Technetium (99Tc) is among the most problematic fission products in nuclear waste due to its high fission yield (6%), long half life (0.21 Ma), and the environmental mobility of pertechnetate, TcO4-, the most stable form of technetium in aerobic environments. Technetium can also create problems during processing of spent nuclear fuel and during vitrification of nuclear waste. In particular, Tc(VII) species can evaporate from the glass melt unless the electrochemical potential is sufficiently reducing. Alternatives to glass include waste forms based on environmentally stable natural analogs such as Synroc (titanate ceramic) or TiO2 itself. The incorporation of Tc into TiO2 nanoparticles means of simple, aqueous chemistry is presented starting from TcO4- in 5 M nitric acid. A combination of X-ray diffraction, X-ray absorption fine structure spectroscopy, and UV-Visible spectroscopy reveals that pairs of Tc(IV) ions replace pairs of Ti(IV) ions in TiO2. Tc-doped TiO2 samples were suspended in deionized water under aerobic conditions, and the release rate of Tc under these conditions was determined. The results of this work show that Tc leaches too quickly from the TiO2 nanoparticles for them to be viable waste forms. Comparison with the leach rates of Tc-doped iron oxides strongly suggests that the leach rate of Tc from iron oxide and TiO2 nanoparticles is controlled by solid state diffusion.

Preparation of Tc-doped TiO2 by simple aqueous chemistry and leaching leaching behavior of Tc

2019 Spring National Meeting

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