TRANSFER OF RUTHENIUM FROM A SIMULATED REPROCESSING SOLUTION TO GAS-PHASE DURING A CONTINUOUS DISTILLATION

A continuous evaporation experiment was carried out, in order to verif y the ruthenium (Ru) volatilization mechanism, for a simulated high-le vel liquid waste (HLLW). The feed solution contained 2.65 M (10(3) mol /m(3)) of nitric acid and 0.097 M fission product compounds (FPs) incl uding 0.008 M RuNO3+. The operation pressure was 12,700+/-200 Pa and t he operation was continued for 44 h. The total volume of the feed solu tion was 13.0x10(-3) m(3) and the volume of the final evaporator solut ion was 0.90x10(-3) m(3). The concentration ratios of elements in dist illate to concentrate initially decreased with the evaporator operatio n. Then the ratios reached plateau for Cs and Ce, with values of about 7x10(-7). The ratio for Ru was 200% of those for Cs and Ce at 15 h af ter the operation began, and decreased to 110% toward the end of opera tion. The difference in ratios was quantitatively explained by the for mation rate of volatile Ru in simulated HLLW solution taking into acco unt the changes of activity and concentration of nitric acid caused by salting out effect of FPs.