of the neutron detector assemblies, and ratios (neutron flux ratios B.sub.A/A.sub.A, C.sub.A/A.sub.A, and D.sub.A/A.sub.A) of an average LPRM signal of the respective LPRMs at positions B, C, and D to an average LPRM signal of the respective LPRMs at a position A which is closest to the control rod insertion end of the core are calculated. When the largest neutron flux ratio out of the neutron flux ratios exceeds a set neutron flux ratio, a rod insertion block signal which is generated by a local range rod insertion monitor is output.

A method for controlling a nuclear reactor includes acquiring current values of operating parameters of the reactor; and iteratively implementing the sub-steps of generating a sequence of injection of neutron poison and/or water; calculating an evolution in at least one magnitude characteristic of the state of the core of the nuclear reactor during this given time interval using a power program, current values of operating parameters and the injection sequence considered, the evolution being calculated using a predictive model of the core of the reactor; evaluating a cost function, using the calculated evolution; repeating the generating and calculating sub-steps until a convergence criterion of the cost function is met; and repeating the acquiring and the iteratively implementing steps with a time period less than 60 minutes.

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.