### 8. 英文概要

The behavior of cesium was investigated in waste material as a function of waste type and combustion conditions. Samples used in the experiments were of 5 types of wastes such as RDF (2 types), RPF, wood chips derived from demolition waste, and sewage sludge. After stable cesium was added to respective wastes, they were combusted in a lab-scale electric furnace and a pilot stoker type incinerator at Takuma research facility. A cesium residual rate (RCs) in combustion residue was defined by the following equation $ [RCs = (\text{amount of insoluble cesium in the residue}) / (\text{additional amount of cesium})] $ . As a result, it was found out that RCs differed depending on the types of wastes in both laboratory and pilot tests (RDF: 5-20%, RPF: 30%, wood chips: 30%, sewage sludge: 85%).

As an effort to deal with the huge amount of radioactive incineration ash, we investigated cesium chemical form which is supposed to be one of the main radioactive elements in the disaster zone. Because the incineration ash from the Fukushima disaster area contains little amount of cesium, we used the Cs-rich simulated samples synthesized by Takuma. We artificially added a large amount of non-radioactive cesium compounds in some pretreated wastes such as RDF, RPF and wood chips in order to produce some samples which are supposed to facilitate the investigation about the chemical form of cesium. We conducted a series of experiments to investigate the chemical form of cesium including XRF, XRD, SEM-EDX, sieving test, etc in the simulated incineration bottom ash.

Through our research, we found that cesium exists as CsCl in the fly ash and there should be no or very little amount of cesium accumulated in the mineral phases of the simulated bottom ash. Using SEM-EDX analysis, we found that cesium is unevenly distributed in some parts of the glass phases at various concentrations and also distributed in some kinds of minerals as well. Besides, cesium behavior resembles that of potassium in most areas according to our observations by using SEM-EDX analysis. Finally, by sieving test we noticed that there is a clear tendency in chemical composition from coarser to finer particle size, indicating that cesium is highly enriched in the finer fractions based on our bulk analytical results (XRF).

In order to clarify the characteristics of Cs leaching from incineration residues, sequential extraction and seval leaching tests at different pH, temperature, cation concentration, organic concentration were conducted using incineration residues of artificially prepared wastes with a stable Cs salt and actual ash (radioactive Cs non-contaminated incineration ash). Behavior of Cs fraction of the artificial incineration ash was almost similar to that of the real ash. Each fraction of Cs was similar to that of K. Cs in residual fraction would be present with Fe and Al. The effects of pH and temperature on Cs leaching rate from the artificial incineration ash were little under actual landfill condition (pH>5 and tepmperature<60 $ {}^{\circ} $ C). K and Na over 5,000 mg/L increased Cs leaching rate. Cs leaching rate at added K concentration of 10,000mg/L was 1.3 times higher than that of no K additives. Therefore, it was recommended that no high salt contained waste such as fly ash should be landfilled over incineration ash. Acetic acid and humic acid scarcely increased Cs leaching rate; on the contrary, these decreased Cs leaching rate for some artificial incineration ash.

Phase transformation and leaching of cesium from incineration bottom ash were investigated by conducting accelerating weathering experiment. Four kinds of weathering conditions were set; namely, blank (under nitrogen gas condition), wetting and drying, freezing and thawing, and exposure to carbon dioxide gas. Leaching of cesium under blank conditions didn't change. On the