Abstract: 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.

Abstract: Engineered surfaces, such as surfaces having nano- and/or micro-scale features, may provide an enhanced flow boiling Critical Heat Flux (CHF) at ambient or higher pressures, which may enhance cooling. Enhancing flow boiling CHF may be desirable for nuclear reactors, where heat is generated by a heater such as a nuclear reactor core. Enhanced flow boiling CHF may provide larger safety margins and/or better economics of nuclear reactors, for example, because reactor power rating may be increased as cooling is enhanced.