Hydrothermal reactivity of neutron absorber composites

The stability of neutron absorber composite materials at hydrothermal conditions was tested in a series of two-week experiments to mimic spent nuclear fuel disposal. Coupons, composed of boron carbide (B4C) sintered with and encased in aluminum, were increasingly altered in experiments at 150, 230, and 300 °C and pressures of 150 bar. Alteration of aluminum to boehmite (γ-AlO(OH)) and hydrogen gas generation occurred over the range of investigated temperatures, but is most significant at 300 °C. We found that the formation of boron-bearing mineral phases was not detected; however, aqueous boron was present in the reaction fluids.