Incorporation of iodine into uranophane formed during the corrosion of spent nuclear fuel

Abstract

In order to evaluate the potential incorporation of 129 I into uranyl phases that would form during oxidative alteration of spent nuclear fuel, uranophane was synthesized under mild hydothermal conditions of 165 • C in the presence of iodide, iodate and periodate, respectively. The precipitates were examined and analyzed using powder X-ray diffraction (XRD), infrared spectroscopy (IR) and scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectroscopy (EDS). The results indicate that significant amount iodine can be incorporated into the structure of uranophane in the form of IO 4 − , and less in the form of IO 3 − . Crystallo-chemical analyses suggest that the incorporation mechanisms would be the substitution of iodate and periodate for SiO 4 tetrahedron in the sheet.

Mild Periodic Acid Flux and Hydrothermal Methods for the Synthesis of Crystalline f-Element-Bearing Iodate Compounds

“…Iodine-129 is one of the fission products in nuclear wastes, with a long half-life of 1.7 × 10 7 years. It was found that the initial formation of actinide iodate complexes or the incorporation of iodate anions in actinide-bearing minerals may occur after the accidental release of actinides and fission products. Therefore, the structures, thermostability, and spectroscopic properties of actinide iodates have been extensively explored during the past 2 decades. , Among these, rare coordination features were observed in both actinide- and iodine-based compounds, such as the hexaoxoiodate­(VII), cation–cation interactions between neptunyl units, where the axial oxygen of the actinyl unit further binds to another metal cation and acts as a bridging oxo atom, and tetraoxoiodate­(V) .…”

“…It was found that the initial formation of actinide iodate complexes or the incorporation of iodate anions in actinide-bearing minerals may occur after the accidental release of actinides and fission products. Therefore, the structures, thermostability, and spectroscopic properties of actinide iodates have been extensively explored during the past 2 decades. , Among these, rare coordination features were observed in both actinide- and iodine-based compounds, such as the hexaoxoiodate­(VII), cation–cation interactions between neptunyl units, where the axial oxygen of the actinyl unit further binds to another metal cation and acts as a bridging oxo atom, and tetraoxoiodate­(V) . A series of functional materials with potential applications such as nonlinear-optical (NLO) materials (primarily due to stereochemically active lone-pair electrons in the iodate unit), selective ion-exchange properties, and intercalation of the neutral molecules of HIO 3 or KCl have also been prepared. ,, Furthermore, structural deviation was shown in the hexavalent uranium, neptunium, ,,, and plutonium − series and the trivalent americium, curium, , and californium series, which originates from the discontinuity in their chemical properties entailing solubilities, redox potentials, electron orbital involvement, etc.…”

Incorporation of iodate into uranyl borates and its implication for the immobilization of 129I in nuclear waste repositories

“…In the reported iodate substitution, both the SiO 4 and PO 4 polyhedra are isolated with other SiO 4 or PO 4 polyhedra [27][28][29]. In contrast, the BO 3 or BO 4 polyhedra in KUB and NaUB structure are connected to other BO 3 or BO 4 polyhedra to form framework.…”

“…The trace amount of iodine in KUB samples may be contributed by iodine inclusion, or intercalated between the layers. Generally, anions with similar valences and geometries can easily substitute for one another, such as ( [27,28]. However, the length of I-O bond ranges between 1.77 Å and 1.86 Å and is much longer than the B-O bond (1.36-1.49 Å).…”

“…Owing to its long half-life and bioavailability, 129 I is a radionuclide of special concern in repositories. Our previous studies have shown that 129 I can be incorporated into a uranyl silicate and three uranyl phosphate in the form of iodate [27,28]. Recently, we reported the coupled substitution of Np 5+ and iodate into a uranyl phosphate [29].…”