Mathematical modeling in radionuclide migration in cement-waste composition

The intermediate level radioactive wastes produced as a result of the operation of reprocessing plants and nuclear power station are currently being considered for immobilization in a number of possible matrix materials, including cement, bitumen, and plastics. In the storage or disposal of these solidified wastes, some radioactive products may be leached into contacting water and this water might enter into the environment. Therefore, an estimation of the quantities of radionuclides that ca be leached from waste composites is essential in radioactive waste management. At our laboratory, a promising composite for solidification of radioactive wastes has been developed by incorporation of spent ion exchange resin in cement. Leaching of 137 Cs was studied using the method recommended by the IAEA. Transport phenomena involved in the leaching of a radioactive material from a composite matrix into surrounding water were investigated using three methods on theoretical equations. These were: Method I - using a diffusion equation derived for a plane source model, Method II - using a rate equation for diffusion coupled with a first-order reaction, and Method III - in which the leaching data were also analysed by an empirical method employing a polynomial equation. These three methods are compared with respect to their applicability to the 147 Cs leaching data. (authors)