The recycling of spent nuclear fuel is a strategic mission for the CEA aimed at improving the sustainability of the fuel cycle and reducing the impact of radioactive waste. In this context, zirconium has been identified as one of the most problematic fission products in the PUREX process due to its complex chemistry in nitric medium. It is involved in co-extraction phenomena, the formation of interfacial cruds, the degradation of contactor hydrodynamic performance, and the reduction of decontamination factors.
The objective of this PhD thesis is to develop a selective zirconium precipitation step directly within the dissolution liquor prior to liquid-liquid extraction. The central scientific challenge is to understand how to control the selectivity of this precipitation in a highly nitric and complex medium.
The proposed approach is based on the use of a precipitating agent adhering to the CHON principle. The work will first focus on single-metal systems and subsequently on mixtures representative of dissolved fuel, in order to identify competitive phenomena between elements.
The expected results pertain to the understanding of precipitation mechanisms, the identification of parameters governing process selectivity, and the demonstration of quantitative zirconium removal without significant actinide loss. This approach could lead to a more robust PUREX process, better suited to high-burnup fuels. The PhD candidate will develop expertise at the interface of coordination chemistry, separation chemistry, and nuclear process engineering, within a research environment of high scientific and industrial impact featuring an extensive array of characterization techniques.