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Study on degradation properties of NBP precipitant by $$gamma$$-ray irradiation

$$gamma$$線照射によるNBP沈殿剤の劣化特性の研究

野上 雅伸*; 杉山 雄一*; 川崎 武志*; 原田 雅幸*; 川田 善尚; 森田 泰治; 菊池 俊明*; 池田 泰久*

Nogami, Masanobu*; Sugiyama, Yuichi*; Kawasaki, Takeshi*; Harada, Masayuki*; Kawata, Yoshihisa; Morita, Yasuji; Kikuchi, Toshiaki*; Ikeda, Yasuhisa*

FBR燃料用高度化沈殿法再処理システム開発の一環として、U(VI)のみを選択的に沈殿させる第1沈殿工程の候補沈殿剤である$$N$$-$$n$$-ブチル-2ピロリドン(NBP)の$$gamma$$線照射に対する耐久性を、硝酸濃度をパラメーターとして検討した。硝酸濃度3Mにおいては、照射に伴うNBPの残存率は硝酸濃度によらず線量増加とともに直線的に減少し、1MGyの照射で約20%が分解した。一方、6M硝酸水溶液においての劣化は顕著であり、0.1MGyの照射で約30%が分解することがわかった。NBPの劣化機構について検討したところ、照射によりNBPのピロリドン環に酸素原子が付加して開環し、さらなる酸素原子の付加により低分子化が生じ、複数の鎖状モノアミドやC4化合物を経てシュウ酸が生成・蓄積することが明らかとなった。

As a part of the development of a novel reprocessing system for spent FBR fuels based on the precipitation method, influence of concentrations of HNO$$_{3}$$ on the stability by $$gamma$$-ray irradiation was examined for $$N$$-$$n$$-butyl-2-pyrrolidone (NBP), a candidate precipitant for the first precipitation step for selectively precipitating U(VI). The residual ratios of the samples for HNO$$_{3}$$ solutions up to 3 M were found to be decreased identically, where ca. 20% of NBP was degraded after the irradiation of 1 MGy. It was found that the degradation of the samples of 6 M HNO$$_{3}$$ is more distinguished, where ca. 30% was degraded after the irradiation of 0.1 MGy. As the result of the investigation of the degradation mechanism of NBP, it was revealed that the degradation started from the cleavage of the pyrrolidone ring of NBP by the addition of oxygen atom, followed by the formation of chain monoamides and C4 compounds by the continuous addition of oxygen, leading to the generation of oxalic acid.

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