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

在本项目中，我们研究了以下两个课题，以使我们所建议的等离子体去污工艺切实可行。(1)用实际的常压等离子体演示了等离子体去污过程。(2)建立工艺安全性评价方法，对其工艺安全性进行评价。在本课题中，我们利用稀有气体和CF_4/O_2混合气体产生常压非平衡等离子体，并对不锈钢板材表面的钴氧化膜进行了去除实验。根据放电条件的不同，产生的大气压非平衡等离子体有大气压辉光放电和介质燃烧器放电两种工作模式。明确了每种模式、不同条件下的去污特性。在Mel-CF_4/O_2混合气体等离子体中，氟化反应在180-200℃进行得很充分，在5分钟内，几乎所有的钴氧化物都转化为其氟化物。在第二个课题中，我们模拟了等离子体过程中细小颗粒的产生和生长过程，以及金属的蒸发过程。并开发了数值计算程序，对等离子体过程中出现的一系列过程进行了模拟。利用该程序计算了等离子体过程中产生的细小颗粒的特性。通过在其代码中添加各种空气滤清器的收集过程，进一步完成了一系列估算过程，该估算过程估计了未收集的细颗粒物排放到环境中的量。因此，我们可以开发一种方法来获得等离子体去污技术的安全评估信息。

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.