Helium gas permeability of SiC/SiC composite used for in-vessel components of nuclear fusion reactor

SiC/SiC composite is a candidate material of blanket in fusion reactors since silicon carbide is a low activation material and the temperature of helium coolant can be taken high, 1100 K. Helium gas permeability of SiC/SiC composite, however, has been little measured so far for this purpose. For SiC/SiC composites made by several methods, the helium gas permeability was measured using a vacuum system consisting of high and low-pressure chambers, and its application for the blanket was discussed. The permeability of SiC/SiC composite made by the method called as nano-powder infiltration and transient eutectoid (NITE) process was observed to be very low, 10-11 m2/s. A change of the permeability owing to heat cycles was also measured. The increase of the permeability was observed to be not large. The leak flux of helium through the SiC/SiC coolant pipe and first wall of blanket module was analyzed based upon the density balance of helium. It is shown that the leak rate into fusion plasma can be taken lower the helium production rate due to fusion reactions if the pumping is attached to the blanket module. Then, the fuel dilution due to the helium leak may be avoided even when the SiC/SiC blanket modules are employed