APPLICATION OF HYDRATION MODEL TO EVALUATE GAS-PHASE TRANSFER OF RUTHENIUM AND TECHNETIUM FROM REPROCESSING SOLUTIONS

In order to evaluate the amounts of gas phase transferred ruthenium (R u), and technetium (Tc), simulations were made for the continuous evap orator used in a reprocessing plant to concentrate high level liquid w aste. The concentrations and activities of nitric acid and water, whic h controlled the reaction rate and gas-liquid equilibrium in the evapo rator solution, were evaluated using the previously developed ''Hydrat ion Model''. When the feed solution contained 2.7 M (=mol/dm3) of nitr ic acid, the nitric acid concentration in the evaporator solution reac hed its maximum at the concentration factor (CF) of 6 (CF: concentrati on ratio of FPs in evaporator and feed solutions). The activities of n itric acid and water were saturated at values of 0.01 and 0.43, respec tively, after the CF reached 6. The simulation predicted decontaminati on factors DFs of 2 x 10(5) and 8 x 10(3) for Ru and Tc, respectively, for a typical evaporation conditions with an operational pressure of 6,700 Pa, and FPs of 0.02 to 1.4M. The simulation results agreed with the verification experiment, which will be described in next paper, wi thin a factor of 2 for the amount of gas-phase transferred Ru during e vaporation. The factor for the amount of gas-phase transferred Tc was estimated as 5 from the measurement error in the gas-liquid equilibriu m constant.