Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

Safety assessment studies for low- and intermediate level nuclear waste (L/ILW) repositories predict selenium-75 to be an important dose-determining radionuclide due to its long half-live and its presence in the anionic form resulting in weak retention by common near- and far field minerals. However, such predictions ignore the potential uptake by positively charged anion exchangers present in the cementitious near-field of a L/ILW repository, such as ettringite and hydrocalumite (AFm phases), a group of Ca, Al–layered double hydroxides.
The objective of this work is to investigate the immobilisation of Se under the alkaline and reducing conditions existing in a cement-based repository (-230mV < Eh < -750 mV, 10.0 < pH < 13.5). Under these conditions, Se(IV) and Se(-II) are the dominating redox states and the aqueous Se speciation is dominated by anionic species SeO32-, HSe2- and a series of polyselenides, mainly Se22-, Se32- and Se42-.