### 7. 英文概要 (Abstract of this research)

It is very important to manage the wastes polluted with radioactive Cs emitted at the accident of Fukushima Daiichi Nuclear Power Plant. Thermal treatments, such as incineration and melting, must be very effective to reduce the volume of the polluted wastes and stabilize them. We especially focus on melting treatment plant and analyze the movement of Cs in the treatment process and try to make clear the effectiveness of each treatment system. We also try to find whether thermal treatment can be effective for the treatment of polluted soil, and security condition of labors of such a treatment facilities. For those purpose, we carried out the following four research issues and got the result of each issue.

### Research issue No.1: Estimation of the amount of wastes or materials from wastes for thermal treatment and investigation on the optimal treatment system

We made the treatment system model of Fukushima city and Kyoto city for the estimation of quantity of wastes and its concentration of radioactivity. Based on the total cost of the treatment including disposal, usage of existing facilities is expected to be most effective. If disposal of treated wastes is carried out following the guideline of Ministry of Environment, treatment system which does not make high level radioactive materials from waste is supposed to be most effective.

Research issue No.2 : Behavior of cesium in waste incineration and melting process and conditions for cesium separation, concentration and containment.

In this issue, the behavior of stable cesium in flue gas was investigated at waste thermal treatment plant and the combustion and melting behavior of cesium were experimentally studied. As the results, over 99.7% of the stable cesium in flue gas at waste thermal treatment facilities could be removed by air pollution control including the bag filter. The mass of stable and radioactive cesium in the bottom ash was tended to decrease with higher air ratio and combustion temperature. The stable cesium in model ash with NaCl as chlorine source could be highly vaporized and removed. However, the vaporization and leaching enhancement effect of NaCl could be inhibited by $ Fe_{2}O_{3} $ , MgO and $ P_{2}O_{5} $ . The addition of $ Al_{2}(SO_{4})_{3} $ to sample could not contain the cesium in slag.

Research issue No.3: Study on the effectiveness of thermal treatment for decontamination of radioactively polluted soil.

When soil polluted with radioactive Cs is heated to 600 degree, more Cs became adsorbed to larger size soil particles. It also became clear that dissolution of Cs from soil particles decreases when it is treated by about 500 degree C. Therefore, thermal treatment of soil or decontamination wastes at 500 to 600 degree C is expected to be effective to reduce their volume and stabilize them.

### Research issue No.4: Risk assessment of labors and establishment of safety operation manual

Risk assessment of workers about internal and external radiation exposure was carried out in two incineration plants, A and B. Considering the effects in various kinds of place, we conducted the measurement by using personal dosimeters. We also measured the concentration of particles in the air depending on place of the facilities. The results showed that external dose was lower than that of the ambient air, and we could not detect the $ \gamma $ rays from collected particles, which means that it seems enough to use the safety manual for dioxines to prevent the internal exposure.