Development of partitioning method

A partitioning method has been developed under the concepts of separation of nuclides in high level nuclear fuel reprocessing liquid waste according to their half lives and radioactive toxicity and of disposal of them by suitable methods. In the partitioning process, which has been developed in JAERI, adoption of solvent extraction process with DIDPA (di-isodecyl phosphoric acid) has been studied for actinides separation. The present paper mainly describes studies on back extraction behavior of Np(IV), Pu(IV) and U(VI) in DIDPA. Most experiments were carried out according to following procedure. These actinides were extracted from 0.5 M nitric acid with DIDPA, where nitric acid concentration in HLW is expected to be adjusted to this value prior to actinides extraction in the partitioning process, and back-extracted with various reagents such as oxalic acid. The experimental results show that distribution ratios of Np(IV) and Pu(IV) can be reduced to less than unity with 1 M oxalic acid and those of U(VI) and Np(IV) with 5 M phosphoric acid. From results of these studies and previous research on Am and Cm, following possibilities were confirmed ; U, Pu, Np, Am and Cm, which are major actinides in HLW, can be extracted simultaneously with DIDPA, and they can be removed from DIDPA with various reagents. (nitric acid for Am and Cm, oxalic acid for Np and Pu, and phosphoric acid for U respectively). (author)