In situ XAFS measurement of uranyl-amide complexes under UV-lamp irradiation

Suzuki, Shinichi; Kobayashi, Toru ; Shiwaku, Hideaki   ; Yaita, Tsuyoshi

In our group, an innovative chemical separation process is proposed for the recovery of all actinide from spent nuclear fuel. One of the main purposes of this process is selective isolation of uranium with branched alkyl type N,N-dialkyl-monoamide(BAMA). Since BAMA has the steric hindrance on the complexation with metal cations, BAMA can be used to separate An(VI) from An(IV). One of BAMA, N,N-di-(2-ethyl)hexyl-(2,2-dimethyl)propanamide (DMPA), can recover U(VI) selectively without accumulating Pu(IV) in uranium isolation process. The structural parameters of uranium(VI)-BAMA were determined by XAFS to elucidate the mechanism of selective separation of uranium(VI). The obtained bond distance between uranium(VI) and oxygen of DMPA is 2.31 A. In case of Th(IV)-DMPA complex in ethanol, DMPA could not coordinate with Th(IV). The components of first coordinate sphere of Th were oxygen atoms of four nitrate anions and water molecules. The U(VI) isolation manifested only in BAMA extraction system. In the presentation, we will show the results of in situ XAFS measurement of U-amide (and/or TBP) complexes on uranium valence change by Xe-lamp irradiation in order to evaluate U(VI) selectivity.