Effect of helium on radiation swelling of SiC

Ceramic materials produced on the basis of SiC and SiC/SiC composites are considered, due to their high-temperature strength, pseudo-ductile fracture behavior and low-induced radioactivity, as candidate materials for fusion reactors. The radiation resistance of ceramic materials under neutron irradiation is one of the key problems, which determines the use of these materials in fusion reactor environment. The dimensional stability (radiation swelling) of SiC is an important problem for degradation of radiation resistance of SiC materials. In fusion reactor environment helium atoms will be produced in SiC in the first wall region up to very high concentrations (15,000-20,000 at.ppm) and therefore it is very important to understand the helium effect on radiation swelling of SiC. In the present paper the effect of helium on radiation swelling of SiC is investigated. Recent experimental results concerning the helium effect on radiation swelling of SiC under neutron, single-ion and dual-beam irradiation are presented. A new theoretical model is suggested for an explanation of the effect of helium on radiation swelling in ceramic materials. Point defects in ceramic materials can have an effective charge (e.g., an F⁺_centre, vacancy with a single trapped electron). The suggested theoretical model is based on kinetic consideration of charged point defect accumulation and kinetic growth of dislocation loops in a matrix of ceramic material (SiC) taking into account the effect of internal electric fields formed under irradiation near dislocation loops on diffusion processes of charged point defects. In this theoretical model, vacancies and small vacancy clusters are considered as additional traps for helium atoms. This results in enhanced growth rate of dislocation loops and finally swelling increase. The obtained numerical and analytical theoretical results for radiation swelling in the presence of helium atoms are compared with the existing experimental data for irradiated SiC material containing helium atoms. It has been shown that helium atoms increase the radiation swelling of SiC.