PARTICULARS OF URANIUM DIOXIDE MASS TRANSFER IN HIGH-TEMPERATURE UNVENTED FUEL ELEMENT

摘要

High-temperature fuel elements in nuclear power plants with dynamic energy conversion are unvented (hermetic) and filled with helium at pressure reaching several atmospheres at working temperature [1,2]. Mass transfer of uranium dioxide in such fuel elements occurs by diffusion with a relatively low initial rate, which subsequently decreases additionally because the pressure of the gaseous fission products flowing out of the fuel increases and the cross section of the collisions with uranium dioxide particles is larger. Mass transfer in the central channel and interior of the kernel of a fuel element has not been studied in detail, which makes it impossible to choose an optimal design for such a fuel element for the prescribed working parameters. In the present communication, we describe a method for calculating the mass transfer of uranium dioxide in an unvented fuel element that, together with a previous method developed for vented fuel elements [3], makes it possible to perform a comparative analysis of mass transfer. Transfer of Uranium-Containing Components in the Central Channel of a Kernel. The basic equations describing the mass transfer of fuel in a channel in the vacuum regime were obtained in . In the derivation, it was assumed the evaporation of molecules from the wall is an equilibrium process and the coefficients of evaporation and condensation were assumed to equal 1.