Gamma radiolysis studies of N,N-dioctyl-2-hydroxyacetamide: Complexation effect on the stability and implications on the hydrometallurgical extraction performance

N,N-dioctyl-2-hydroxyacetamide (DOHyA) is one of the most important degradation compounds (DCs) of the well-known extractant N,N,N′,N′-tetraoctyldiglycolamide (TODGA), employed for the minor actinide (MA) recovery processes development from spent nuclear fuel. Due to its lipophobicity, DOHyA would not be easily removed from the solvent through simple washing steps. Therefore, it is expected that DOHyA will be accumulated in the recycled TODGA solvent along the operation, but it also may be degraded itself by radiation. In this work, the radiolytic stability of DOHyA and its possible implications on the extraction process performance were studied under different experimental conditions. For that, DOHyA samples in OK (odourless kerosene) and pre-equilibrated with a) nitric acid and b) the expected europium(III) concentration in a real process dissolved in nitric acid, were subjected to gamma radiation (up to 500 kGy) and analyzed. The extraction properties and changes in the composition of the solvent were checked upon irradiation by different techniques: gamma spectroscopy and ICP-MS for the evaluation of the extraction performance; and HPLC-MS to quantify the degradation of the DOHyA samples, but also to identify and quantify its own degradation compounds. The results indicate that the Eu-complexes formed in the organic phase protect DOHyA from degradation by radiation and induce a change in the degradation pathway, highlighting the importance to perform the irradiation of the resulting solutions of the stability studies in the presence of the corresponding metal ions. Moreover, DOHyA, as well as its degradation compounds (DCs), showed a high affinity for different undesirable fission products in these kinds of extraction processes. In consequence, DOHyA and its DCs must be taken into account in the long-term performance of the extraction process, as well as in the development of the cleaning strategies to recycle the TODGA solvent.