| Popis: |
Powder of Na2B4O7, a simulated low-level radioactive waste concentrate discharged from PWR power plants, was successfully immobilized into a borosilicate glass matrix by hydrothermal hot-pressing. Waste forms with high waste contents up to 55_??_ were produced. Addition of Ca(OH)2 to a starting powder reduced leachability of waste forms. Solid powder of Na3PO4·12 H2O gave water which was essential to the solidification by hydrothermal hot-pressing. The optimum conditions to produce a waste form with high mechanical strength and low leachability, were determined as follows; reaction temperature: 350°C, reaction pressure: 21 MPa, reaction time: 10 min, heating and cooling rate: 1°C/min. The waste form with 35_??_ waste content produced under the optimum conditions, had high density (2.44 g/cm3), high volumetric reduction (product/waste=1/2), high compressive strength (240 MPa), low leachability (11 g/m2·d determined by leach tests at 40°C for 28 d in deionized water) and high thermal stability (not melted below 600°C). It was shown that a large waste form with 30_??_ waste content, 30 cm in diameter, was successfully produced by hydrothermal hot-pressing. |
