Pressure sintering of simulated high level radioactive wastes with glass powders

High level radioactive wastes solutions from the reprocessing of spent nuclear fuel must be transformed into a stable solid forms which are suitable for interim and final-disposal. In this report, solidification of simulated high level radioactive wastes with various glass powders, such as Pyrex, Vycor (porous high silica), and slag glass by hot-pressing was investigated. The optimum hot-pressing temperatures for mixtures of the wastes and Pyrex or the porous high silica glass powders were as low as 650 -- 7500C, this might make solidifying process enable to be carried out at desirable low temperature for prevention of escape of volatile f. p. and the maintenance of plant. The densification behavior of the compacts was controlled by viscous flow of glass phase during hot-pressing. Chemical durability of hot-pressed compacts was determined by quantitative analysis of the amount of alkali leached into hot water by block immersion method and JIS-R-3502. The resultant leach rates of the products were in the range of 10-3-10-5 g/cm2.day, and hot-pressed compacts except for that of slag glass powder showed fairly good resistance against hot water. The mixing by vibro-mill improved pronouncedly the leachability of compacts. However, cristobalite and quartz crystal phases which caused the abnormal expansion at their α-β transition points were detected in the compacts by thermal expansion and X-ray diffraction analyses. The troubles due to crystallization considerably decreased by dispersing the phase of stabilized wastes in glass phase. (auth.)