A novel method for stoichiometric reduction of (U 3 O 8 ,PuO 2 ) and its controlled oxidation using microwave

Tetra-uranium fluoride electrowinning by electro-electrodialysis cell (EED)

This article shows the modeling of a uranium dioxide production reactor using COMSOL Multiphysics software program in its 4.3b version. The model was made using 3 kinds of studies: momentum, heat and mass transport, in order to determine the influence of the most important operational parameters: UO3 reaction rate, composition and flow of the reduction gas, the initial temperature reactor and the reducing gas. The operational parameters evaluated were the followings: constant gas flow of2.5 L/min, initial hydrogen concentration of 0.25, 0.50 and0.75 M, and initial temperature of 400°C. The obtained results allow to conclude that under these working conditions, uranium dioxide is obtained virtually instantaneous and, with concentrations close to 0.5 M H2 in the reducing gas, the process can operate continuously and autogenously, without applying additional energy and temperatures around 600°C.

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Modeling Operational Parameters for Uranium Dioxide Production Reactor through Uranium Trioxide Reaction Using Hydrogen

This paper presents a study on the process engineering aspects of relevance to the industrial implementation of ThO2 and (Th, U)O2 mixed oxide (MOX) pellet type fuel manufacturing. The paper in particular focuses on the recycling of thoria based fuel production scrap which is an economically important component in the fuel manufacturing process. The thoria based fuels are envisaged for Advanced Heavy Water Reactor (AHWR) and other reactors important to the Indian Nuclear Power Programme. A process was developed for recycling the chemically clean, off-specification and defective sintered ThO2 and (Th, U)O2 MOX nuclear fuel pellets. ThO2 doesn’t undergo oxidation or reduction and thus, more traditional methods of recycling are impractical. The integrated process was developed by combining three basic approaches of recycling namely mechanical micronisation, air oxidation (for MOX) and microwave dissolution-denitration. A thorough investigation of the influence of several variables as heating method, UO2 content, fluoride and polyvinyl alcohol (PVA) addition during microwave dissolution-denitration was recorded on the product characteristics. The suitability evaluation of the recycled powder for re-fabrication of the fuel was carried out by analyzing the particle size, BET specific surface area, phase using XRD, bulk density and impurities. The physical and chemical properties of recycled powder obtained from the sintered (Th1-y, Uy)O2 (y; 0 - 30 wt%) pellets advocate 100% utilisation for fuel re-fabrication. Recycled ThO2 by integrated process showed distinctly high sinterability compared to standard powder evaluated in terms of surface area and particle size.

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An Integrated Process for Recycling of ThO 2 Based Mixed Oxide Rejected Nuclear Fuel Pellets

The invention discloses a preparation method of a uranium dioxide nano material, and belongs to the technical field of nano materials. The preparation method comprises the following steps: uniformly mixing a uranyl nitrate solution and a sodium hydroxide solution, adding the mixture into a reaction kettle for hydrothermal reaction, cooling the reaction product to room temperature, washing the reaction product with water until the pH value is 7.5-8.5, drying and grinding the reaction product, putting the obtained powder into a tubular furnace, and introducing hydrogen for reduction, thereby obtaining the uranium dioxide nano material. By utilizing the preparation method of the uranium dioxide nano-material, UO2 ceramic nano-powder with controllable morphology, light agglomeration, uniform particle size, high specific surface area and good catalytic activity can be prepared on a large scale.

Preparation method of thorium dioxide nano material

This article presents a study on the kinetics of the uranium conversion process, consisting in the reduction of uranium trioxide to uranium dioxide using hydrogen gas at temperatures of 500°C, 600°C and 700°C. Hydrogen concentrations used in the flow were 0.25 M, 0.50 M and 0.75 M. The mechanism established for the study of the kinetics of reduction of uranium trioxide was through the formation of an intermediate compound, U3O8. For this reason, these tests were divided into 2 stages: the first one the reduction from UO3 to U3O8, and second one from U3O8 to UO2. The results of each test were quantified by the release of H2O(g) produced by both reactions. Tests showed that the ideal working conditions are for hydrogen concentration flows of 0.75 M and temperatures in the range of 500°C - 600°C, with the intent to decrease the occurrence of side reactions that interfere with the process.

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Pedro Orrego Alfaro

Papers

Reduction Kinetics of Uranium Trioxide to Uranium Dioxide Using Hydrogen