New insight on the simultaneous H2 and HNO2 production in concentrated HNO3 aqueous solutions under alpha radiation

Knowledge of hydrogen and nitrous acid yields (G(H-2) and G(HNO2)) from alpha radiolysis of nitric acid solutions is of critical importance for the technological aspects of reprocessing of spent nuclear fuel (SNF). This study provides critical information on the G values for external alpha irradiation of concentrated HNO3 solutions. An investigation-specifically developed experimental setup allows performing this investigation without encountering issues related to extreme high local doses. In situ monitoring of the UV-visible induced absorption in irradiated HNO3 solutions permitted quantification of HNO2 production, and mass spectrometry was used to quantify H-2. The influence of the dose rate and HNO3 concentration was investigated, and the primary yields of these two species were determined. It was found that dose rate increase leads to diminished production of HNO2 and H-2, while HNO3 concentration increase leads to increased HNO2 formation and reduced H-2 production. The values of the primary yields of these two species were determined and compared to the literature reported values. While the determined values show similar trends as those reported, this study provides accurate radiolytic yields for H-2 and HNO2 that are radioelement-independent compared to the alpha radiolysis using radioisotope/HNO3 mixtures and provides the basis for perfecting numerical codes used for simulating the radiolytic processes associated with SNF reprocessing.