Fixation of radioactive waste by HHP method

Simulated high-level radioactive waste was fixed into a silica matrix and tritiated water was fixed into glass powder matrix by a hydrothermal hot-pressing (HHP) method. The simulated HLW and the silica matrix were mixed with NaOH solution and then solidified. When the starting powder was solidified at 350degC, and 66 MPa for 6 h by the use of 10N NaOH solution, the solid body with high compressive strength was produced. From the result by modified MCC-1 leach test, the leach rate of Cs and Sr from solid body was much lower than a concrete form but slightly higher than a glass form. Tritiated water was solidified with only glass powder. The amount of tritiated water fixed by HHP was almost the same as fixed by the ordinary cement solidifying procedure. The compressive strength of the body was higher than that of the cement body. (author)