Thermochromatographic oxidation studies of plutonium dioxide

The volatility of plutonium oxides in the O₂-H₂O_(g)/SiO_2(s) system has been studied by thermochromatography in the temperature range 1475 to 600 K. Oxides of uranium and neptunium have been studied for comparison. Oxide samples containing 10¹⁵ - 10¹⁶ actinide atoms were heated in the starting position of the thermochromatographic silica columns. Mixtures of helium, oxygen and water vapor were applied as reactive mobile gas phase. Resulting from thermochromatography the volatile actinide species are deposited in the column downstream, thus creating inner chromatograms along a temperature gradient. At the end of each experiment the actinide chromatograms were measured by alpha spectrometry.
Plutonium was found to be volatile in humid oxygen at temperatures above 1250 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 further evidence that water can oxidize plutonium dioxide.