Activities related to nuclear energy always involve processes ranging from mining extraction to fuel reprocessing, as well as waste storage, involving ionizing radiation. We have focused our efforts on studying the reactions that occur during nuclear fuel processing, with the aim of improving this process, which allows for saving uranium. The solvent studied is a mixture of water and TriButylPhosphate [Wang2018], as illustrated in Figure 1. After investigating the solvation of the electron in this mixture [Bahry2021], we studied the radiolysis of solutions used in the reprocessing of spent fuel, which are highly concentrated in nitric acid. Nitric acid (HNO3) plays a central role in nuclear technology, particularly in the separation and extraction processes of actinides. In this study, three mechanisms contributing to the formation of nitrate radicals (NO3•) in concentrated nitric acid were explored by measuring the radiolytic yield of NO3• at ambient and elevated temperatures [Musat2018,Musat2020a]. We also conducted pulsed radiolysis measurements to determine the rate constant of the reaction between NO3• radicals and U(IV). The decay of the NO3• radical was monitored, and its reaction rates with hydrazinium nitrate, ammonium hydroxyl nitrate, and U(IV) were measured at ambient temperature and at 45°C, under conditions similar to those of spent fuel reprocessing.