A Study of Uranium(V) Species in Alkali Chloride Melts

Abstract

Reactions leading to the formation of uranyl(V) species in fused alkali chlorides were studied. The reactions investigated include thermal decomposition of uranyl(VI) chloride in alkali chloride melts, electrochemical and chemical reduction of UO 2 2+ ions in LiCl, 3LiCl-2KCl, NaCl-KCl and NaCl-2CsCl melts at 550-850 o C. Elemental tellurium, palladium, silver, molybdenum, niobium and zirconium were tested as the reducing agents. The outcome of the reaction depends on the electrochemical properties of the reductant.

The Effect of Fission Product Elements on the Behavior of Uranyl Species in Alkali Chloride Melts: a Contribution towards Reprocessing Spent Oxide Fuels

“…In the presence of molybdenum the noble fission product chloro complexes of ruthenium, rhodium and palladium are reduced to the metallic state, e.g., 3 PdCl 6 4-+ 2 Mo → 3 Pd + 2 MoCl 6 3-+ 6 Cl - [6] and deposited on molybdenum. Zirconium and niobium will be deposited on the uranium dioxide formed by reaction [2] according to the reactions [3][4][5].…”

“…The experimental techniques have been described previously (6,15). Electronic absorption spectra were measured using a custom built set-up comprising a fiber optic spectrometer, AvaSpec-2048-2 (Avantes), and an optical furnace, INSTRON SFL TF1726.…”

“…The usual routes to uranium(V) involve reducing U(VI) or oxidizing U(IV) species. Uranyl(V) ions are the intermediate species formed during the cathodic reduction of uranyl(VI) although in some early reports concerning electrodeposition of UO 2 from fused chlorides the possibility of uranyl(V) formation was overlooked (4)(5)(6)(7). The electrochemical and thermodynamic properties of uranyl(V) in individual alkali chlorides and their mixtures was studied in detail by .…”

“…The addition of carbon into a uranyl(VI)-containing chloride melt results in a twostep reduction to UO 2 (deposited on the carbon surface) via intermediate soluble uranyl(V) chloro-species (12). Hydrogen reduction of uranyl(VI)-containing chloride melts ultimately leads to the precipitation of UO 2 but a detailed spectroscopy study of the reaction showed that dioxo-and even monooxo-uranium(V) species are formed as the intermediates (13)(14)(15). Thermal decomposition of uranyl(VI) chloride in fused salts also yields uranyl(V) species (1,2,4,6,12).…”

“…Hydrogen reduction of uranyl(VI)-containing chloride melts ultimately leads to the precipitation of UO 2 but a detailed spectroscopy study of the reaction showed that dioxo-and even monooxo-uranium(V) species are formed as the intermediates (13)(14)(15). Thermal decomposition of uranyl(VI) chloride in fused salts also yields uranyl(V) species (1,2,4,6,12). Lowering the partial pressure of Cl 2 above the melt, e.g., by positioning a Zr getter in the atmosphere above the melt or sparging the melt with a suitable gas (argon or hydrogen chloride) sweeping Cl 2 , facilitates the decomposition process (12,15).…”