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• Stability of uranium mono-nitride under simulated geological repository conditions. • Oxidative dissolution of different uranium based materials in the presence of H 2 O 2 - the dominant aqueous radiolysis product. • Highest reactivity towards H 2 O 2 for UN and UO 2 among the different uranium based materials. • Lowest uranium dissolution concentrations for UN despite its high reactivity to H 2 O 2. Uranium nitride (UN) has good thermo-physical properties which makes it a promising fuel candidate for generation IV nuclear reactors. In addition to its performance as a nuclear fuel, it is important to elucidate every novel fuel material in terms of its stability in aqueous environments. This can be highly relevant under certain accident scenarios and also for the safety assessment of geological repositories for used nuclear fuel. The fuel matrix contains the fission products and heavier actinides formed under normal reactor operation. Upon dissolution of the fuel matrix, these highly radiotoxic constitiuents can be released. In this work UN has been studied under aqueous conditions similar to a geological repository for spent nuclear fuel. For UN, direct hydrolysis as well as oxidative dissolution induced by water radiolysis can lead to degradation of the fuel matrix. The latter process leads to formation of oxidative radiolysis products of which H 2 O 2 has been shown to be the most important oxidant for other fuel materials. The experiments show that hydrolysis of UN in aqueous solutions and exposure to solutions containing H 2 O 2 resulted in matrix dissolution. However, this oxidative dissolution induced by H 2 O 2 is more prominent than hydrolysis in water with or without added HCO 3 −. The dissolution of UN was compared with other nuclear fuel materials (UC, UO 2 and U 3 Si 2) under the same conditions. The results show that UN is the second most reactive fuel material towards H 2 O 2. However, the so-called dissolution yield is the lowest for UN. The rationale for the observed differences in reactivity are discussed. [ABSTRACT FROM AUTHOR]