The β-emitting 99Tc isotope is a high-yield fission product in 235U and 239Pu nuclear reactors, raising special concern in nuclear waste management due to its long half-life and the high mobility of pertechnetate (TcO4−). Under the conditions of deep nuclear waste repositories, Tc is retained through biotic and abiotic reduction of TcO4− to compounds like amorphous TcO2 ⋅ xH2O precipitates. It is generally accepted that these precipitates have linear (Tc(μ-O)2(H2O)2)n chains, with trans H2O. Although corresponding Tc−Tc and Tc−O distances have been obtained from extended X-ray absorption fine structure (EXAFS) spectroscopy, this structure is largely based on analogy with other compounds. Here, we combine density-functional theory with EXAFS measurements of fresh and aged samples to show that, instead, TcO2 ⋅ xH2O forms zigzag chains that undergo a slow aging process whereby they combine to form longer chains and, later, a tridimensional structure that might lead to a new TcO2 polymorph.
Bibliographical noteFunding Information:
The research was funded by the European Commission (EC) through the EURAD FUTURE T3 project (H2020‐847593) and by the German Federal Ministry of Education and Research (BMBF) through the KRIMI project (02NUK056C). The authors also thank Prof. Bernd Grambow (SUBATECH Nantes, France) for fruitful discussions. Open Access funding enabled and organized by Projekt DEAL.
© 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.
All Science Journal Classification (ASJC) codes
- Organic Chemistry