Electrochemical mechanism of uranium mononitride dissolution in aqueous solutions of nitric acid

摘要

It was shown that the dissolution of UN with metallic conduction follows an electrochemical mechanism when it proceeds in contact with an electrically conductive medium (HNO3 solution). According to this mechanism, the oxidation of UN (at the anode) passes an electron into the UN matrix, which is a conductor, and can then reduce nitric acid in a parallel reaction a short distance away at another exposed surface of the UN (at the cathode). As a result, the reduction of HNO3 affords NO and NO2, while oxidation of uranium mononitride affords NH3, N-2, and N2O. The occurrence of these two separate processes accounts for the composition and yields of the products formed from UN and HNO3 as well as for the nitrogen isotope distribution between them when UN and HNO3 were labeled with N-14 or N-15. A mathematical equation describing the dependence of N-2 and N2O yields on HNO3 concentration was derived. It was also shown that the calculated value of standard electromotive force of the galvanic pair formed on the UN surface during its dissolution in HNO3 is high enough to initiate and support the electrochemical mechanism of its dissolution in nitric acid.