[en] The use of single cycle solvent extraction flowsheets and centrifugal contactors are key objectives in the development of advanced processes for spent fuel and waste processing in future closed fuel cycles. These advances lead to intensified processes, reducing the costs of plants and the volumes of wastes arising. By adopting other flowsheet changes, such as reduced fission product decontamination factors, U/Pu co-processing and Pu/Np co-stripping, further improvements can be made addressing issues such as proliferation resistance and minor actinide burning, without adverse effects on the products. The cost-effective development of such flowsheets benefits from an understanding of the underlying process chemistry coupled with powerful modelling and simulation techniques. These can then be combined with a limited number of miniature scale solvent extraction trials to develop, optimise and ultimately define flowsheet envelopes for larger scale and/or fully active testing, if required. This paper reports recent progress made in the development of flowsheets for the co-stripping of Pu and Np from U in so-called advanced Purex processes using centrifugal contactors. In particular, the use of simple hydroxamic acids to strip both Pu and Np using complexation and reduction is considered with reference to solvent extraction trials in a miniature centrifugal contactor rig. These data are suitable for evaluation using process models with identification of significant parameters including distribution data, mass transfer rates and chemical kinetics. (authors)