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Mutual separation of Am/Cm/Ln by the use of novel-triamide, NTAamide and water-soluble diglycolamide

新規抽出剤のNTAアミドと水溶性DGAによるAm/Cm/Ln相互分離

佐々木 祐二; 津幡 靖宏; 北辻 章浩; 須郷 由美; 白数 訓子; 森田 泰治

Sasaki, Yuji; Tsubata, Yasuhiro; Kitatsuji, Yoshihiro; Sugo, Yumi; Shirasu, Noriko; Morita, Yasuji

高レベル廃液中のAm/Cm/Ln相互分離はその後燃料製造、核変換することで、資源有効利用や環境負荷低減を導く。しかしながらこれら元素は化学的挙動が酷似し、相互分離は困難とされる。我々はAn/Ln分離に有効なソフト配位原子の窒素を包含するNTAアミドを開発し、その分離性能を明らかにした。また、これと水溶性のTEDGAを溶媒抽出に同時に利用することで、Am/Cmに高い分離比を示すことも明らかにした。ここでは、これらの結果についての詳細を報告する。

Mutual separation of Am, Cm and lanthanides (Ln) is important to develop the partitioning process of high-level radioactive liquid waste, because the application to their different disposal methods are advantageous. Namely, Am is studied for transmutation due to the reduction of long half-life radionuclides, Cm should be kept in interim storage in order to reduce the calorific value, and Ln should be present in the vitrified radioactive waste toward the geological disposal. However, this mutual separation method is difficult to establish because they have very similar chemical behavior, same oxidation state (III) and similar ionic radii. The development of their mutual separation is termed as the challenging study. In order to obtain the satisfactory results, the property of extractant requires the differentiation of actinide (An) from Ln, high preferability to different ionic radii between Am and Cm, and high extractability to hard acids. Therefore, the extractant have to include both N atom, whose soft donor has high selectivity between An and Ln, and O atoms for the strong extractability to An. The new extractant, NTAamide (N,N,N',N',N'',N''-hexaoctyl-nitrirotriacetamide) is a triamide having N donor at the center of backbone, then NTAamide has hybrid performance of complexation to metals by soft N and three hard amidic O atoms. It is clear that NTAamide can extract trivalent An at diluted HNO$$_{3}$$ with small D(Ln), the separation of An from Ln can be carried out at that condition. The SF of Am/Cm by NTAamide is approximate 1.8, which is not so high to separate each other. The combination of NTAamide of extractant and TEDGA (N,N,N',N'-tetraethyl-diglycolamide) as a masking agent in the aqueous phase shows very high SF(Am/Cm) of maximal 6.5. It is obvious that NTAamide is a promising extractant to achieve the mutual separation among Am/Cm/Ln.

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