Thermochromatographic Volatility Studies of Actinide Oxides

The volatility of plutonium oxides in the O2-H2O(g)/SiO2(s) system has been studied by thermo-chromatography in the temperature range 1475 to 600 K. Oxides of thorium, protactinium, uranium, neptunium, and americium in trace amounts have been studied for comparison. Oxide samples containing 105 – 1016 actinide atoms were heated in the starting position of the ther-mochromatographic silica columns. Mixtures of helium, oxygen and water vapor were applied as reactive mobile gas phase. Resulting from thermochromatography the volatile actinide spe-cies are deposited in the column downstream, thus creating inner chromatograms along a temperature gradient. At the end of each experiment the actinide chromatograms were meas-ured by alpha spectrometry. Gamma spectrometry was used to measure protactinium.
Plutonium was found to be volatile in humid oxygen at temperatures above 1300 K. The Pu volatility is lower than that of uranium, but higher as one would expect for stable Pu(IV) which is nonvolatile under the applied experimental conditions. The Pu volatility is assigned to PuO2(OH)2(g). The experimental results give evidence of the oxidation of PuO2 and NpO2 to higher oxides by moist oxygen.