THERMAL TESTS ON B4C-OVERLAID CARBON-FIBER-REINFORCED COMPOSITES UNDER DISRUPTION HEAT LOAD CONDITIONS

High heat flux experiments (550-1600 MW m(-2), 2-10 ms) in the JAERI e lectron beam irradiation system (JEBIS) were carried out on B4C-overla id carbon fibre reinforced composites (CFCs), on which the B4C was ove rlaid with a thickness of 50-800 mu m by using three coating methods, chemical vapour reaction (CVR), low pressure plasma spraying and chemi cal vapour deposition. Investigations were made with respect to change s of weight, surface morphology, surface atomic composition and crysta l orientation of B4C. Severe exfoliation and large weight losses of th e B4C layers were observed in the samples except for the sample produc ed by the CVR method. Weight losses of the samples increased with the heat flux under the identical absorbed energy. A preferential evaporat ion of boron was observed only in the melted area of the B4C under low er heat flux conditions (550 MW m(-2), 5 ms), the evaporated thickness was a few micrometres. However, under higher heat flux conditions (16 00 MW m(-2), 2 ms), the atomic ratio of the boron to carbon did not ch ange. The present results suggest that the B4C-overlaid CFCs produced by the CVR method can be applied to the divertor materials of JT-60U.