Investigation of radiolytic degradation and physio-chemical properties of N,N,N',N'-tetraoctyldiglycolamide upon adding N,N-dioctylhydroxyacetamide during trivalent metal ion extraction

Aqueous reprocessing of spent nuclear fuel, the extraction of trivalent actinides and lanthanides from high-level liquid waste (HLLW) is a crucial step in nuclear waste management, which is achieved by solvent extraction of trivalent using DGAs such as N,N,N',N'-tetraoctyldiglycolamide (TODGA). However, TODGA undergoes undesirable aggregation leading to phase splitting at high metal and acid concentration, which can be avoided by addition of suitable phase modifier. Addition of a neutral phase modifier such as N,N-dioctylhydroxyacetamide (DOHyA), was shown to shift the third-phase formation to higher limits. Though, studies on solvent extraction ability, third phase formation behaviour, on TODGA+DOHyA combined system are available, there is a need to explore physical properties of the system such as density and viscosity, and their dependency on absorbed dose and temperature, in order to gain insight on the behaviour of the system when exposed to the radiation emitted by radionuclides. The thermophysical properties such as viscosity and density were measured for the combined solvent phase as well as the individual solvents in n-dodecane diluents as a function of absorbed gamma radiation dose, temperature and composition of the organic phase. Additionally, activation energy, and entropy changes were also estimated. The extraction behaviour was also studied after irradiation and then compared with the results of unirradiated samples. The results obtained from all these are reported in this paper. The study indicated the stable nature of hydrodynamic behaviour of all the systems in n-dodecane with respect to physical properties up to 500 kGy of absorbed gamma radiation dose