Effect of Fission Products and Oxygen and Carbon Impurities in (U, Pu)N on the Heat-and-Mass Transfer Coefficients and Xenon Yield

Abstract

Irradiation of uranium-plutonium mononitride by fast neutrons results in the formation and accumulation of fission products, which, for example, lanthanides, zirconium, and yttrium, dissolve in the fuel solid solution, changing its chemical composition and stoichiometry, or precipitate in the form of individual condensed phases, changing the phase composition of the fuel. These phase inclusions are formed inside and on the boundaries of fuel grains, changing the coefficients of heat-and-mass transfer. A change in the effective coefficient of heat-and-mass transfer results in a transformation of the temperature field in a fuel element, which means that the temperature part of the diffusion coefficient changes. The diffusion coefficient in solid phase inclusions is different from the diffusion coefficient in the fuel matrix, as a result of which the effective diffusion coefficient changes. A model of the yield of stable, radioactive, inert gases from uraniumplutonium mononitride fuel is presented and used to calculate the xenon yield taking account of the changes in the coefficients of heat-and-mass transfer and diffusion.