Abstract: A method is provided for operating a nuclear reactor. The method includes operating the nuclear reactor for at least one plutonium equilibrium cycle during which the core contains plutonium-equilibrium nuclear fuel assemblies; subsequently, operating the reactor for transition cycles, at least some of the plutonium-equilibrium nuclear fuel assemblies being progressively replaced with transition nuclear fuel assemblies and then with uranium-equilibrium nuclear fuel assemblies; and then operating the nuclear reactor for at least one uranium equilibrium cycle.

Abstract: The present invention relates to nuclear fuel compositions including triuranium disilicide. The triuranium disilicide includes a uranium component which includes uranium-235. The uranium-235 is present in an amount such that it constitutes from about 0.7% to about 5% by weight based on the total weight of the uranium component of the triuranium disilicide. The nuclear fuel compositions of the present invention are particularly useful in light water reactors.

Abstract: A reactor core cooling structure of the present invention comprises cooling gas flow-in slits for making a cooling gas flow in a circular reactor core, which slits are provided at an outer graphite cylinder for covering an outside of the circular reactor core; cooling gas flow-out slits for making the cooling gas flow in a circular reactor core, which slits are provided at an inner graphite cylinder for covering an inside of the circular reactor core; a circular cooling gas flow path that is provided at an outside of the outer graphite cylinder, and is connected to an inlet piping of the cooling gas at a foot of the outer graphite cylinder; and an inner cooling gas flow path that is provided at an inside of the inner graphite cylinder, and is connected to an outlet piping of the cooling gas at a foot of the inner graphite cylinder.

Abstract: An accurate method for testing the strength of nuclear fuel particles. Each particle includes an upper and lower portion, and is placed within a testing apparatus having upper and lower compression members. The upper compression member includes a depression therein which is circular and sized to receive only part of the upper portion of the particle. The lower compression member also includes a similar depression. The compression members are parallel to each other with the depressions therein being axially aligned. The fuel particle is then placed between the compression members and engaged within the depressions. The particle is then compressed between the compression members until it fractures. The amount of force needed to fracture the particle is thereafter recorded. This technique allows a broader distribution of forces and provides more accurate results compared with systems which distribute forces at singular points on the particle.

Abstract: A nuclear propulsion reactor. A reactor vessel is provided with an annular first core and a cylindrical second core that is radially encompassed by the first core. Nuclear fuel elements in the first core provide first stage heating of propellant as they direct the propellant axially through the first core. The second core, which contains fissionable material in a highly refractory form, is in fluid communication with the first core for receiving the heated propellant. Fission reactions in the second core driven by leakage neutrons from the first core provide second stage heating of the propellant as it passes therethrough. The second core directs the coolant to a propellant nozzle for providing propulsive thrust.

Abstract: A gas cooled nuclear fuel element having a particle fuel retention device which acts as a passive restraint in the event of failure of hot frit. A particle fuel retention device is positioned either in the annular space within the inner frit, in the end cap through which coolant gas flows, or attached to the end cap and extending axially beyond the fuel element.

Abstract: A nuclear fuel element for a particle bed reactor. Concentric inner and outer porous cylinders attached at either end define an annulus therebetween that contains a fuel particle bed of nuclear fuel material. The outer porous cylinder is provided with fins that extend radially outward along its entire length. A nonporous cylinder is attached to the outer porous cylinder at either end and is positioned around the outer porous cylinder so as to be concentric therewith. Flexible fins extend radially inward form the nonporous cylinder along its entire length and contact the fins on the outer porous cylinder for conduction of heat to heat removal tubes on the outer surface of the nonporous cylinder. The heat removal tubes allow bimodal cooling of the particle bed reactor.

Abstract: A particle bed fuel element designed to accommodate expansion and contraction within the particle fuel bed. Porous inner and outer frits connected together by an end cap at a first end and radially guided by a shoulder at a second end receive fuel particles in the annulus formed therebetween. Compressive devices at each end of the frits and within the fuel bed maintain packing force to prevent looseness during contraction and allow expansion without excessive pressure being placed on the fuel particles. Pairs of beleville springs, wave springs, and pressurized thin-walled metal donuts may be used as the compressive devices.