Recent progress on development of the pyrochemical process of spent nitride fuels for MA transmutation

MA核変換用窒化物燃料の乾式処理技術開発の進捗

林 博和 ; 佐藤 匠  

Hayashi, Hirokazu; Sato, Takumi

加速器駆動システム(ADS)を用いたマイナーアクチノイド(MA)核変換用の燃料として原子力機構において研究開発が行われているウランを含まないMA窒化物燃料の乾式処理技術開発の進捗を紹介する。その内容は、窒化物燃料乾式処理の主要工程の装置開発に関するもので、溶融塩電解における陽極溶解速度を向上させるための陽極構造の改良、及びCd電極に回収した超ウラン元素の再窒化試験を100グラムCd規模で実施する装置の製作についてである。本講演では、これらの装置等の特徴、及び性能評価のためのコールド模擬物質を用いた試験結果について報告する。

Transmutation of long-lived radioactive nuclides including minor actinides (MA: Np, Am, Cm) has been studied in Japan Atomic Energy Agency (JAEA). Pb-Bi cooled sub-critical accelerator-driven system (ADS) is regarded as one of the powerful tools for transmutation of MA under the double strata fuel cycle concept. Uranium-free MA-Pu nitride fuel was chosen as the first candidate for MA transmutation. Reprocessing of spent ADS fuel and reusing MA recovered from the spent ADS fuels is necessary to improve the transmutation ratio. A pyrochemical process has been proposed as the first candidate for reprocessing of the spent nitride fuel for MA transmutation. Main process of the proposed pyrochemical treatment of nitride fuels consists of molten salt electrorefining and renitridation of actinide elements recovered in Cd cathode. Recently, we have proposed an innovative anode concept to improve anodic dissolution rate on the electrorefining process; a large electro-conductive crucible is used as an anode crucible. Applicability of this concept has been verified by confirming high anodic current on the experiments using surrogate materials such as DyN pellets. As for renitridation process, an apparatus with 100g-Cd scale cold tests has been designed and manufactured. Suitable conditions of the renitridation process (via nitridation-distillation method) with the scale-up apparatus are being studied using surrogate materials such as Dy-Cd alloy.