PRODUCTION AND ADSORPTION OF VOLATILE TELLURIUM HEXAFLUORIDE

Research and development supporting the management of off-gases from nuclear fuel reprocessing has historically been focused on the off-gas streams that arise from aqueous reprocessing technology. With the advent of advanced reactor designs off-gas streams arising from advanced reprocessing methodology, such as that of FV [fluoride volatility] processing, also merit consideration. This work focuses on TeF₆ [tellurium hexafluoride], one of the most volatile radioactive compounds produced during FV, and investigates TeF₆ production, measurement, and abatement technologies.

To assist in on-line monitoring of TeF₆ by Fourier-transformed infrared spectroscopy, this work systematically used the ideal gas law and Beer’s Law to report a new molar absorptivity coefficient for TeF₆ at 752 cm^-1 of 28.51 ± 1.35 cm² Torr^-1.

TeF₆ was produced by the fluorination of Te metal across a temperature range of 100-250°C (degrees Celsius) with a fluorine pressure of 20 Torr. Reaction progress was very fast above 250°C. Two particle sizes of Te metal were used in testing and no significant change in reaction rate was observed for these different particle sizes under the experimental conditions used. When fluorine partial pressure was increased to 40 Torr, the reaction rate was too quick to be measured by this experimental system. It was observed that about 80% of the starting Te metal was converted and that this conversion rate was independent of reaction temperature.

Sorption of TeF₆ in the presence of F₂ [fluorine] by activated alumina was very fast and complete. No practical differences in TeF₆ sorption were observed across the two F₂ pressures used. TeF₆ was observed to be fully removed by copper when the sorbent was heated above 300°C and when fluorine was not present in the gas stream. Sorption was slow, requiring 50 minutes for full TeF₆ removal. SEM [scanning electron microscopy] of the discharged copper sorbent confirmed that Te was present on the copper surface.