Abstract
With the progress of atomic energy industry, the treatment of radioactive waste solutions has become an important problem. As one of the safest and surest methods of the treatment of the solutions, concentration by evaporation is recommended. However, in the case of using a current standard type evaporator, those organic materials in the solutions which are sensitive to heat often decompose on account of their long stay in the evaporators, and excessive foaming and entrainment often produce radioactive condensates, making the process inefficient. This is the reason why the use of a falling film evaporator has been proposed, and the authors manufactured a test apparatus and studied its decontamination capacity, using water and CMC aqueous solutions as Newtonian and non-Newtonian fluids respectively and LiCl as a tracer.
The results are as follows: (1) When the liquid flow rates are 200300l/hr, and vapor mass velocities 1001, 000 kg/m2hr, the decontamination factors are about 105 for the Newtonian fluid, which coincides well with the results previously obtained by one of the authors who used a standard type evaporator, and about 104 for the non-Newtonian fluids. (2) The mean retention time for the Newtonian fluid is about 0.26 sec, and that for the non-Newtonian fluid about 3.2sec, when the liquid flow rate is about 200l/hr.
