SOLUBILITY OF SELECTED LANTHANIDE OXIDES USED AS NEUTRON POISONS:DYSPROSIUM OXIDE, HOLMIUM OXIDE AND GADOLINIUM OXIDE

摘要

The solubility of three lanthanide oxides, dysprosium oxide (Dy Dy2O3), holmium oxidern(Horn), Ho2O3) and gadolinium oxide (Gd ) Gd2O3) in aqueous solutions was investigated as a function ofrnpH, temperature and time. Solid oxide powders were equilibrated in aqueous solutions of knownrninitial pH for various times at controlled temperatures. The experiments were carried out withrnsolutions of pH values varying from 3 to 12 at temperatures between 20rn) ○C and 80 ○C for timernperiods from ~3 h to ~500 h. At the end of an experiment, the concentrations of the lanthanidernoxides in solution were determined using Inductively Coupled Plasma-Mass Spectrometry (ICPMS)rnor Inductively Coupled Plasma-Atomic Emissions Spectrometer (ICP-AES). There wasrninverse exponential dependence between the metal ion concentration and pH for the pH range 3rnto 10.3. All three oxides are very soluble in acidic solutions but have very low solubility inrnwater at pH 10.3, the approximate pH of the coolant in CANDUrn? reactors. There was nornmeasurable difference in the solubility of these metal oxides for solutions of pH 10.3 and 12.0.rnThe exposure time and temperature, for the time periods and the temperatures used in this work,rnhad a minimal effect on the concentrations of the dissolved oxides.