title: Impeding (99)Tc(IV) mobility in novel waste forms.
abstract: Technetium ((99)Tc) is an abundant, long-lived radioactive fission product whose mobility in the subsurface is largely governed by its oxidation state. Tc immobilization is crucial for radioactive waste management and environmental remediation. Tc(IV) incorporation in spinels has been proposed as a novel method to increase Tc retention in glass waste forms during vitrification. However, experiments under high-temperature and oxic conditions show reoxidation of Tc(IV) to volatile pertechnetate, Tc(VII). Here we examine this problem with ab initio molecular dynamics simulations and propose that, at elevated temperatures, doping with first row transition metal can significantly enhance Tc retention in magnetite in the order Co>Zn>Ni. Experiments with doped spinels at 700 °C provide quantitative confirmation of the theoretical predictions in the same order. This work highlights the power of modern, state-of-the-art simulations to provide essential insights and generate theory-inspired design criteria of complex materials at elevated temperatures.
authors.affiliation: Fundamental and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352, USA.
authors.forename: Mal-Soon
authors.initials: MS
authors.lastname: Lee
authors.affiliation: Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352, USA.|Pohang University of Science and Technology, Pohang 37673, South Korea.
authors.forename: Wooyong
authors.initials: W
authors.lastname: Um
authors.affiliation: Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352, USA.
authors.forename: Guohui
authors.initials: G
authors.lastname: Wang
authors.affiliation: United States Department of Energy, Office of River Protection, Richland, Washington 99352, USA.
authors.forename: Albert A
authors.initials: AA
authors.lastname: Kruger
authors.affiliation: Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: Wayne W
authors.initials: WW
authors.lastname: Lukens
authors.affiliation: Fundamental and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352, USA.
authors.forename: Roger
authors.initials: R
authors.lastname: Rousseau
authors.affiliation: Fundamental and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352, USA.
authors.forename: Vassiliki-Alexandra
authors.initials: VA
authors.lastname: Glezakou