Coprecipitation Experiments Using Simulated Spent Fuel Solutions in the Presence of Metallic Iron in Synthetic Bentonitic-Granitic Water Under Oxidising Conditions

Abstract

This paper presents the results obtained from coprecipitation experiments of uranyl solutions in the presence of metallic iron and/or its alteration phases in synthetic bentonitic-granitic composition water. Experiments were done under oxidising conditions at room temperature. The pH range covered was 7.4 -8.8. Changes in the uranium concentrations and the characterisation of the secondary phases formed in the experiments were done using XRD and SEM-EDS and are presented herein.Final uranium concentration values were in the range of 2·10 -5 -5·10 -4 mol (kg of H 2 O) -1 . In all cases, results from these experiments did not show evidence of a clear effect due to the presence of iron (metallic or previously corroded) on the uranium concentration. These data were similar to those obtained by coprecipitation in similar conditions but in absence of iron material.Boltwoodite was observed [K 2 (UO 2 ) 2 (SiO 3 ) 2 (OH) 2 ·3H 2 O] in iron surface materials and characterized in all experiments. Based on the experimental data obtained (uranium concentration in solution and bulk solid phase characterisation) we propose the following surface-mediated reaction: 2

Microstructural Characterization of U Coprecipitated Phases Formed in Bentonic-Granitic Groundwater and under Anoxic Conditions

“…The TEM studies pointed out that the Fe particles (darker ones in Figures 12 and 13) were surrounded by precipitated secondary phases (calcium sodium uranate). The comparison of this results to those data obtained previously for some of the authors [5,6] under oxidizing conditions, indicates that the canister material plays a similar role with independence of the redox conditions considered (oxic or reducing conditions). Figure 14 shows the chemical analyses of this phase by EDX.…”

“…Against facts observed under oxidant conditions, where boltwoodite is the secondary phase observed [5], characterization by X-ray diffraction ( Figure 2) showed a low crystallinity solid mainly composed of schoepite and sodium uranate. Low crystallinity is due to a non-pure system, i.e., to the groundwater, a chemical composition of Sr, Ba, Mo, Y, La, Nd, Ru, Rd, Pd, and U, must be added.…”

“…In order to answer these questions, several cop-recipitation studies in different environments are being developed in CIEMAT [4][5][6]. These will allow us to establish which one is the secondary phase that will control the U solubility, if co-precipitation exists, etc.…”