Development of Radio-Active Waste Decontamination Process by Using Atmospheric Pressure Plasma and Its Safety Analysis.

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In this project, we have studied the following two subjects, which is required to make the plasma decontamination process, which we have suggested, practicable. (1)To demonstrate the plasma decontamination process by using practical atmospheric pressure plasma. (2)To develop the process safety assessment method and to assess its process safety.In the former subject, we generated the atmospheric-pressure non-equilibrium plasma by using rare gases and CF_4/O_2 mixture and we carried out some experiments of removal of cobalt oxide film stained on the stainless steel plate surface. The atmospheric -pressure non-equilibrium plasma generated here had two operation modes, atmospheric pressure glow discharge and dielectric burner discharge, depending on its discharge conditions. The decontamination characteristics under each mode and various conditions were made clear. In the case of Mel CF_4/O_2 gas mixture plasma the fluorination reaction proceeds sufficiently at 180-200 degree C and almost of cobalt oxide was converted into its fluoride within 5 minutes. The fluoride could be flush out easily by water and it could indicate the possibility of practical use of this process.In the latter subject, we made modeling of processes of fine particle generation and its growth, adding to the evaporation of metal, which takes place in the plasma process. And also we developed the numerical calculation code to simulate a series of process which appears in the plasma process. By using this code we calculated the characteristics of fine particles generated in the plasma process. By adding to its code a collecting process by various air filter, furthermore, we completed a series of the process for the estimation process estimate the amount of fine particles which were released into the environment without collecting. Consequently, we could develop a method to obtain information fo safety assessment of the plasma decontamination technique.