Understanding the solid/liquid interface evolution during the dissolution of Nd-doped UO2 by macro-/microscopic dual approach

Abstract

The chemical durability of Nd-doped UO2 samples was studied using an innovative macro-/microscopic dual approach method. The starting precursor was first prepared by a hydroxide co-precipitation route leading to a nano-sized powder associated to high specific surface area. The powder was then converted into U0.8Nd0.2O2±y solid solution by calcination. After shaping of the oxide powder into the pellet form through uniaxial pressing at 500 MPa, the pellets were sintered at 1600 °C under inert (Ar) or reducing (Ar-4%H2) atmosphere. At the macroscopic scale, multiparametric dissolution tests were carried out under static conditions in 2 mol.L−1 HNO3 at 60 °C. Simultaneously, an operando monitoring of the solid/liquid interface evolution during dissolution was also performed by ESEM at the microscopic scale, in order to follow the consequences of the dissolution on the ceramics microstructure. This dual approach was validated by comparing the calculated normalized dissolution rates obtained for each series of experiments. Changing the sintering atmosphere did not appear to significantly affect the dissolution kinetics of Nd-doped UO2 samples at the macroscopic scale whereas notorious differences in the dissolution mechanisms have been highlighted at the microscopic scale by ESEM monitoring solid/liquid interface.