Fluoride Molten Salt Separation of Actinides from Oxide Fuels
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Solution Overview
Problem
Current reprocessing methods for spent nuclear fuel, such as the PUREX process, face challenges including potential proliferation risks, sensitivity to irradiation, and difficulties with refractory fuels, while pyrochemical processes using molten salt media face issues with long-term chloride waste confinement and the need for hydrofluorination steps.
Innovation Solution
A process involving a molten salt medium containing fluoride, specifically MF—AlF3, where M is an alkaline element, allows for the direct separation of chemical elements from oxide form without prior conversion to fluorides, using a reducing metal to selectively extract actinides from other elements, thereby avoiding hydrofluorination and enhancing safety and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If chloride molten salt medium is used for pyrochemical reprocessing, then corrosion problems are easier to manage and lower operating temperatures can be used, but long-term confinement of chloride waste becomes problematic
Solution Approach 1:
The invention changes the chemical composition parameter of the molten salt medium from chloride-based to fluoride-based (specifically LiF-AlF3 eutectic mixture), thereby transforming the waste product from problematic chloride waste to manageable fluoride waste that can be directly vitrified in glass confinement matrices
Solution Approach 2:
The invention converts the previously harmful fluoride waste product into a beneficial intermediate that is directly compatible with glass confinement matrices, allowing the waste to be seamlessly integrated into the final waste form without requiring separate treatment
2Object-affected harmful factors
If fluoride molten salt medium is used for pyrochemical reprocessing, then waste is directly compatible with glass confinement matrix, but hydrofluorination step is required before processing
Solution Approach 1:
The invention performs preliminary conversion of the molten salt composition to a fluoride-based system (LiF-AlF3) that inherently accepts oxide inputs, eliminating the need for preliminary hydrofluorination of the fuel and streamlining the process flow
Solution Approach 2:
The fluoride-based molten salt medium serves multiple functions: it dissolves oxide fuels directly without pre-treatment, enables selective separation of actinides, and produces waste compatible with glass confinement, thereby consolidating multiple process requirements into a single versatile medium
3Reliability
If PUREX process is used for reprocessing, then reliable and robust separation is achieved, but proliferation risks increase and refractory fuels cannot be processed
Solution Approach 1:
The invention replaces the chemical extraction mechanism of PUREX with a pyrochemical reduction mechanism using liquid metal in fluoride molten salt, fundamentally changing the separation principle while maintaining reliability and eliminating proliferation risks associated with pure plutonium recovery
Solution Approach 2:
The invention changes the fundamental operating parameters from aqueous-organic extraction at moderate temperatures to high-temperature pyrochemical reduction, thereby altering the chemical reactions and separation mechanisms to achieve both reliability and non-proliferation goals
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 method enables effective separation of actinides from fission products without the need for hydrofluorination, reducing proliferation risks and improving the handling of refractory fuels, with high recovery rates and selectivity between actinides and fission products, suitable for reprocessing spent nuclear fuel and other nuclear materials.
Implementation Method 1
a step to solubilise a powder of one or more oxides of the said at least one first chemical element E1 and a powder of one or more oxides of the said at least one second chemical element E2 in a medium comprising at least one molten salt of formula MF—AlF3
Implementation Method 2
a step to contact the mixture resulting from step a) with a medium comprising a metal in liquid state, said metal being a reducing agent capable of predominantly reducing the said at least one first chemical element E1
Data Source
AI summary
The invention pertains to a process for separating at least one first chemical element E1 from at least one second chemical element E2 coexisting in a mixture in the form of oxides, comprising the following steps:a) a step to solubilise a powder of one or more oxides of the said at least one first chemical element E1 and a powder of one or more oxides of the said at least one second chemical element E2 in a medium comprising at least one molten salt of formula MF—AlF3 wherein M is an alkaline element, after which there results after this step a mixture comprising the said molten salt, a fluoride of the said at least one first chemical elements E1 and a fluoride of the said at least one second chemical element E2;b) a step to contact the mixture resulting from step a) with a medium comprising a metal in the liquid state, the said metal being a reducing agent capable of predominantly reducing the said at least one first chemical element E1 relative to the said at least one second chemical element E2, after which there results after this step a two-phase medium comprising a first phase called metal phase comprising the said at least one first chemical element E1 in oxidation state 0, and a second phase called saline phase comprising the molten salt of above-mentioned formula MF—AlF3 and a fluoride of the said at least one second chemical element E2.