Radiation induced dissolution of (U, Gd)O2 pellets in aqueous solution – A comparison to standard UO2 pellets

The behavior of spent nuclear fuel exposed to groundwater is crucial in the safety assessment of a deep geological repository for spent nuclear fuel. For this reason, leaching experiments on spent nuclear fuel as well as non-radioactive analogues have been conducted for several decades. Although the processes involved can be considered to be fairly well understood, there is a need for further experimental studies whenever new fuel types are introduced. Fuels with burnable absorbers are now in use but very little is known about their behavior under repository conditions. In this work, the impact of burnable absorbers doping (Gd, 3–8%wt.) on the oxidative dissolution of UO ₂ in an aqueous system was studied in H ₂O ₂ and γ-irradiation induced dissolution experiments. The results showed a significant decrease in uranium dissolution and lower reactivity towards H ₂O ₂ for (U,Gd)O ₂ pellets compared to standard UO ₂. The resulting decrease in the final oxidative dissolution yield was mainly attributed to decreased redox reactivity of the UO ₂ -matrix upon doping. The results of the gamma radiation exposures display an even larger effect of Gd-doping. These findings indicate that other processes are involved in the radiation-induced dissolution of Gd-doped UO ₂ compared to pure UO ₂.