Reactivity of uranium in geopolymers, confinement matrices proposed to encapsulate MgZr waste

JOURNAL OF NUCLEAR MATERIALS

卷:518

Article

Cannes, C.¹  Rodrigues, D.¹  Barre, N.¹  Lambertin, D.²  Delpech, S.¹ 

[1] Univ Paris Sud 11, CNRS, Inst Phys Nucl, F-91406 Orsay, France

[2] Univ Montpellier, CEA, DEN, DE2D,SEAD, Bagnols Sur Ceze, France

关键词: Uranium;    Corrosion;    Geopolymer;    Fluoride ions;    Electrochemical measurements;   

DOI  :  10.1016/j.jnucmat.2019.03.024

来源: Elsevier

【 摘 要 】

The U reactivity has been examined in three geopolymer (GP) formulations: GP, GP containing 1.25 M of NaF (GP-NaF) and GP containing 1.25 M of NaF and a double concentration of NaOH (GP-NaF-NaOH). In a previous study, two mechanisms representative of uranium oxidation in basic aqueous solutions have been proposed, depending on the ratio of the fluoride and hydroxide ions concentrations (R-F/OH). For R-F/OH < 1, U is protected by the oxides layer UO2+x (mechanism A), while for R-F/OH > 1, U is continuously corroded (mechanism B). We have exploited the results on the GP pH evolution to understand the uranium behavior in geopolymers. With NaF at the saturated concentration in the geopolymers, if pH > 13.8, R-F/OH is lower than 1, while for pH < 13.8, this ratio is higher than 1. Moreover, the pH would be stabilized at 13.4 for GP and GP-NaF and 14.1 for GP-NaF-NaOH. The ratio Ropy can thus reach values higher than 1 in GP-NaF but not in GP-NaF-NaOH. Consequently, mechanism A can be applied for the U behavior in GP and GP-NaF-NaOH and mechanism B can occur in GP-NaF because of the pH decrease. The open circuit potential measurements confirm that in GP and GP-NaF-NaOH, U is protected by the oxides layer UO2+x while in GP-NaF, corrosion is observed after 10 days. In GP and GP-NaF-NaOH, the presence of the redox couple UO2+x/UO2 has been put in evidence by electrochemical impedance spectroscopy. This technique confirms a different behavior of uranium in GP-NaF. In the presence of fluoride ions, cracks in the GP have been observed and a great quantity of uranium oxide has been produced. (C) 2019 Elsevier B.V. All rights reserved.

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