ACTIVITIES OF WATER AND NITRIC-ACID IN SIMULATED REPROCESSING WASTE SOLUTIONS

Simulations were carried out for thermodynamic activities of water and nitric acid in simulated reprocessing solutions under a high level li quid waste (HLLW) evaporation condition. A prediction method based on a ''Hydration Model'' was developed to evaluate the activity coefficie nts of nitric acid and water in nitric acid solutions containing fissi on products. Suitability of the ''Hydration Model'' was confirmed; the changes in activity coefficient were well explained. Models predictio ns agreed well with the reported experimental results for changes of n itric acid concentration in the HLLW solution during the evaporation c oncentration process. The calculated activities of water and nitric ac id were constant during the concentration process, except for the init ial transient stage. Therefore nitric acid concentration changes shoul d not have significant effects on chemical reactions, such as precipit ation or volatilization, in the solution during HLLW concentration.