報告書番号

W98016

タイトル（和文）

低レベル放射性雑固体廃棄物のプラズマ溶融時のセシウム蒸発挙動

タイトル（英文）

Vaporization Behavior of Cs in a Plasma Melting Process of Simulated Low-level Miscellaneous Solid Wastes

概要 （図表や脚注は「報告書全文」に掲載しております）

低レベル放射性雑固体廃棄物の処理にプラズマ溶融法を適用するためには，廃棄体の放射能測定において重要な核種であるCsの溶融固化体中への残存率に与える溶融処理条件の影響を解明する必要がある．これまで，Cs残存率に与える廃棄物組成の影響については，加熱条件が一定の場合は塩基度を用いて評価できることを明らかにした．廃棄物重量や加熱出力などの溶融処理条件がCs残存率に与える影響を評価するために，加熱時間に対する溶湯形状の変化と溶融スラグ中のCs濃度を調べ，溶融時のCs蒸発挙動を検討した．試料が全量溶融した後の溶融スラグからのCs蒸発挙動は１次の反応速度式で表すことができた．この時のCsの蒸発速度定数と溶湯形状の経時変化の結果を用いて，試料が全量溶融するまでの過渡的な状態における溶融スラグ中のCs濃度を溶湯形状の経時変化を考慮した式から推定した結果，実測値と一致した．この結果から，溶融処理後のCs残存率は，スラグ形成成分の溶融速度と蒸発速度定数に大きく依存することを明らかにし，廃棄物重量や加熱出力などの溶融処理条件がCs残存率に与える影響をスラグ形成成分の溶融速度から評価できる見通しを得た．

概要 （英文）

In order to apply the thermal plasma melting method to the treatment of low level miscellaneous solid wastes, it is essential to understand the effect of treatment conditions on the migration rate of Cs to the melt because Cs is an important nuclide for evaluating radioactivity in the waste before disposal. It was found in our previous studies that the effect of the waste composition on the migration rate of Cs could be evaluated by using basicity when the heating condition is constant. To establish a method for evaluating the effect of the melting conditions such as waste mass and heating power on the migration rate of Cs, the vaporization behavior of Cs is discussed by measuring the temporal change of molten bath form and concentration of Cs in the molten slag. The temporal change of concentration of Cs in the molten slag was expressed by a first-order type reaction rate formula when the samples were melted completely. The values of concentration of Cs in the molten slag calculated from the rate constant and the result of temporal change of the molten slag form using the rate formula established from the molten bath formation model in a batch melting process were in good agreement with the experimental values. We found that the migration rate of Cs to the slag layers depend on the vaporization rate constant of Cs and the melting rate of the waste components forming slag. This result suggests that the effect of the melting conditions such as amount of inorganic waste materials and heating power on the migration rate of Cs to the slag layer can be evaluated by using the melting rate of the waste components forming slag.

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