other hand, drastic decrease of leaching of cesium was identified under carbon dioxide exposure. From XRD analysis, formation of calcite was identified. In addition, by using microscopic analysis such as EPMA, SEM-EDX, and Polarization Microscopy, it was found that crystal comprised of calcium grew around the ash particles. It deemed that newly formed calcite inhibited the leaching of Cs by covering reactive surface of bottom ash. In both wetting-drying and freezing-thawing condition, leaching of Cs increased initially. But it decreased after several weeks then it became lower than blank finally. This decrease of leaching also seems to be caused by formation of calcite. The leaching inhibition effect by calcite kept stable when pH is kept above 8. Generally, pH in bottom ash layer is in the range of alkali. Therefore, it is thought that this inhibition effect keeps functioning for a long term.

To estimate the long term leaching of cesium from incineration bottom ash, which is disposed of into normal non-hazardous landfill, is an urgent issue because most of the real bottom ash contains less radio cesium and satisfies criteria set by the government. It is already known that most cesium in bottom ash is hardly-soluble. But its long term stability has not yet clearly been elucidated. For this purpose, pH dependence test was performed to understand leaching behavior of hardly-soluble cesium. To simulate results of pH-dependence test, geochemical model was applied. However, the results were not appropriately reproduced. It was found that cesium is mainly contained in glassy amorphous phase by the research conducted by co-investigators. So, cesium leaching was deemed to be dominated by dissolution of amorphous silicate phase. In order to express the dissolution of silicate phase, Grambow's theory was employed and parameters of it were experimentally determined. By using coupled model of silicate dissolution model, geochemical model, and landfill simulator, long term cesium leaching was estimated. As the results, leaching of cesium is dominated by silicate dissolution and its leaching rate is very low. Cumulative leaching amount of cesium was only 0.1% of the initial content after 60 years.

In this research the environment of landfilled incinerated residues contaminated by radioactive cesium is focused. Behavior of radioactive cesium in landfilled incinerated residues could be affected by temperature and gas composition in the landfill layers. An active semi-aerobic landfill in a cold region and a closed offshore landfill in a mild climate region have been investigated in terms of landfill gas and temperature distributions. Through those investigations, high temperatures in excess of $ 50\ °C $ and carbon dioxide concentration more than 10% were observed in landfill gas extraction wells of the semi-aerobic landfill because of active aerobic biodegradation and heat generation. Ambient temperature around $ 17\ °C $ , high methane concentration more than 60%, and low carbon dioxide less than 1% were observed in monitoring wells of the offshore landfill because of active anaerobic biodegradation and absorption of carbon dioxide in the residues. Landfilled incinerated residues contaminated by radioactive cesium would be exposed to such environment for several years and more.

The amount of elution cesium by centrifugation method was compared with the amount of elution cesium by leaching test JIS K 0058-1 for recovery efficiency. Moreover, every parameter was changed to clarify the differences of cesium concentrations for each. The changed parameters were initial pHs of the solvent, the ratio of solvents and ash, the residence time, the centrifugal force and the centrifuging time. As a result, centrifugation method has the advantage compared to the leaching test JIS K 0058-1 in the working time and the amount of using water. The following conditions were the appropriate conditions from the results. Initial pHs of the solvent had no effect to the