On the Stability of Uranium Carbide in Aqueous Solution-Effects of HCO3 - and H2O2.

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.