Berechnung des Spaltprodukttransportes in SiC beschichteten Brennelementen für Hochtemperaturreaktoren

摘要

A new development in graphite fuel elements for high temperature reactors is the application of a silicon carbide coating. This coating protects the fuel elements from corrosion during hypothetical water and air exposure in the reactor core. The fission product transport in these improved fuel elements shows a different behaviour than that in conventional graphite fuel elements. An analysis of the fission product behaviour is the subject of this work. The fission product release mechanism depends mainly an the porosity in the silicon carbide coating. Inside the graphite matrix of the fuel element the transport can be described with a two- or threedimensional diffusion model. The necessary diffusion parameters are well known and validated by many experiments. The major part of this work deals with the development of a threedimensional diffusion code for cartesian, cylindrical and sperical geometry. Since there exist no experimental data for the chemical interaction of fission products and graphite, the build in feature of activity coefficients can not yet be used. The results of the present diffusion calculations Show, that the fission product release behaviour is essentially proportional to the time and to the radius of the pores.