Volatilization of Technetium from Simulated Reprocessing Solutions

抄録

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.