低レベル放射性雑固体廃棄物処理へのプラズマ溶融法の適用性評価 溶融固化体の物性と溶融時の核種挙動に与える炉内雰囲気ガス条件の影響

Abstract

For evaluating the possibility of applying a thermal plasma method to treatment of low level miscellaneous solid wastes, the effect of heating atmospheric gases on the material properties of the treated waste forms and the behavior of radionuclides were examined by conducting plasma melting tests of simulated miscellaneous solid wastes (iron, fly ash and wood) with surrogate nuclides. We found that the material properties of the treated waste forms have a homogeneous distribution of surrogate nuclides and low leaching rate of them: from the slag layers the rate was less than 10-7 (g·cm-2·d-1)and from the metallic layers was less than 10-5 (g·cm-2·d-1) in every atmospheric condition. The compressive strengths of the slag layers obtained in the oxidization conditions were over 50MPa. The migration behavior of Co, Ni, Nb, Sr and Ce was not influenced by the heating atmospheric conditions, and almost 100% of these nuclides migrated to the treated waste forms. Migration rate of Cs to the slag layers was also not influenced by the heating atmospheric gases except under extremely high reductive conditions, and a high residual rate of over 60% was obtained. These results show that a plasma melting method can be used for treatment of miscellaneous solid wastes.