Abstract
Thermal insulation materials for core support of VHTR, planned by JAERI, must have moderate compressive strength and dimensional stability besides low thermal conductivity, because it must sustain weight of reactor core. As it is not replaceable during a life of the reactor, it must be stable both mechanically and physically at service temperature of max. 1, 100°C for 20yr. For selection of the materials, we investigated properties of some candidates, namely some kinds of carbon, silicon nitride and fused silica, and evaluated their feasibility.Some preliminary tests, heat treatment tests and compressive creep tests for 1, 000h at 900 and 1, 000°C were carried out.(1) In the preliminary tests, EG-38B (carbon baked at 1, 350°C) and Fine Finnex 600 (silicon nitride) showed acceptable physical stability.(2) In the heat treatment test of silicon nitride, weight loss of specimens was observed, which was probably due to thermal decomposition.(3) Compressive creep deformation of Fine Finnex 600 was negligible at stress of 100kg/cmcm2 for 1, 000h. Heat treatment at 1, 200-1, 300°C for 50h improved dimensional stability of carbon at 1, 000°C.
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