Oxidative dissolution of Cr-doped UO 2 nuclear fuel.

Alternative UO 2 nuclear fuels, incorporating Cr as a dopant, are currently in use in light-water reactors. Dissolution experiments using Cr-doped UO 2 , performed as a function of Cr content in a simplified groundwater solution and under oxic conditions, established that the addition of Cr to the UO 2 matrix systematically reduced the normalised dissolution rate of U at 25 and 40 °C. This effect was most notable under dilute solution conditions, and is the result of galvanic coupling between Cr and U, resulting from the presence of Cr 2+ in the UO 2 matrix, as corroborated by activation energy determination. Under conditions of solution saturation, where schoepite ((UO 2 ) 8 O 2 (OH) 12 ·(H 2 O) 12 ) and Na 2 U 2 O 7 ·6H 2 O were identified as secondary phases, the rate of U dissolution was invariant with Cr content. Moreover, at 60 °C, the trend was reversed and the rate of U dissolution increased with increasing Cr content. Under these conditions, other factors, including U solubility or bicarbonate-surface interactions, exert a stronger influence on the U dissolution kinetics than Cr. Increased grain size, a feature of Cr-doped UO 2 fuel, was also found to reduce the normalised dissolution rate of U. In establishing the mechanisms by which Cr dopants influence UO 2 fuel dissolution, it can be concluded that, overall, Cr-doped UO 2 nuclear fuel possesses similar dissolution kinetics to undoped UO 2 fuel, giving confidence for its eventual disposal in a geological facility.