Advancement in evaporation and calcination techniques for radwastes in India

The evaporation technique is very effective in concentrating the volume of the liquid waste and separating the low-activity distillate. Water is removed in the vapor phase leaving behind nonvolatile radioactive content in the solution. Extensive experimental and theoretical investigations were carried out to optimize the design and operation of the evaporators. The experiments revealed that fouling of tubes and scaling increases at higher chemical concentrations. Therefore, for further removal of moisture, dehydration and denitration of the waste, calciners are used. The nitrates are water soluble and corrosive therefore, these are converted into solid oxides. The oxides are granular solids and chemically stable with good heat conductivity. This facilitates uniform mixing and good compatibility with glass matrix. In order to remove moisture, dehydrate, denitrify, and oxidize the heterogeneous waste into a granular product, various types of calcination techniques have been examined. A brief review of state of art and present state of technology is presented in this paper