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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 H2O2 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 H2O2 resulted in matrix dissolution. However, this oxidative dissolution induced by H2O2 is more prominent than hydrolysis in water with or without added HCO3−. The dissolution of UN was compared with other nuclear fuel materials (UC, UO2 and U3Si2) under the same conditions. The results show that UN is the second most reactive fuel material towards H2O2. However, the so-called dissolution yield is the lowest for UN. The rationale for the observed differences in reactivity are discussed., QC 20230704

Uranium carbide (UC) is a candidate fuel material for future Generation IV nuclear reactors. As part of a general safety assessment, it is important to understand how fuel materials behave in aqueous systems in the event of accidents or upon complete barrier failure in a geological repository for spent nuclear fuel. As irradiated nuclear fuel is radioactive, it is important to consider radiolysis of water as a process where strongly oxidizing species can be produced. These species may display high reactivity toward the fuel itself and thereby influence its integrity. The most important radiolytic oxidant under repository conditions has been shown to be H2O2. In this work, we have studied the dissolution of uranium upon exposure of UC powder to aqueous solutions containing HCO3- and H2O2, separately and in combination. The experiments show that UC dissolves quite readily in aqueous solution containing 10 mM HCO3- and that the presence of H2O2 increases the dissolution further. UC also dissolves in pure water after the addition of H2O2, but more slowly than in solutions containing both HCO3- and H2O2. The experimental results are discussed in view of possible mechanisms., QC 20211117

QC 20221129

QC 20221129

QC 20221129

QC 20230906