Effect of temperature and bicarbonate concentration on the kinetics of UO_2(s) dissolution under oxidizing conditions

摘要

The dissolution rate of unirradiated UO_2 (s) has been studied as a function of hydrogen carbonate concentration at three different temperatures (298. 15 K, 313. 15 K and 333. 15 K) under oxidizing conditions in a continuous flow-through reactor with a thin layer of solid particles (article size from 100 to 300 um m). From the results of these experiments, two different rate laws have been determined. At high temperature (313. 15K and 333. 15K), we obtained a dissolution rate proportional to hydrogen carbonate concentration while at 298. 15K, the rate almost depends on the square root of the hydrogen carbonate concentration. This indicates a different reaction mechanism depending on temprature which can be related to the oxidation step of the overal process. The apparent activation energy obtained was 41 kJ mol~-1.