PUREX Method Single-Cycle Uranium-Actinide Separation
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Solution Overview
Problem
The existing PUREX method for reprocessing spent nuclear fuels requires multiple purification cycles to separate uranium from neptunium, increasing costs and complexity, and uses powerful sequestrants that can generate undesirable products in aqueous effluents.
Innovation Solution
A method that uses a water-immiscible solvent to co-extract uranium and actinides from an aqueous nitric solution, followed by back-extraction and concentration steps to enrich the solvent phase with uranium, allowing for the separation of actinides, including neptunium, in a single purification cycle without the need for additional sequestrants.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multiple purification cycles are used to separate uranium from neptunium, then separation completeness is improved, but process complexity and cost increase
Solution Approach 1:
The invention changes the chemical parameters of the aqueous phase by controlling nitric acid concentration and adding specific agents (hydrazine, uranous nitrate) to modify the oxidation states and extraction behavior of actinides. This allows neptunium to be selectively back-extracted into the aqueous phase while uranium remains in the organic phase, achieving complete separation in a single cycle without complex multi-step processes
Solution Approach 2:
The invention extracts neptunium selectively from the co-extracted mixture of uranium and neptunium by back-extraction into an aqueous phase. The neptunium is taken out from the organic phase containing both actinides, leaving pure uranium behind, thus achieving separation without requiring multiple purification cycles
2Productivity
If powerful sequestrants are used to separate neptunium, then separation efficiency is improved, but undesirable products are generated in aqueous effluents
Solution Approach 1:
The invention uses inexpensive, easily decomposable agents such as hydrazine and uranous nitrate instead of powerful sequestrants. These agents perform the separation function temporarily and then decompose or can be easily removed, avoiding the generation of persistent undesirable products in the aqueous effluents that would result from using strong chelating agents
Solution Approach 2:
The invention converts the potential harm of using reducing agents (which could generate unwanted byproducts) into a benefit by carefully controlling the reduction of neptunium to a specific oxidation state that enables selective back-extraction. The reducing agents used (hydrazine, uranous nitrate) are consumed in the process and do not leave harmful residues, transforming a potentially problematic step into an effective separation mechanism
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 approach efficiently separates uranium from other actinides in a single cycle, eliminating the need for a second uranium cycle and minimizing the use of sequestrants, thereby reducing costs and simplifying the reprocessing process while maintaining high reprocessing yield and quality.
Implementation Method 1
co-extraction of uranium(VI), plutonium(IV) and other actinides(IV) or (VI) from said aqueous solution by using a water-immiscible solvent phase comprising at least one extractant in an organic diluent
Implementation Method 2
back-extraction of the plutonium(III) from the solvent phase by using an aqueous nitric solution which contains a reducing agent capable of reducing plutonium(IV) to oxidation state (III)
Data Source
AI summary
The invention relates to a method constituting an improvement of the PUREX method, which makes it possible to obtain separation of uranium from the other actinides (Pu, Np, Th, . . . ) in a single purification cycle.This method successively comprises: a) co-extracting the uranium(VI), plutonium(IV) and other actinides(IV) or (VI) from an aqueous nitric solution by using solvent phase and scrubbing the latter; b) back-extracting the plutonium in oxidation state (III) from the solvent phase by using an aqueous nitric solution; c) back-extracting the uranium in oxidation state (VI) from the solvent phase by using an aqueous nitric solution; d) concentrating the aqueous nitric solution resulting from step c) with respect to uranium(VI); and it is characterized in that some of the uranium(VI)-concentrated aqueous solution obtained in step d) is used for back-extracting the actinide(IV) or actinides(IV) from the solvent phase during step b) or between steps b) and c).Uses: reprocessing of spent nuclear fuels based on UO2, (U,Pu)O2 or (U,Th)O2 mixed oxide.