Magnesiothermic reduction kinetics of UF 4
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Magnesiothermic reduction kinetics of UF4 Renu Agarwal1 · Amulya Raina2 · Neeraj Kumar Gupta3 Received: 13 November 2018 / Accepted: 12 October 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract The most popular method for production of metallic uranium is by magnesiothermic reduction of U F4. Efficient production of good quality uranium metal chunk in the reaction vessel requires multiple parameter constraints. To theoretically optimize these process parameters, many basic properties, i.e. particle size, heat dissipation, packing density, heating rate, kinetic parameters of reaction, etc., are required. There was lack of information on kinetic parameters of this reaction; therefore, kinetic triplets of U F4 and magnesium metal reaction were determined by non-isothermal DTA method, at 5–20 K min−1 heating rates. The analysis of data was done by model-less methods and model-fitting methods. It was found that the reaction takes place through two parallel competitive mechanisms, bulk diffusion and first-order nucleation and growth of reaction sites, and the corresponding kinetic parameters, frequency factors and activation energies, were 440 min−1, 43.9 kJ mol−1, 420 min−1 and 49.03 kJ mol−1, respectively. Keywords Non-isothermal kinetics · Activation energy · Uranium fluoride · Magnesium · Differential thermal analysis
Introduction Uranium metal is a basic material required for the fabrication of many metallic nuclear fuels, U, U3Si2, (U, Al), (U, Pu), (U, Zr), (U, Mo), etc. Several methods are used for production of uranium metal, and common among them are: (1) electrochemical reduction of chlorides, fluorides or oxides of uranium into metal and (2) metallothermic reduction of U F 4. The latter method is one of the oldest and the most popular methods used till date for largescale production of reactor grade uranium metal [1–3]. Metallothermic reduction of U F4 is carried out by using magnesium or calcium. Calciothermic reduction has many advantages over magnesiothermic reduction as the reaction yield is higher in former. The enthalpy of calciothermic reduction, at 1000 K, is − 524.2 kJ mol−1 (U) as compared to − 341.6 kJ mol−1 (U) during magnesiothermic reduction * Renu Agarwal [email protected] 1
Fuel Chemistry Division, Bhabha Atomic Research Centre, Mumbai 400085, India
2
Uranium Extraction Division, Bhabha Atomic Research Centre, Mumbai 400085, India
3
Product Development Division, Bhabha Atomic Research Centre, Mumbai 400085, India
[4]. However, calcium is costlier than magnesium, but the main disadvantage of using calcium metal for reduction is pyrophoric nature of pure calcium metal, requiring storage and handling of the metal in inert atmosphere glove boxes. Therefore, magnesiothermic reduction of uranium fluoride to produce uranium metal on industrial scale is preferred. The reaction is carried out in a closed reactor, under inert gas atmosphere. The firing temperature is an important parameter for getting complete reduction and good quality uranium metal. The firing temper
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