Fundamental study on hydrogen production by radiation related to material properties of boron-containing geopolymers with reduced water content

Abstract

ABSTRACT We investigated the radiolytic hydrogen production of geopolymers that are a candidate material for solidifying radioactive waste. The effects of water content and solid properties on the hydrogen production were evaluated by 60Co γ-ray irradiation using geopolymers with and without boric acid, which controls the setting time of the geopolymer. We also constructed a preliminary model of the geopolymer pore structure and calculated the dose to water on the pore surface using Monte Carlo simulation. Hydrogen production was influenced by water content, specific surface area, and electron density of elements in the solid, and increased as these values increased. Simulation results suggested that the amount of hydrogen was affected by the dose of Compton electrons generated by γ-ray irradiation on the geopolymer solid to water on the pore surface. The apparent hydrogen production yield of the geopolymer containing boric acid was 1.1 × 10−8 mol/J, less than 1/4 of that of water. When this sample was heated over 800°C, it decreased to 1.0 × 10−9 mol/J. In contrast, the apparent hydrogen production yield based on the energy absorbed by water in the geopolymer was larger than that of water and increased with a decrease in water content. Furthermore, it decreased below 0.2 wt.% water content.