Formation and Annihilation of 26AL in sic Composites in Fusion Neutron Environment

The induced activity of SiC/SiC composites as a first wall material is evaluated by simulation calculations for the reactor structural model based on the alloy or impurity concentrations in the various composites prepared with chemical vapor infiltration (CVI) process. Nuclear data for the calculations are FENDL/A-2.0, JENDL3.2 and ENDF/B-VI. It was assumed that the composites of the first wall of the blanket were irradiated for 10 MW.a/m². The dose rate of SiC composites at the first wall after irradiation sharply decreases by 5 orders magnitude in a day. However, the dose rate of ²⁶Al produced from ²⁸Si is kept at about 100μSv/h for longer time than 100 k years. Al content at 2 mass % in Tyranno-SA SiC fiber increases the dose rate by about two orders of magnitude of pure SiC. Moreover, the annihilation of ²⁶Al has been examined with a simulation calculation where Al is assumed to be irradiated in thermal nuclear reactors after exposure of fusion neutrons. The amount of ²⁶Al is reduced to be 1/2 of the initial value after 50 years irradiation in HFIR reactor.