Diffusion of fission products and radiation damage in SiC

A major problem with most of the present nuclear reactors is their safety in terms of release of radioactivity into the environment during accidents. In some of the nuclear reactor designs, i.e. Generation IV reactors, the fuel is in the form of spherical particles, i.e. TRISO (acronym for Triple Coated Isotropic) particles. main function of these coating layers is to act as diffusion barriers for radioactive products, thereby keeping these fission products within the fuel particles, even accident conditions. The most important coating layer is composed of 3C-SiC. This paper reviews the diffusion of the important fission (silver, caesium, iodine and strontium) in SiC. Because radiation damage induce and enhance diffusion, the paper also briefly reviews damage created by neutrons and ions at elevated temperatures, i.e. the temperatures at which modern reactors will operate, and the annealing of the damage. The interaction SiC and some fission products (such as Pd and I) is also briefly discussed. shown, one of the key advantages of SiC is its radiation hardness at elevated , i.e. SiC is not amorphized by neutron or bombardment at substrate above 350°C. Based on the diffusion coefficients of the fission products , the review shows that at the normal operating temperatures of these new (i.e. less than 950°C) the SiC coating layer is a good diffusion barrier for fission products. However, at higher temperatures the design of the coated needs to be adapted, possibly by adding a thin layer of ZrC.