The subject of this postoctoral position is related to the optimization of the process used to separate uranium and plutonium from spent nuclear fuels. In the so called PUREX process currently in operation at La Hague reprocessing plant in France, the TBP (tri-n-butylphosphate) is used as extractant in the solvent extraction system. This molecule shows high affinity for uranium and plutonium at oxidation states VI and IV and allows to reach high decontamination factors versus fission products. Nevertheless, the separation of U from Pu requires the use of reducing and anti-nitrous reagents to allow the back-extraction of Pu(III). In order to improve the process, researches are under way to design new extractant molecules which would allow to separate U and Pu without redox chemistry and with high selectivity versus fission products (Ru, Tc, Cs, lanthanides, etc) and other actinides (especially Np). The objective of the postdoctoral associate will be to select the molecules, to determine synthesis routes and to perform their synthesis using equipment available in the LCPE laboratory (micro-wave, flash chromatography, NMR, HPLC-MS, GC-HRMS) at the CEA Marcoule.