A method of producing a light water reactor fuel assembly may include: setting conditions at least concerning an operation cycle period and burnup; setting an initial enrichment of enriched uranium; calculating excess reactivity of a light water reactor core where light water reactor fuel assemblies including the enriched uranium are burned until an end stage of a final operation cycle; determining whether a condition where excess reactivity at an end of a first operation cycle in the burnup calculation step is close to a predetermined positive value is true or not; and returning to the setting of the initial enrichment, when it is determined at the determining that the situation is not true, or deciding an enrichment of the enriched uranium when it is determined that the situation is true.

The invention relates to nuclear physics, and specifically to reactor fuel elements and units thereof, and particularly to the composition of solid ceramic fuel elements based on uranium dioxide, intended for and exhibiting characteristics for being used in variously-purposed nuclear reactors. The result consists in a more reliable, special structure and a simple composition of uranium dioxide without heterogeneous fuel pellet additives, approaching the characteristics of a monocrystal having enhanced, and specifically exceeding reference data, thermal conductivity as temperature increases, and a simple production method thereof. The result is achieved in that pores of between 1 and 5 microns in size are distributed along the perimeters of grains in the micro-structure of each metal cluster in a nuclear fuel pellet, and in that located within the grains are pores which are predominantly nano-sized. In addition, the metal clusters comprise between 0.01 and 1.0 percent by mass. The invention provides for a method of preparing a nuclear fuel pellet, including precipitating metal hydroxides, in two stages, having different pH levels. Uranium metal is melted at a temperature exceeding 1150 DEG C., sintering is carried out in an insignificant amount of liquid phase at a temperature ranging between 1600 and 2200 DEG C. in a hydrogen medium until forming uranium dioxide, the structure of which includes metal clusters dispersed therein. An X-ray photon spectroscope is used for identifying the new structure of the UO2 pellet and the additional UU chemical bond.

A method of making a nuclear fuel pellet for a nuclear power reactor. The method includes: providing a nuclear fuel material in powder form, pressing the powder such that a green pellet is obtained; providing a liquid that comprises an additive which is to be added to the green pellet; contacting the green pellet with the liquid so the liquid, with the additive, penetrates into the pellet; and sintering the treated green pellet. The additive is such that larger grains in the nuclear fuel material are obtained with the additive.

A method of making a nuclear fuel pellet for a nuclear power reactor. The method includes: providing a nuclear fuel material in powder form, the nuclear material is based on UO.sub.2; providing an additive; forming a green pellet, wherein said additive is added either to said nuclear fuel material or to the green pellet; and sintering the green pellet, wherein said additive causes larger grains in the nuclear fuel pellet, and wherein said additive is made of or includes a substance which causes the larger grains and which substantially leaves at least an outer portion of the pellet before and/or during the sintering step, wherein said substance is made of, or comprises, B and/or Cr.

A multiphase composite, formed by freeze-casting, lyophilization, and sintering, has sintered particles forming a scaffold having at least one region of aligned porosity; and a second phase formed in pores of the scaffold. In a particular embodiment, the second phase is a nuclear fuel, in another, the first phase is a nuclear fuel, and in others, both phases are nuclear fuels. In some embodiments, the first phase is a ceramic, and in other embodiments a metal such as stainless steel. In other embodiments, the second phase is a metal, and in other embodiments a ceramic. In some embodiments the second phase is positioned in a subset of pores of the scaffold, at least some additional pores being filled with a third phase. In embodiments, the second phase is also sintered.

The invention relates to the ROANEX method, which extracts actinides from used nuclear fuel in a single purification cycle. The used nuclear fuel contains actinides, U, Am, Pu, Np. and Cm, and fission products, Cs, Sr and Tc. The fission products are separated first from the used nuclear fuel. The actinides are reduced to their lowest oxidation states and then oxidized to their highest oxidations states. Uranium, Pu and Np move to an organic phase solution and Am and Cm move to a nitrate solution. Uranium, Pu, and Np are stripped from the organic phase solution, and then treated with an oxalic acid to form a precipitate. Americium and Cm are treated with a potassium carbonate solution and Am precipitates. Actinides Am, U, Pu, and Np precipitates are heated in an oven and then blended together to form a mixed oxide fuel of UO.sub.2, PuO.sub.2, NpO.sub.2 and AmO.sub.2.

The application discloses a preparation method of monocrystal uranium dioxide nuclear fuel pellets, comprising: granulating and pelleting UO.sub.2 powder to obtain UO.sub.2 pellets; then coating surfaces of the UO.sub.2 pellets with monocrystal growth additive micro powder to form core-shell structure particles; and activated-sintering the core-shell structure particles at high temperature, liquefying the monocrystal growth additive on the surface of the core-shell structure particle at high temperature and then diffusing into UO.sub.2 pellets, dissolving the UO.sub.3 in the liquid monocrystal growth additive, and recrystallizing the UO.sub.2 to form the monocrystal UO.sub.2 nuclear fuel pellets.

A multiphase composite, formed by freeze-casting, lyophilization, and sintering, has sintered particles forming a scaffold having at least one region of aligned porosity; and a second phase formed in pores of the scaffold. In a particular embodiment, the second phase is a nuclear fuel, in another, the first phase is a nuclear fuel, and in others, both phases are nuclear fuels. In some embodiments, the first phase is a ceramic, and in other embodiments a metal such as stainless steel. In other embodiments, the second phase is a metal, and in other embodiments a ceramic. In some embodiments the second phase is positioned in a subset of pores of the scaffold, at least some additional pores being filled with a third phase. In embodiments, the second phase is also sintered.

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.

A method for preparing a UO.sub.2 mixture powder for nuclear fuel manufacturing, comprises the steps of: (a) weighing and sieving, by means of an automatic injection device, a UO.sub.2 powder, a porogen and a lubricant, and injecting same into a UC container; and (b) mixing the UO.sub.2 powder, the porogen and the lubricant by means of an IBC blender. According to a method for preparing a UO.sub.2 mixture powder for nuclear fuel manufacturing, mixing time is short, and degrees of mixing and homogeneity of a prepared UO.sub.2 mixture powder are excellent.