The behavior of the main components of uranium dioxide, gaseous impurities, and fission products and the transfer of emitter material to a collector under conditions where the fuel-element and interelectrode gaps of a multicomponent electricity generating channel (EGC) communicate with one another are examined. The results of in-reactor experimental investigations of the temperature zones of condensation of fission products, using uranium dioxide based model fuel, and circuit tests of EGC are presented. It is shown that fission product settling on the collector is negligible; tungsten transfer from the emitter onto the collector can counterbalance this effect.A multicomponent electricity generating channel (EGC) with communicating fuel element and interelectrode cavities gives the most acceptable mass/size characteristics of a converter reactor in a built-in space nuclear power system as a result of fewer structural materials in the core and a smaller spacing between serially connected electricity generating components. The relative simplicity of such a construction also makes it technologically more adaptable, and the presence of the working body of the interelectrode gap (cesium) in the fuel element cavity retards mass transfer and simultaneously limits the emission of uranium dioxide and simplifies the gas removal system through which fission products are removed from the fuel elements. The problematic task in such a structural arrangement of the EGC is limiting the flow of impurity elements as well as the main components and fission products of oxide fuel through the gas removal system into the interelectrode gap.The gas medium in the interelectrode gap is formed, just as in the case of separate cavities, by the residual technological gases and technological gases adsorbed on the electrode surfaces, by the products of activation of cesium and fission of fuel, which pass through the emitter shell, as well as hydrogen flowing from the zirconium hydride moderator. These processes change the adsorption, emission, and radiative properties of the electrodes, and taken together they can degrade the electric power output of the EGC.Technical solutions involving the reactor and thermionic converter have now been developed to ensure stable operation of EGC:• the flow of hydrogen into the interelectrode gap is limited to pressures 10 -3 -10 -4 Pa by introducing diffusion barriers along the path to the EGC and sinks in front of these barriers; at higher pressures, the oxide ceramic of the spacers is reduced and at lower pressures the role of hydrogen in the reduction of tungsten oxides deposited on the collector is decreased, which decreases the density and results in weak adhesion followed by separation of the oxide layer when the thickness reaches about 30 µm [1, 2];
After fast neutron irradiation, uranium-plutonium nitride U 0.8 Pu 0.2 N is shown to acquire a com plex structure consisting of a solid solution that is based on the nitrides of uranium, plutonium, americium, neptunium, zirconium, yttrium, and lanthanides and contains condensed phases U 2 N 3 , CeRu 2 , BaTe, Ba 3 N 2 , CsI, Sr 3 N 2 , LaSe, metallic molybdenum, technetium, and U(Ru, Rh, Pd) 3 intermetallics. The con tents and compositions of these phases are calculated at a temperature of 900 K and a burn up fraction up to 14% (U + Pu). The change in the composition of the irradiated uranium-plutonium nitride is studied during the electron decay of metallic radionuclides. The kinetics of transformation of U 103 Ru 3 , 137 CsI, 140 Ba 3 N 2 , and 241 PuN is calculated.
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