Determination of the secondary phases at the acidic LNW disposal
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Determination of the secondary phases at the acidic LNW disposal Irina Vlasova1, Anna Romanchuk 1, Anna Volkova 2, Elena Zakharova 2, Igor Presnyakov1, Alexey Sobolev 2, Stepan Kalmykov 1 1 Department of Chemistry,Lomonosov Moscow State University, Moscow, Russia 2 Frumkin Institute of Physical chemistry and Electrochemistry RAS, Moscow, Russia ABSTRACT The migration behavior of the long-lived actinides was studied under the conditions of the deep disposal of the acidic liquid nuclear waste (LNW). Composition of LNW varies significantly including acidic technological wastes (pH a2.4), which consist of sodium nitrate, acetic acid, corrosion products (Fe, Cr, Mn, Ni, Al), fission products and actinides. Corrosion products tend to precipitate under the LNW disposal conditions that favor forming of the phases with high sorption capacity towards actinides. Sands of reservoir bed have their own initial sorbent surfaces besides new secondary phases that have formed as a result of interaction with acidic LNW. The nearest to the injection well conditions are gradually changing from pH a2.4 till neutral values due to the dilution by groundwater with formation of new precipitated phases of corrosion products. The solid phases characterization is a necessary step on the path of knowledge of migration behavior of actinides. The secondary phases of both corrosion products and sands of reservoir bed under LNW disposal conditions were characterized using XRD, SEM and Mössbauer spectroscopy. The recent results of the analyses of the behavior of actinides (Pu. U, Np, Am) under the conditions of the injection of the acid LNW are presented in the paper. INTRODUCTION The management of liquid nuclear wastes (LNW) in Russia includes the direct disposal of LNW into the deep geological formations [1-3]. At Tomsk site LNW have been injected into sandy rocks aquifers to the depth 290-380 m. The simulation of the radionuclides spreading in the operating strata requires the multi-scale study of the filtration / permeability properties of the rocks [4, 5] and speciation of radionuclides along with sorption capacity of the reservoir bed. Disposal conditions depend on the composition of LNW. The most challenging is the study of the behavior of technological acidic LNW with low pH values (pH 2.5), high salt content (140 g/L of NaNO3), presence of corrosion products (Fe3+; Cr3+; Al3+; Mn2+; Ni2+) and elevated temperature values. In the near-field conditions of the injection well the local temperature reaches the value of up to 150°С due to the accumulation of heat-producing short-lived radionuclides [6, 7]. Previously the influence of solid phases that were formed from corrosion products under hydrothermal conditions during the injection of acidic LNW on the migration behavior of Pu have been demonstrated [8, 9]. The present work is focused on the study of Pu, Am, Np and U migration behavior under the conditions of the reservoir bed as well as the identification and characterisation of the secondary phases that were precipitated during the interacti
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