Sorption of radionuclides on the rocks of the exocontact zone of Nizhnekansky granitoid massif
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Sorption of radionuclides on the rocks of the exocontact zone of Nizhnekansky granitoid massif Irina Vlasova 1, Vladimir Petrov 1, Natalia Kuzmenkova 1, Artem Kashtanov 1, Vladislav Petrov 2, Valery Poluektov 2, Stepan Kalmykov 1,3, Jörg Hammer 4 1 Department of Chemistry, Lomonosov MSU, Moscow, Russia 2 Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry of RAS, Moscow, Russia 3 National Research Center “Kurchatov Institute”, Moscow, Russia 4 BGR, Geozentrum Hannover, Hannover, Germany ABSTRACT Study of sorption behavior of radionuclides toward five rock samples drilled in the deepwell R12 in the exocontact zone of Nizhnekansky granitoid massif (“Eniseysky” area) in the range of depth 166 m – 476 m was carried out. The sorption kinetics and Kd values of the longlived radionuclides of different chemical behavior 137Cs, 226Ra, 79Se, 237+239Np, 239,240Pu, 241,243 Am were determined. Experiments were performed under the conditions that are relevant for the future high level waste disposal (atmosphere; composition, pH and Eh of the solutions). Digital radiography demonstrated heterogeneous sorption of all the investigated radionuclides and revealed phases with higher sorption ability. It was established that sorption of metal cations is fast and reaches steady state in a few hours while Se in the form of selenate-ion sorbs insignificantly. INTRODUCTION The principal concept of the high level wastes (HLW) disposal into the deep crystalline rock formations is accepted in Russia [1]. Several perspective sites of Nizhnekansky granitoid massif (Itatsky, Kamenny areas) have been thoroughly studied [2-4]. Recently Eniseysky area is chosen as a site of an underground research laboratory for final isolation of HLW and some geological and geophysical researches have been performed in the area. In 2016 the building of Underground Research Lab (URL) at the Eniseysky area will begin. According to Safety standards of IAEA and the idea of multibarrier systems the crystalline rocks are the last barrier to prevent radionuclides release from the repository to the environment [5]. The backfilling of the canisters with the vitrified HLW by bentonites (Khakassiya) is accepted in Russia. Thus, determination of sorption properties of the host rocks in the presence of the simulated ground water, pre-equilibrated with bentonites, towards long-lived radionuclide is essential for safety assessment of future HLW repository. Time dependence of sorption of cesium (I), plutonium (IV), americium (III) and neptunium (V) onto samples of leucogranite, tonalite and granodiorite from Nizhnekansky massive (Itatsky and Kamenny areas) was studied earlier [3, 4]. The distribution coefficients for Cs, Pu and Am were found to be n·102 - n·103 mL/g and only up to 2 mL/g for Np. These previous studies were performed in aerobic conditions that are not relevant for the deep geological media with low oxygen content. The presence of oxygen and other redox active substances (Fe2+, H2, O22- etc.) is controlling the Eh values of the aqueous sol
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