A reference manual for low-activation materials development and the SiC case study

Low activity criteria for fusion reactor materials are defined and justified. The radioactive behaviour of Silicon Carbide is studied, when used as structural material for fusion applications, both in first wall and in blanket irradiation conditions. This analysis takes into account short- and long-term issues like accident safety, maintenance and waste management. The possible recycling of the material is also considered. According to these criteria, Silicon Carbide must be regarded as one of the most promising low-activation materials, as far as radiological/activation behaviour is concerned. The differences according to the possible use as first-wall and I or blanket structural material are pointed out. In all the instants after shut-down that are of interest for the criteria, a thorough study of the radioactive species produced by SiC is performed. The relative contributions of the alloying constituents and of the impurities are determined. SiC/SiC complies with all the proposed criteria. The long-term dose rate, however, is above the hands-on limit. Irradiation-decay chains leading to the formation of long-lived gamma-active radioisotopes (e.g., Al-26) are examined. Possible solutions to reduce the long-term dose rate are discussed, among which isotopic tailoring of Si and fine analysis of troublesome impurities.