ASSESSMENT OF SILICON-CARBIDE AS A POTENTIAL WALL PROTECTION MATERIAL FOR FUSION-REACTORS

The main aspect concerned is the limit of allowable heat load. Radiation-cooled small tiles of three different SiC types were used to determine the critical heat flux density in a gas burner equipment. Extrapolation of the measured data distribution to low failure probability of about 10-3 resulted in a attainable range of 0.7-0.8 MW/m2. Concerning the thermal shock resistance of SiC plates under plasma disruption conditions, literature data suggest that heat pulses of about 2 MJ/m2 could be endurable. Relevant material properties deteriorate under neutron irradiation. There is a large decrease of the thermal conductivity which, however, recovers for the most part at high operation temperature (> 1200-degrees-C). The reduction of the bending strength was measured on samples of various SiC types which had been irradiated to neutron fluences in the range from 5 x 10(24) to 3.5 x 10(26) n/m2 (E > 0.1.MeV) at temperatures of about 500, 1150 and 1500-degrees-C. At fluences greater-than-or-equal-to 3 x 10(25) n/m2 the ultimate bending strength was generally reduced, down to about 50% of the initial level. The Weibull modulus decreased simultaneously to a range less-than-or-equal-to 5. The inadmissibly large reduction of the fracture strength is the crucial point, which is accentuated by the aggravating effect of irradiation-induced helium production in sample materials.