Hydrothermal Conversion of Uranium Oxide to Nanocrystalline UO2
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Solution Overview
Problem
Current methods for producing uranium dioxide nanoparticles are energy-intensive, require multiple steps, and face challenges in scalability and yield, particularly in converting uranium oxides directly into UO2+x nanoparticles with controlled morphology.
Innovation Solution
A hydrothermal conversion process involving uranium oxide, a carbonate salt, hydrogen peroxide, oxalic acid, and a reducing agent in an aqueous solution, heated between 90°C and 250°C under pressure, to produce nanocrystalline uranium dioxide nanoparticles with controlled size and morphology.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a focused powerful CO2 laser beam is used to convert UO2 into UO2+x nanoparticles, then nanoparticles can be obtained through condensation of oversaturated vapour, but the process requires 1000 W laser power which is energy intensive and expensive to implement
Solution Approach 1:
The patent replaces the mechanical/physical laser heating system with a chemical hydrothermal system. Instead of using a 1000 W CO2 laser beam to evaporate UO2 and condense vapour into nanoparticles, the invention uses hydrothermal treatment where UO2 is heated in an aqueous environment with carbonate salts and reducing agents to directly form UO2+x nanoparticles through chemical reactions and controlled precipitation.
Solution Approach 2:
The patent changes the fundamental parameters of the conversion process by transitioning from high-temperature laser evaporation (requiring 1000 W power) to hydrothermal treatment at lower temperatures (typically below 300°C). The process parameters are changed from laser power and vapour condensation control to aqueous solution chemistry, pH control, and hydrothermal conditions, enabling nanoparticle formation with much lower energy input.
2Manufacturing precision
If a focused laser beam is used to heat the sample surface, then UO2+x nanoparticles can be formed through vapour condensation, but the surface area heated is only 1 mm2 which limits productivity
Solution Approach 1:
The patent applies a universal hydrothermal treatment that can process bulk quantities of UO2 powder simultaneously throughout the entire sample mass, rather than the laser method which only treats a tiny 1 mm2 surface area at a time. The aqueous hydrothermal environment penetrates and reacts with the entire uranium oxide sample, enabling multi-functional processing that combines dissolution, reduction, and nanoparticle formation in a single step across the whole material volume.
Solution Approach 2:
The patent segments the conversion process into chemical steps (dissolution of UO2, reduction to U(IV), precipitation of UO2+x nanoparticles) that occur simultaneously throughout the bulk material in the hydrothermal environment, rather than requiring sequential processing of small surface areas. This allows parallel processing of the entire sample volume, dramatically increasing productivity while maintaining nanoparticle quality.
3Use of energy by moving object
If uranium oxide pellets are shaped and sintered before laser treatment, then a focused laser beam can be applied, but the process becomes multistep and complex
Solution Approach 1:
The patent eliminates the need for preliminary pellet shaping and sintering steps by directly treating loose UO2 powder in the hydrothermal environment. The aqueous solution and reducing agents penetrate the powder directly, converting it to UO2+x nanoparticles without requiring the material to be first formed into dense pellets. This reverses the conventional sequence by removing preparatory steps rather than adding them.
Solution Approach 2:
The patent merges multiple process steps (pellet shaping, sintering, laser heating, vapour condensation) into a single hydrothermal treatment step. The aqueous environment simultaneously provides heating, chemical reduction, and nanoparticle formation conditions, consolidating what would otherwise require separate operations into one integrated process that reduces both complexity and equipment requirements.
4Manufacturing precision
If hydrothermal decomposition of actinide oxalates is used to obtain nanocrystals, then nanoscale properties can be achieved, but the process requires multiple steps including precipitation and calcination
Solution Approach 1:
The patent performs preliminary reduction of U(VI) to U(IV) in the aqueous solution before nanoparticle formation, eliminating the need for subsequent calcination steps required in oxalate decomposition methods. By pre-forming UO2 or UO2+x nuclei in the hydrothermal environment through controlled reduction and precipitation, the process achieves nanoparticle formation in a single step without requiring high-temperature calcination to remove organic oxalate residues.
Solution Approach 2:
The patent extracts and eliminates the organic oxalate intermediate step from the conventional synthesis route. Instead of forming uranium oxalate complexes that require calcination to decompose, the method directly reduces uranium in aqueous solution and precipitates inorganic UO2+x nanoparticles, removing the organic component entirely and eliminating the associated decomposition step and equipment requirements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This process simplifies the production of UO2+x nanoparticles, allowing for direct conversion from uranium oxide powders without prior treatment, achieving high purity and controlled particle size, and is more industrially scalable, improving the recycling of uranium fuel production scraps.
Implementation Method 1
The process consists in contacting said uranium oxide with a carbonate salt and hydrogen peroxide in water
Implementation Method 2
contacting said uranium oxide with a carbonate salt and hydrogen peroxide in water
Implementation Method 3
heating the reactional mixture between 90°C and 250°C under pressure to produce nanocrystalline uranium dioxide nanoparticles
Implementation Method 4
produce nanocrystalline uranium dioxide nanoparticles
Implementation Method 5
adding a reducing agent to said aqueous solution
Data Source
Figure 1~1b
Figure 2
Figure 3
AI summary
The present invention concerns the preparation of crystalline nanoparticles of uranium dioxide and hyper-stoichiometric uranium dioxide by hydrothermal conversion of an uranium oxide, the nanocrystalline particles obtainable therefrom and the use of the process for tuning the size and morphology of uranium oxide and hyper-stoichiometric uranium dioxide.