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.