Oxalic Precipitation for Uranium and Actinide Recovery
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Solution Overview
Problem
Current processes for treating spent nuclear fuels, such as PUREX and COEX ™, require multiple operations from dissolving fuels in nitric acid to obtaining a usable mixed oxide powder for MOX fuel production, which is inefficient and increases the risk of contamination.
Innovation Solution
A process involving back-extraction of uranium(VI) and actinide(IV) from an organic solution using an aqueous solution with controlled concentrations of nitric acid and oxalic acid, allowing for the precipitation of actinide(IV) and a fraction of uranium(VI) in a controlled U(VI)/actinide(IV) ratio without prior dilution of the organic phase.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple separate operations are used for dissolution, separation, purification, and conversion in PUREX and COEX processes, then recovery and purification of uranium and plutonium can be achieved, but the number of operations increases and the risk of contamination increases
Solution Approach 1:
The patent combines multiple separate operations (dissolution, separation, purification, and conversion) into a single integrated oxalic precipitation step. By using oxalic acid to simultaneously precipitate plutonium from the organic phase while controlling uranium co-precipitation, the process achieves both separation and purification in one operation, directly reducing the number of steps while maintaining recovery and purification effectiveness
Solution Approach 2:
The oxalic precipitation step serves multiple functions simultaneously: it acts as a separation step (partitioning Pu and U), a purification step (removing impurities), and a conversion step (producing oxalate precipitate ready for calcination to mixed oxide). This multi-functionality eliminates the need for sequential separate operations, reducing process complexity while maintaining reliability
2Reliability
If multiple separate operations are used for dissolution, separation, purification, and conversion in PUREX and COEX processes, then recovery and purification of uranium and plutonium can be achieved, but the risk of contamination increases
Solution Approach 1:
By merging multiple operations into one integrated oxalic precipitation step, the patent minimizes the number of transfer steps and intermediate handling operations where contamination could occur. The single-step process reduces exposure to environmental contaminants and minimizes opportunities for operational errors that could lead to contamination
Solution Approach 2:
The patent extracts both plutonium and uranium simultaneously from the organic phase in one precipitation operation, removing them together as a controlled mixture rather than through multiple separate extraction steps. This reduces the cumulative risk of contamination that would accumulate through multiple sequential operations
3Quantity of substance
If conventional oxalic precipitation is used without controlling oxalic acid concentration and O/A ratio, then actinide(IV) can be precipitated, but the U(VI)/actinide(IV) ratio in the precipitate is uncontrolled and impurities increase
Solution Approach 1:
The patent precisely controls the concentration of oxalic acid (1.0-3.0 mol/L) and the organic/aqueous volume ratio (0.5-2.0) to optimize the precipitation process. By adjusting these parameters, the process achieves complete actinide precipitation while controlling uranium co-precipitation to achieve the desired U(VI)/actinide(IV) ratio in the precipitate, minimizing impurities and ensuring manufacturing precision
Solution Approach 2:
The patent establishes specific parameter ranges for oxalic acid concentration and O/A ratio based on the initial U/Pu ratio in the organic phase. This feedback-controlled approach ensures that the precipitation conditions are optimized according to the feed composition, maintaining controlled U(VI)/actinide(IV) ratios and high purity precipitate across varying input conditions
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 reduces the number of operations needed to produce a usable mixed oxide powder, achieving a controlled U(VI)/actinide(IV) ratio and minimizing impurities, thus enhancing the efficiency and purity of the MOX fuel production process.
Implementation Method 1
back-extracting, from an organic solution comprising uranium(VI) and an actinide(IV), all or almost all of the actinide(IV), together with a fraction of the uranium(VI), in a controlled U(VI)/actinide(IV) ratio, by oxalic precipitation
Data Source
Figure 1~2
Figure 3
AI summary
The invention relates to a process for extracting U(VI) and an actinide(IV) from an organic solution in which the U(VI) and actinide(IV) are present as nitrates at concentrations such that the concentration of U(VI) nitrate is greater than the concentration of actinide(IV) nitrate, and the sum of the concentrations of U(VI) and actinide(IV) nitrates is ≥ 55 g/L, the organic solution comprising TBP in an organic diluent, which process comprises: - at least one contacting of the organic solution with an aqueous solution comprising 2 mol/L to 6 mol/L of nitric acid and oxalic acid at a concentration ≥ 18 g/L in an O/A volume ratio ≥ 1, the concentration of oxalic acid and the O/A volume ratio being chosen such that the oxalic acid is deficient with respect to the stoichiometric conditions for complete precipitation of U(VI) and actinide(IV),whereby a precipitate is obtained comprising actinide(IV) as oxalate and U(VI) as oxalate in a U(VI)/actinide(IV) mass ratio between 0.5 and 5; then – separation of the precipitate from the organic and aqueous solutions. It also relates to a process for treating an aqueous solution obtained from the dissolution of spent nuclear fuel in nitric acid, in which this de-extraction process is implemented.