ICONE15-10193 Trivalent actinide-lanthanide separation with diglycolamide and a novel aza-amide based extractant

Abstract

New solvent systems have been developed for the bulk separation of trivalent actinides and lanthanides from radioactive high-level liquid waste and their separation from each other. Synthesis of amidic based solvents namely Tetra (2-ethylhexyl) diglycolamide (TEHDGA) for bulk separation and N,N,N',N'-Tetra(2-ethyl hexyl) 3,6-(N'',N'''dibutyl) Diaza-Octane 1,8 diamide (abbreviated as Diaza Diamide DADA) for group separation, at the required purity have been carried out and suitable process for their respective use in actual applications have been developed. For bulk separation of trivalent actinides and lanthanides, inactive scale engineering runs comprising of simultaneous extraction and stripping operations were carried out to establish the process on an engineering scale including reuse of the solvent system. The composition of surrogate high level waste (HLW) used at engineering scale studies corresponds to first cycle raffinate from reprocessing of long cooled Pressurized Heavy Water Reactor(PHWR) fuel with a burn-up of 6,500 MWd/t. Since trivalent lanthanides and actinides exhibits similar extraction behaviour at higher acidity cerium and lanthanum were only used in making surrogate HLW to represent all the trivalent lanthanides and actinides. In-house developed mixer settlers using passive system of mixing were used for these runs. About 300L of surrogate HLW solutions were contacted with solvent over a period of about 10 hours. The results of such repeated trials have shown near total removal of cerium & lanthanum (>99.8 % & 97 % respectively) at A:O ratio 2.5:1 for TEHDGA system. As the distribution coefficient values for trivalent actinide (^<241>Am) is found to be significantly higher than that for trivalent lanthanides, therefore, it is inferred that separation of trivalent actinides along with lanthanides could be feasible using TEHDGA solvent systems. The stripped product of TEHDGA solvent system was spiked with ^<241>Am and ^<152-154>Eu for studies on group separation of trivalent actinide from lanthanides at laboratory scale using DADA. The solvent system constituted as 0.05M DADA + 10% TBP/n-dodecane, has shown a maximum separation factor of 〜30(D_<Am>/D_<La,Ce>) and 〜5.0 (D_<Am>/D_<Eu>) at pH between 2.5 to 3.0. Complete stripping was achieved at 0.5M nitric acid.