CERAMIC MATERIALS FOR FUSION REACTORS.

The use of low-activity ceramics, primarily silicon carbide, will eliminate the generation of large quantities of highly radioactive waste materials during operation of the fusion reactor and may well be required if fusion wishes to maintain its image as the clean source of power of the future. A biological hazards analysis indicates that fusion reactor first walls and blankets constructed of conventional materials like stainless steel still have half the biological hazard potential of fission reactor cores. The use of silicon carbide will reduce the biological hazard potential by 4 to 9 orders of magnitude depending on the purity of the silicon carbide. Materials studies have identified siliconized silicon carbide as the most promising material. It has a long-term service limit of 1200 degree C and can be fabricated in large shapes. Its strength and Weibull modulus do not decrease significantly at 1200 degree C after fast neutron irradiation up to a fluence of 1. 2 multiplied by 10**2**5 n/m**2. However, its thermal conductivity is reduced markedly during irradiation. Laboratory tests show that this affects the thermal shock resistance of silicon carbide adversely. How this will change the design of silicon carbide first walls remains to be evaluated.