Thermodynamic analysis of uranium oxides fluorination with HF(g) and F 2 (g)
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Thermodynamic analysis of uranium oxides fluorination with HF(g) and F2(g) Federico J. Pomiro1 · Juan P. Gaviría1,2 · Ana E. Bohé1,2,3 · Georgina De Micco1,2 Received: 9 February 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract This paper presents a thermodynamic analysis of the fluorination of U O2(s) and U O3(s) with HF(g) and F 2(g). The reaction mechanisms, intermediates and final products were analyzed using different thermodynamic calculations, including free energy change, phase stability and equilibrium composition diagrams. In the U–O–F system uranium oxyfluorides are necessarily formed between uranium oxides and fluorides. The effect of low pressure gaseous products was analyzed. The F4(s) is thermodynamically feasible at temperatures higher than 680, reaction between UO2F2(s) and HF(g) to produce U 320 and 160 °C for pO2(g) 10−3, 10−4 and 1 0−5 atm, respectively. This appears to be a potential yield loss mechanism during the fluorination in flow reactors. Keywords Fluorination · Uranium oxide · Uranium oxyfluoride · Thermodynamic · Hydrogen fluoride · Fluorine
Introduction The reaction of uranium oxides with F 2(g) and HF(g) was studied in the 1960s for the production of uranium hexafluoride (UF6), required by the nuclear industry [1], and for reprocessing spent nuclear fuels [2]. Several methods have been reported for preparing UF6 from uranium oxides with different fluorination agents such as cobaltic fluoride, fluorine at atmospheric and high pressure, liquid bromine trifluoride [3] and nitrogen trifluoride [4]. Anastasia et al. studied a two-step process of oxidation and fluorination reactions to obtain UF6 from UO2(s) pellets from spent Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10967-020-07166-w) contains supplementary material, which is available to authorized users. * Georgina De Micco [email protected] 1
Departamento de Fisicoquímica y Control de Calidad, Complejo Tecnológico Pilcaniyeu, Centro Atómico Bariloche, Comisión Nacional de Energía Atómica, Av. Bustillo 9500, 8400 S.C. de Bariloche, Río Negro, Argentina
2
Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), C1425FQB Buenos Aires, Argentina
3
Centro Regional Universitario Bariloche, Universidad Nacional del Comahue, 8400 S.C. de Bariloche, Río Negro, Argentina
power reactor fuels. They reported formation of intermediate uranium fluorides, including UO2F2(s), among others [1]. Fluorination of UO2(s) in CF4(g)/O2(g) plasma was investigated by Kim et al. [5], who found that the main reaction product was UF6 and identified an oxyfluoride compound, possibly UO2F2(s), as a reaction intermediate by XPS. Yang et al. studied the plasma etching of uranium oxide films and identified the formation of U OF2(s), UO2F2(s) and U OF4(s) at the surface of the UO2(s) film by XPS [6]. Only a few papers report basic kinetic data for the fluorination of uranium oxides [7]. The reactions of U 3O8(s) and UO3(s) with fluorin
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