Thermal analyses of beryllide pebbles in water vapor atmosphere as advanced neutron multipliers

Highlights: • Binary beryllide pebbles were successfully fabricated by the novel process. • The beryllide pebbles indicated much more resistant to water vapor and lower H2 generation rate than Be pebble. • With regard to thermal expansion, the beryllide blocks exhibited lower CTE than Be block. - Abstract: The safety of the water coolant solid breeder blanket of a fusion reactor has become one of the most critical issues. In particular, Be pebbles as a multiplier material have been well-known to generate hydrogen and exothermally react while reacting with water vapor at high temperature. Unlike these Be pebbles, beryllium intermetallic compounds (i.e., beryllides) are one of the most promising materials because of their significantly higher chemical stability. Beryllides pebbles have been successfully fabricated by a number of approaches developcombining plasma sintering synthesis and rotating electrode granulation methods Thus, as-received Be₁₂Ti pebbles (consisting of Be, Be₁₂Ti, and Be₁₇Ti₂ phases), homogenized Be₁₂Ti pebbles, and as-received Be₁₇Ti₂ pebbles have been successfully fabricated. The oxidation, hydrogen generation, and thermal expansion properties of these pebbles were investigated and compared with those of the reference Be pebbles. Beryllides pebbles were significantly more resistant to oxidation by H₂O while generating lower amounts of hydrogen as compared to Be pebbles. Among these beryllides pebbles, homogenized Be₁₂Ti pebbles and as-received Be₁₇Ti₂ pebbles showed lower weight gain and hydrogen generation than as-received Be₁₂Ti because the latter contained some fractions of Be phase inside the pebbles. With regard to thermal expansion, it was obvious that the beryllides exhibited lower coefficients of thermal expansion (CTE) than Be.