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One of the aims of next generation closed nuclear fuel cycles is to recycle the minor actinides (Am and maybeCm) alongside the U and Pu that are isolated in the current generation PUREX process. Recycling minoractinides can reduce the radiotoxicity and the heat loading of the wastes for disposal which leads to reductionsin both the size and longevity of the deep geological repository (Taylor et al. 2022). To achieve this, severalnovel processes have been developed, each taking a different approach. Thei-SANEX (innovative selectiveactinide extraction) process, for example, is essentially a “bolt on” to the PUREX process isolating the minoractinides from the PUREX raffinate. However, the GANEX (Grouped Actinide Extraction) process is a radicallydifferent approach to fuel recycling; using C, H, O, N (CHON) based extractants, the bulk of the U is firstremoved from the dissolved fuel before the remaining transuranic (TRU) actinides are removed in a singlesolvent extraction cycle. In the 1st cycle of the GANEX process, 1 M di-2-ethylhexylisobutyramide (D2EHiBA)is the extractant. Presently, the leading option for the 2nd cycle is the so-called EURO-GANEX cycle in which amixture of 0.2 M N,N,N’,N’-tetraoctyldiglycolamide (TODGA) and 0.5 M N,N’-dimethyl-N,N’-dioctylhexylethoxymalonamide (DMDOHEMA) is used in a kerosene diluent. Stripping of the actinides (trace Uand TRU: Np, Pu, Am and Cm) from the 2nd cycle solvent requires an aqueous soluble reagent that isselective for the actinides and displays selectivity for the trivalent minor actinides over the coextracted trivalentlanthanides.Although the GANEX concept has been successfully demonstrated in a hot test using spent nuclear fuel (SNF)from the Dounreay Fast Reactor (DFR) (Malmbeck et. al. 2019) there are still areas where further optimisationis necessary to raise the technology readiness level (TRL), reduce waste volumes and ensure products meetthe required specification. Firstly, fundamental studies provided data to support changes to the originalflowsheet design that culminated in a test of the revised flowsheet using a simulant feed solution. This paperwill present data on small scale batch solvent extraction experiments that were conducted to underpin theflowsheet design in two key aspects:Simplification of the solvent system; previous work has shown that it may be feasible to replace bothTODGA and DMDOHEMA with a modified methylated DGA (Malmbeck et. al. 2017). Therefore,experiments have been performed to evaluate the Pu loading and third phase boundary in the newsolvent system.Replacement of the sulfonated bistriazinylpyridine stripping reagent with an alternative reagent thatmeets the CHON requirements for waste treatment and disposal. Previously, Mossini et al. (2018) haveidentified pytridiol (PTD) as a potential CHON option for selective actinide stripping. Further batch testswere performed with flowsheet levels of Pu to establish optimum conditions for Am stripping andseparation from lanthanides in the EURO-GANEX cycle.Finally, results of a flowsheet test of a revised EURO-GANEX cycle based on PTD, using realisticconcentrations of TRU actinides in a counter-current centrifugal contactor cascade, will be discussed. |
