Actinide Oxide Powder Preparation via Cryogenic Granulation
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Solution Overview
Problem
Existing methods for preparing actinide oxide powders, particularly plutonium oxide (PuO2), face challenges such as fine particle dispersal, filter clogging, and homogeneity issues, which affect the quality and efficiency of nuclear fuels and transmutation targets.
Innovation Solution
A method involving cryogenic granulation of an aqueous solution containing actinide cations followed by freeze-drying and calcination, eliminating the need for oxalic precipitation and filtration, and ensuring homogeneous distribution and reduced fine particle content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If oxalic precipitation and filtration methods are used to prepare plutonium oxide powder, then plutonium can be recovered from nitric solutions, but fine particle dispersal occurs and filters become clogged
Solution Approach 1:
The patent employs phase transition by precipitating plutonium as hydroxide instead of oxalate, which dissolves more readily in nitric acid. This phase change approach allows plutonium to be recovered without forming fine dispersible particles that clog filters, thus resolving the contradiction between ease of manufacture and harmful fine particle generation
Solution Approach 2:
The patent changes the chemical parameters of the precipitation process by using hydroxide precipitation with controlled pH and nitric acid concentration rather than oxalic acid precipitation. This parameter change results in a plutonium compound that dissolves completely without forming fine particles, eliminating filter clogging while maintaining ease of plutonium recovery
2Ease of manufacture
If mechanical mixing methods are used to prepare mixed oxide powders, then uranium and plutonium oxides can be mixed, but homogeneous distribution of elements is difficult to achieve
Solution Approach 1:
The patent merges uranium and plutonium into a single homogeneous nitric solution before precipitation, rather than mixing separate oxide powders. This merging at the molecular level in solution ensures complete homogeneity of element distribution, which is then maintained through the precipitation process, resolving the contradiction between ease of manufacture and manufacturing precision
Solution Approach 2:
The patent uses hydraulic mixing by preparing a homogeneous nitric acid solution containing both uranium and plutonium nitrates. This liquid-phase hydraulic mixing ensures uniform distribution at the molecular level, achieving superior homogeneity compared to mechanical powder mixing while maintaining ease of manufacture
3Manufacturing precision
If complete grinding of UO2 and PuO2 powders is performed to ensure intimate mixing, then homogeneous distribution is achieved, but fine particle content increases causing particle dispersal
Solution Approach 1:
The patent inverts the conventional approach by dissolving the oxides in nitric acid to form a homogeneous solution, then precipitating the mixed oxides directly as granules. This inversion eliminates the need for grinding and intimate mixing of fine powders, achieving homogeneous distribution without generating dispersible fine particles
Solution Approach 2:
The patent uses phase transition from dissolved state to precipitated granular state to directly form mixed oxide particles with desired size distribution. This phase transition approach bypasses the grinding process entirely, achieving intimate mixing at the molecular level in solution and then forming non-dispersible granules upon precipitation
4Object-generated harmful factors
If limited grinding of powders is performed, then fine particle dispersal is reduced, but homogeneous mixing of elements is compromised
Solution Approach 1:
The patent performs preliminary mixing at the molecular level in the nitric acid solution before precipitation. This preliminary action ensures complete homogeneity of uranium and plutonium distribution, which is then locked in during precipitation. No subsequent grinding is needed, thus reducing fine particle dispersal while maintaining manufacturing precision
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
The method produces powders with excellent flowability, compactability, and sinterability, minimizing fine particle dispersal and enhancing element homogeneity, suitable for nuclear fuels and transmutation targets.
Implementation Method 1
a) cryogenic granulation of an aqueous solution comprising cations selected from uranium-based cations, plutonium-based cations, and minor actinide-based cations
Implementation Method 2
b) freeze-drying the granules obtained in a)
Implementation Method 3
freeze-drying the granules obtained in a)
Implementation Method 4
c) calcining the granules obtained from b); whereby the powder is obtained
Data Source
AI summary
A method for preparing a powder including one or more oxides selected from uranium oxide UO2, plutonium oxide PuO2 and minor actinide oxides, the minor actinides being selected from americium, neptunium and curium, including steps of: a) cryogenic granulation of an aqueous solution comprising cations selected from uranium-based cations, plutonium-based cations, and minor actinide-based cations; b) freeze-drying the granules obtained in a); and c) calcining the granules obtained from b). The method can be used to manufacture nuclear fuels or blankets charged with minor actinide(s).