Development of vitrification procedure for radioactive wastes from nuclear power plants

The process was studied of vitrification of radioactive wastes from nuclear power plants in laboratory and pilot plant experiments. As against the vitrification of high-level wastes which is based on phosphoric acid as being the glass forming component, in the case of intermediate-level radioactive wastes, the phosphate system of glass was abandoned because the highly corrosive effect of phosphates complicated technical implementation, and attention was devoted solely to silicate systems. Two variants have ensued from the development of the vitrification process. The first is a two-step process with previous removal of water by calcination when the calcinate is batched into the melting unit together with glass forming admixtures. The second variant is a one-step process when a thickened paste of wastes and glass forming admixtures is batched into the unit. Up to now, neither of the two variants completely eliminates difficulties with the charging of the material into the furnace, the escape of ashes into the filtration part and the corrosion of the melting vessel. It is, however, possible to reduce these difficulties to minimum by a suitable choice of technological conditions of the process. Briefly described is the development of the equipment, mainly the melting furnace. Equipment with direct electric heating is recommended. (Z.M.)