The Effect of Hydrogen Peroxide Concentration on the Oxidative Dissolution of Unirradiated Uranium Dioxide
- PDF / 159,777 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 26 Downloads / 291 Views
The Effect of Hydrogen Peroxide Concentration on the Oxidative Dissolution of Unirradiated Uranium Dioxide J. De Pablo, I. Casas, F. Clarens, F. El Aamrani and M. Rovira Chemical Engineering Department, Universitat Politècnica de Catalunya, 08028 Barcelona. Spain ABSTRACT The dissolution rate of unirradiated uranium dioxide was studied in batch experiments as a function of hydrogen peroxide concentration (from 10-5 to 10-3 mol dm-3). Unirradiated UO2(s) was used in order to differentiate surface chemical processes from radiolytic effects. Dissolution rates were determined from both uranium release and hydrogen peroxide consumption. Results showed that H2O2 consumption rate was higher than UO2 dissolution rate. This observation may indicate that the overall UO2 oxidative dissolution process would be controlled by the dissolution of the oxidized solid surface. The calculated hydrogen peroxide reaction order was 1 in the H2O2 concentration range from 10-5 to 10-4 mol dm-3, while at higher concentrations no clear dependence was observed. INTRODUCTION The effect of oxidant concentration on spent fuel matrix alteration is of a great importance in performance assessment studies for its final disposal in geological repositories. In the European repository concept, reducing conditions will prevail in the near field. However, oxidizing conditions are expected on the fuel surface due to water radiolysis. The main radiogenic oxidants identified as molecular species in spent fuel dissolution experiments are oxygen and hydrogen peroxide [1,2], while radicals have been postulated due to the characteristics of the radiolytic processes. The effect of oxygen on the matrix corrosion has been studied in detail by different authors [3,4,5,6] for both unirradiated UO2(s) and spent nuclear fuel. From these results, an oxidative dissolution mechanism has been recently proposed [7], which allows to explain spent fuel dissolution rates in carbonate medium at different oxygen partial pressures. However, when the oxygen partial pressure is low (0.003 atm) the spent fuel dissolution rates predicted by the mechanism are lower than the measured ones. This observation most likely indicates that other oxidants produced by radiolysis enhance the spent fuel dissolution. In this context, hydrogen peroxide can be one of the responsible of this enhancement. The information about the effect of the hydrogen peroxide on the UO2(s) dissolution is scarce [6,8,9,10]. In these works, the H2O2 concentrations used are usually much higher than those expected in the surface of spent nuclear fuel due to radiolysis. Dissolution rates were determined by corrosion potential measurements [6] or by the determination of the uranium concentration in solution [8,9]. No data of the hydrogen peroxide consumption during dissolution experiments are available in the literature. In this work, we have studied the dissolution rate of unirradiated uranium dioxide as a function of hydrogen peroxide concentration (from 10-5 to 10-3 mol dm-3) at constant pH=6. The
effect of carbonat
Data Loading...
