Study of SIMFUEL corrosion under hyper-alkaline conditions in the presence of silicate and calcium
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Study of SIMFUEL corrosion under hyper-alkaline conditions in the presence of silicate and calcium Authors: Alexandra Espriu-Gascon1, David W. Shoesmith2, Javier Giménez1, Ignasi Casas1, Joan de Pablo1,3 Affiliations: 1Escola d’Enginyeria de Barcelona Est (EEBE), Carrer d’Eduard Maristrany, 10-14, 08019 Barcelona, Spain. 2 Department of Chemistry, The University of Western Ontario, 1151 Richmond Street, London, Ontario, Canada N6A 5B7 3 Fundació CTM Centre Tecnològic, Plaça de la Ciència 2, 08243 Manresa, Barcelona, Spain ABSTRACT Cement has been considered as a possible material present in the Deep Geological Disposal (DGD) [1] . In order to determine the effect of cementitious waters on the oxidation of the surface of Spent Fuel (SF), a series of electrochemical experiments were performed, to study the influence of two main components of cementitious water: calcium and silicate. Test solutions with Na2SiO3 and/or CaCl2 were prepared at pH 12 and NaCl 0.1 mol·dm-3 as ionic medium. A 3 at.% doped SIMFUEL was used to perform cyclic voltammetric (CV), potentiostatic and corrosion potential (ECORR) experiments. After potentiostatic and ECORR experiments, the SIMFUEL surface was analyzed using X-Ray Photoelecton Spectroscopy (XPS). The results showed that the presence of silicate decreased the SIMFUEL oxidation between -100 mV and 300 mV. When Ca2+ was added, the whole oxidation process was shifted to higher potentials which indicated a protective effect of the combination of Ca2+ and SiO32- . The XPS results obtained after potentiostatic experiments at 200 mV showed that the presence of silicate partially suppressed the oxidation of SIMFUEL, as indicated by the contribution of both U(IV) and U(V) XPS to the U 4f7/2 band (~ 38%). After the addition of calcium, the predominant uranium oxidized state contribution on the surface was U(V) (40%). After the ECORR experiments, the ECORR values were similar either with or without silicate in solution (-80 mV and -70 mV respectively). The resulting surface also exhibited a similar composition. When calcium was added to the electrolyte, the ECORR value was suppressed to -105 mV, and XPS showed that the surface was less oxidized than with the other two electrolytes. INTRODUCTION In the spent fuel near field many reactions between the water and the spent fuel (SF) can occur depending on the solution composition, redox conditions, and pH. Experimental studies with actual SF are expensive and complex. In order to assess the SF performance some studies have been carried out using SF analogues such as SIMFUEL [2]–[4]. Cement has been proposed for use in the deep geological disposal to seal possible cracks in the different structures. Waters in contact with cementitious materials have high pH values and contain silicate and calcium ions [5], [6]. However, SF corrosion under these conditions has not been extensively studied. Some studies on the influence of very alkaline pH values on UO2 dissolution have been published [7], [8]. Santos et al. [9] studied the influence of pH on the corros
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