Sorption of Np and Tc in Underground Waters by Uranium Oxides T.V.Kazakovskaya,a V.I. Shapovalova, N.V. Kushnira , E.V. Zakharovab, S.N.Kalmykovb O.N.Batukb, M.J.Hairec a –Russian Federal Nuclear center –All-Russia Scientific Institute of Experimental Physics; 607190, Sarov, Russia, E-mail:
[email protected]; b – Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Moscow, Russia, c – Oak Ridge National Laboratory, Oak Ridge, Tennessee. Abstract –The production of nuclear fuels results in the accumulation of large quantities of depleted uranium (DU) in the form of uranium hexafluoride (UF6), which is converted to uranium oxides. Depleted uranium dioxide (DUO2) can be used as a component of radiation shielding and as an absorbent for migrating radionuclides (especially 237Np and 99Tc). These may emerge from casks containing spent nuclear fuel (SNF) that are stored for hundreds of thousands of years in high-level wastes (HLW) and SNF repositories (e.g. Yucca Mountain Project). In this case DU oxides serve as an additional engi- neered chemical barrier. This work is a part of the joint Russian –American Program on Beneficial Use of Depleted Uranium. This paper describes the UO2 transformations that take place in contact with various aqueous media (deionized water (DW), J-13 solution that simulates Yucca Mountain ground water, etc.) and sorption of long-lived radionuclides (237Np and 99Тс) from these media by depleted uranium dioxide. Samples of depleted uranium dioxide used in this work originated from the treatment of UF6 in a reducing media to form UO2 (DUO2-1 at 600°C, DUO2-2 at 700°C, and DUO2-3 at 800°C).