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[en] The hot pressing characteristics of uranium nitride and mixed uranium plutonium nitride were studied. The utilization of computer programs together with the experimental technique developed in the present study may serve as a useful purpose of prediction and fabrication of advanced reactor fuel and other high temperature ceramic materials for the future. The densification of nitrides follow closely with a plastic flow theory expressed as: d rho/ dt = A/T(t) (1-rho) [1/1-(1-rho)/sup 2/3/ + B1n (1-rho)] The coefficients, A and B, were obtained from experiment and computer curve fitting. (8 figures) (U.S.)

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[en] Gibbs free energies of the mixed nitrides, (U, Pu)N_1-x, were modelled with a sublattice formalism. The nonstoichiometry of the nitrides was taken into account by considering the mixing of nitrogen atoms and vacancies on the nonmetal sublattice of the NaCl-type structure. Starting from the modelling of UN_1-x and PuN_1-x, the equilibria involving (U, Pu)N_1-x were predicted. With a small addition of PuN to UN, the uranium vapor pressure, p(U), should be significantly suppressed. At the same time, temperature dependence of p(U) should be appreciably larger than p(U) over the uranium nitride. The effects of stoichiometry and impurities were examined by comparing the model prediction with the experimental data in the literature. (orig.)

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[en] Properties of neptunium-plutonium mixed nitride solid solutions were investigated. The solid solutions covering the whole range of composition were prepared by heating the mixtures of NpN and PuN in nitrogen-hydrogen mixed gas stream at 2023 K. Formation of high-purity solid solution with a single phase was confirmed by X-ray diffraction and chemical analyses and composition dependence of the lattice parameters was examined. Vaporization behavior over the solid solutions was investigated by Knudsen-mass spectrometry and temperature dependence of the partial pressures of Np(g) and Pu(g) was examined. Furthermore, the thermal conductivities were determined from the thermal diffusivities measured and specific heat capacities estimated. The thermal conductivities of the solid solutions lay between those of NpN and PuN. (authors)

[en] The paper describes the author's experience in design, manufacturing and implementing equipment for Mixed Uranium - Plutonium Oxide and Nitride fuel pellet fabrication in Russia. The key features of mixed uranium-plutonium oxide and nitride powders are described, as well as their influence on main process (furnaces, presses) and auxiliary (gloveboxes) equipment design. Technical solutions for working with low fluidity powders, conveyance systems for boats prone to deformation, gas separation systems, furnace insulation material choice, as well as rules and regulations applicable for this kind of equipment are discussed. (author)

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[en] Short communication