Volatized Tellurium Interactions with Organics and with Boric Acid

Licentiate thesis, 2024

Tellurium is a volatile fission product with a complex chemistry that must be accounted for in case of a nuclear accident. Specifically, its interactions with organic species and with boric acid, both which are expected in the accident chemistry, are largely unknown. This study aims to explore the interactions between tellurium aerosols and three organic species (acetone, propanol, and methane), and with boric acid at temperatures representing the primary circuit of a pressurized water reactor. Oxidizing (Air), inert (N2) and reducing (Ar/H2) atmospheres are all investigated. Analysis involves ICP-MS of liquid samples, XPS of solid filter samples, as well as online measurements, mainly to categorize the aerosols produced during the experiments, as well as FTIR. Furthermore, neutron activation and gamma spectroscopy are used.

The results indicate that tellurium may form small amounts of organic tellurides in these conditions, specifically under inert and reducing conditions. These results are not conclusive, as no analysis detected these species. However, data from both XPS and ICP-MS may imply their formation. In general though, the ICP-MS data imply low volatility of tellurium in these conditions, as the concentration in the liquid trap remains in the μM to nM range.

As for boric acid, no indication was found of direct interaction between boric acid and tellurium. However, XPS analysis does imply that the oxidation of the tellurium is reduced by the presence of boric acid. This was inferred mainly from XPS analysis and may potentially be an important consideration for future studies of tellurium in the context of severe nuclear accidents. Volatility remains at the low μM level, though formation of H2Te does serve to increase it. This only occurs at high temperature in reducing atmosphere, however.