Volatilization of Technetium from Simulated Reprocessing Solutions

概要

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Volatilization behavior of technetium was investigated in order to evaluate the decontamination efficiency of an evaporator for reprocessing waste solutions. The gaseous species of technetium volatilized over HTcO4 solutions had been considered as the mixture of Tc2O7 and HTcO4. Estimation of the decontamination efficiency needs to determine whether the dominant gaseous species is Tc2O7 or HTcO4. The continuous dis-tillation of dilute HTcO4 solution was carried out and we obtained the purification factor (PF) defined as the concentration ratio of technetium in the concentrate and distillate. The PF was normalized by total pressure, HTcO4 molarity and mole number in 11 solution. The normalized PF was reciprocal to the second power of HTcO4 molarity and was proportional to the activity of water. These findings suggested the dominant gaseous species were Tc2O7 and volatilization was the dehydration of HTcO4 forming gaseous Tc2O7. The vapor pressure of Tc2O7 was obtained from PF and the equilibrium constant of volatilization reaction was calculated considering that the gaseous species was dominantly Tc2O7. The thermodynamic functions con-trolling the volatilization reaction were obtained from the dependence of equilibrium constant on temperature as, ΔH=82.3 kJ•mo;-1 and ΔS=205.4 J•mo;-1K-1, respectively.
社団法人日本原子力学会の論文
1996-09-25