Hydrothermal immobilization of glass powder containing simulated high level radioactive waste

The lithification of borosilicate glass powder containing simulated high level radioactive waste with the hot pressing technique under hydrothermal conditions was investigated. The glass powder was easily formed to hardened body with a little distilled water (5 ∼ 10 w/o). This glass body showed a high compressive strength above 2,500 kg/cm². The lithification occurred at 240 ∼ 270℃ with the rapid shrinkage. The initial shrinkage kinetics were examined in consideration of the dissolution core model: 1-(1-x)^1/3 = kt^1/2, 1-(1-x)^1/3 = k't, where x is the shrinkage ratio, k and k' the constants and t the reaction time. The apparent activation energy of shrinkage below 250℃ was found to be about 20 kcal/mol, which was good agreement with that of the growth of surface reaction layer in hydrothermal solution. It was suggested that the initial stage of lithification followed the dissolution-deposition model. (author)