A nuclear reactor system includes a nuclear reactor core disposed in a pressure vessel. Nuclear reactor system further includes control drums disposed longitudinally within the pressure vessel and laterally surrounding fuel elements and at least one moderator element of the nuclear reactor core to control reactivity. Each of the control drums includes a reflector material and an absorber material. Nuclear reactor system further includes a control drum controller with a counterweight to impart a reverse torque on the control drum. Control drum controller includes a driven pulley coupled to the counterweight, a tension member coupled to the driven pulley to rotatably control the driven pulley and apply torque to the driven pulley, and an actuator to apply a tension force to the tension member. The actuator counteracts the reverse torque with the applied tension force, and the tension member applies the torque in response to the tension force.

A nuclear reactor system includes a nuclear reactor core disposed in a pressure vessel. Nuclear reactor system further includes control drums disposed longitudinally within the pressure vessel and laterally surrounding fuel elements and at least one moderator element of the nuclear reactor core to control reactivity. Each of the control drums includes a reflector material and an absorber material. Nuclear reactor system further includes a control drum controller with a counterweight to impart a reverse torque on the control drum. Control drum controller includes a driven pulley coupled to the counterweight, a tension member coupled to the driven pulley to rotatably control the driven pulley and apply torque to the driven pulley, and an actuator to apply a tension force to the tension member. The actuator counteracts the reverse torque with the applied tension force, and the tension member applies the torque in response to the tension force.

A variable diameter fuel rod of a nuclear reactor assembly is disclosed. The variable diameter fuel rod includes an elongated cladding tube configured to house a plurality of fuel pellets including a fissile material arranged in a fuel stack orientation. The elongated cladding tube includes first and second axial reflector regions and a middle axial region therebetween. The middle axial region comprises an outer diameter defined as d.sub.1. The first and second axial reflector regions include an outer cladding diameter defined as d.sub.2 and d.sub.3, respectively. The variable diameter fuel rod further includes a transitional region between the diameter d.sub.1 of the middle axial region and the diameter d.sub.2 of the axial reflector region. The diameter d.sub.2 of the axial reflector region is greater than the diameter d.sub.1 of the middle axial region.

A variable diameter fuel rod of a nuclear reactor assembly is disclosed. The variable diameter fuel rod includes an elongated cladding tube configured to house a plurality of fuel pellets including a fissile material arranged in a fuel stack orientation. The elongated cladding tube includes first and second axial reflector regions and a middle axial region therebetween. The middle axial region comprises an outer diameter defined as d.sub.1. The first and second axial reflector regions include an outer cladding diameter defined as d.sub.2 and d.sub.3, respectively. The variable diameter fuel rod further includes a transitional region between the diameter d.sub.1 of the middle axial region and the diameter d.sub.2 of the axial reflector region. The diameter d.sub.2 of the axial reflector region is greater than the diameter d.sub.1 of the middle axial region.

Radiation shielding and methods of manufacture are disclosed. A radiation shielding apparatus includes a matrix including matrix material; and a mixture positioned in the matrix, the mixture including: a neutron thermalizing material; and a neutron absorbing material mixed with the neutron thermalizing material. A reactivity control system includes a container rotatable around an axis; a divider positioned inside the container to define two or more compartments within the container; at least one neutron absorber positioned in at least one of the two or more compartments; and at least one neutron reflector positioned in another of the two or more compartments that is fluidly isolated from the at least one of the two or more compartments. A method of manufacturing radiation shielding material includes: fabricating a matrix; generating a mixture by mixing a neutron absorbing material, a neutron thermalizing material, and additive materials; and loading the mixture into the matrix.

Radiation shielding and methods of manufacture are disclosed. A radiation shielding apparatus includes a matrix including matrix material; and a mixture positioned in the matrix, the mixture including: a neutron thermalizing material; and a neutron absorbing material mixed with the neutron thermalizing material. A reactivity control system includes a container rotatable around an axis; a divider positioned inside the container to define two or more compartments within the container; at least one neutron absorber positioned in at least one of the two or more compartments; and at least one neutron reflector positioned in another of the two or more compartments that is fluidly isolated from the at least one of the two or more compartments. A method of manufacturing radiation shielding material includes: fabricating a matrix; generating a mixture by mixing a neutron absorbing material, a neutron thermalizing material, and additive materials; and loading the mixture into the matrix.

A flow control device configured to be positioned in a reactor core. The flow control device including a central shaft and at least one blade extending helically from the central shaft. A nuclear reactor and related systems and methods are also disclosed.

A nuclear reactor core mechanical support bracket is disclosed. The support bracket includes a housing, a spring disposed internally within the housing, a shaft slidingly disposed within the housing, a shaft travel pin, and a flange. The shaft is configured to engage the spring to compress and decompress the spring as the shaft travels in and out of the housing. The shaft travel pin controls the travel of the shaft. The flange is configured to mount the nuclear reactor core mechanical support bracket to a canister of a nuclear reactor. The shaft includes an inset configured to interface with a nuclear reactor core component.

A control rod drive system includes a drive assembly and a cage assembly operably coupled to the drive assembly. The cage assembly includes a plurality of drive rods operably engaged with a drive platform, a plurality of guide rods extending through the drive platform, and a control platform releasably coupled to the drive platform via quick release assembly, the control platform configured to have a control rod mounted thereto. A method of control operation of a nuclear reactor includes receiving instructions to adjust operation of the nuclear reactor, moving a control rod relative to a core of the nuclear reactor via rotating one or more drive rods engaged with a drive platform, and releasing a control platform coupled to the control rod from the drive platform.

A control rod drive system includes a drive assembly and a cage assembly operably coupled to the drive assembly. The cage assembly includes a plurality of drive rods operably engaged with a drive platform, a plurality of guide rods extending through the drive platform, and a control platform releasably coupled to the drive platform via quick release assembly, the control platform configured to have a control rod mounted thereto. A method of control operation of a nuclear reactor includes receiving instructions to adjust operation of the nuclear reactor, moving a control rod relative to a core of the nuclear reactor via rotating one or more drive rods engaged with a drive platform, and releasing a control platform coupled to the control rod from the drive platform.