Sulfurization of rare-earth oxides in simulated spent fuel

模擬使用済燃料中の希土類酸化物の硫化

篠原 元輝*; 佐藤 修彰*; 桐島 陽*; 杤山 修*; 佐藤 宗一 

Shinohara, Genki*; Sato, Nobuaki*; Kirishima, Akira*; Tochiyama, Osamu*; Sato, Soichi

使用済燃料からウランを回収するために、硫化を利用した再処理方法を提案した。このプロセスは、使用済燃料をボロキシデーションし硫化した後に、磁気分離あるいは選択溶解する工程からなる。今回は、希土類酸化物(RO)のCSを用いた硫化挙動について述べる。模擬使用済燃料中の(RO)の選択的硫化反応について試験を行い、結果を熱化学的に考察した。NdとEuの酸化物はCS, 500Cの雰囲気で選択的に硫化され、NdS, EuSとなった。一方、ウランはUOのまま残った。硫化温度と時間についても評価した。

For the recovery of uranium from spent nuclear fuel, the sulfide reprocessing process has been proposed. The process consists of voloxidation and sulfurization steps followed by either magnetic separation or selective leaching steps. In this process, selective sulfurization of the rare-earth elements is applied, while the uranium oxide remains unreacted. The sulfurization of rare-earth oxides RO (R=Nd, Eu) was examined using CS, and found that they formed oxysulfide and sulfides even at temperatures lower than 500C. From the results of the sulfurization of RO in the simulated spent fuel, it was found that RO for Nd and Eu were selectively sulfurized by CS at 500C forming NdS and EuS, respectively, while uranium remained as UO. Effects of sulfurizing temperature and time were also investigated and compared with the results of thermodynamic consideration.