[en] In the present work, we have addressed an important redox reaction, the reduction of U(VI) to U(V) in the presence of Fe(II). Redox reactions are not only of fundamental interest, to understand them is essential when describing how chemical reactions of actinides in surface and groundwater systems affect their mobility in the biosphere, and the function of engineered systems for the containment of radioactive waste in underground repositories. In this context it is important to notice that spent nuclear fuel is predominantly a matrix of UO₂ in which fission products and higher actinides are dispersed. In contact with water the fuel matrix will dissolve with a resulting release of the different radionuclides; the dissolution is a result of oxidation by radiolysis products or by intruding oxygen. In most technical system the nuclear waste is contained in canisters of iron/steel, which provide a large reduction capacity to the system and thus may prevent the transformation of sparingly soluble UO₂ to more soluble U(VI) species. Corrosion and other redox reactions involving iron species are therefore of key importance for the safe performance of many nuclear waste installations; as these have to function over very long time periods it is highly desirable to base predictions of their future environmental effects on molecular understanding of the chemical reactions taking place