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

在这个项目中，我们研究了以下两个课题，这是使我们建议的等离子体去污工艺可行所必需的。(1)利用实际常压等离子体演示等离子体去污过程。(2)制定工艺安全评价方法，对其工艺安全进行评价。在前一课题中，我们利用稀有气体和CF_4/O_2混合物生成常压非平衡等离子体，并进行了去除不锈钢板表面氧化钴膜的实验。根据放电条件的不同，产生的常压非平衡等离子体有常压辉光放电和介电燃烧器放电两种工作模式。明确了各种模式和各种条件下的去污特性。在Mel CF_4/O_2混合气体等离子体中，氟化反应在180-200℃充分进行，几乎所有的钴氧化物在5分钟内转化为其氟化物。氟化物可以很容易地被水冲走，这表明了该工艺实际应用的可能性。在后一主题中，我们对细颗粒的产生及其生长过程进行了建模，并加入了等离子体过程中金属的蒸发。并编制了模拟等离子体过程中出现的一系列过程的数值计算程序。利用该程序计算了等离子体过程中产生的细粒子的特性。通过在其代码中加入各种空气过滤器的收集过程，此外，我们完成了一系列的过程，用于估计过程，估计未收集的细颗粒释放到环境中的数量。因此，我们可以开发一种方法来获取等离子体去污技术的安全性评估信息。

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.