Liquid Cadmium Cathode Actinide Recovery
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Solution Overview
Problem
Conventional methods for recovering residual actinide elements from chloride molten salts face challenges such as complex apparatus construction, low efficiency, and high radiation waste generation, particularly in large-scale pyroprocessing, due to high specific gravity differences between molten salts and liquid metals, and inefficiencies in electrochemical recovery processes.
Innovation Solution
A hybrid process using liquid cadmium cathode (LCC) electrolysis and CdCl2 oxidant for electro-deposition and oxidation of actinide elements in chloride molten salts, allowing for the reduction of actinide concentrations to 100 ppm or less without requiring additional equipment, and enabling the reuse of existing electro-winning apparatuses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a multi-staged reductive extraction apparatus is constructed to recover residual actinide elements from waste molten salts, then recovery efficiency is improved, but device complexity and operational difficulty increase significantly due to the need for three to five stages with countercurrent flow and high specific gravity differences between molten salt and liquid metal
Solution Approach 1:
The patent divides the recovery process into two distinct stages: (1) electro-winning stage using liquid cadmium cathode to recover actinide elements, and (2) reductive extraction stage using organic solvent to recover rare-earth elements. This segmentation allows each stage to be optimized independently, avoiding the need for complex multi-staged countercurrent flow apparatus while maintaining high recovery efficiency for both element groups
Solution Approach 2:
The patent introduces an organic solvent as an intermediary medium in the reductive extraction stage. The organic solvent selectively extracts rare-earth elements from the molten salt through redox reactions, acting as a mediator that simplifies the separation process and eliminates the need for complex multi-staged apparatus designed for direct liquid metal-molten salt contact
2Quantity of substance
If a multi-staged reductive extraction apparatus is constructed for treating large amounts of waste molten salt, then recovery capacity is improved, but operational complexity increases and continuous operation becomes difficult
Solution Approach 1:
The patent employs a simple two-stage process where each stage naturally progresses without complex operational interventions. The electro-winning stage automatically deposits actinides on the liquid cadmium cathode, and the subsequent reductive extraction stage automatically separates rare-earth elements using the organic solvent. This self-service mechanism allows continuous processing of large volumes without the operational difficulties associated with multi-staged countercurrent flow apparatus
Solution Approach 2:
The patent changes the chemical parameters of the system by introducing an organic solvent with specific redox properties that can selectively react with rare-earth elements. This parameter change transforms the complex physical separation problem into a simpler chemical separation process, enabling easy continuous operation for large-scale waste molten salt treatment
3Device complexity
If electrochemical recovery method using solid cathode is used to recover residual actinide elements, then equipment simplicity is improved, but recovery efficiency decreases due to disproportionation reaction between electrodeposited metal and trivalent ions
Solution Approach 1:
The patent changes the physical state parameter of the cathode from solid to liquid, creating a liquid cadmium cathode. This parameter change eliminates the disproportionation reaction problem that occurs with solid cathodes, as the liquid metal cathode maintains a different electrochemical potential that prevents the unwanted reaction between electrodeposited metal and trivalent ions, thereby maintaining high recovery efficiency while keeping equipment relatively simple
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 effectively reduces residual actinide concentrations in waste molten salts, minimizing high radiation waste and improving processing efficiency and economic advantages by simplifying the recovery process and avoiding complications in multi-staged reductive extraction methods.
Implementation Method 1
electro-depositing the actinide elements contained in the chloride molten salt on the LCC
Implementation Method 2
oxidize the rare-earth elements co-deposited on the LCC, thereby forming the rare-earth chlorides in the chloride molten salt
Data Source
AI summary
A method for recovery of residual actinide element from chloride molten salts that are formed after electro-refining and/or electro-winning of a spent nuclear fuel and include actinide elements and rare-earth elements is provided. The method comprises conducting electrolysis using a liquid cadmium cathode (LCC) in the chloride molten salt that is formed after electro-refining and/or electro-winning of a spent nuclear fuel and contains rare-earth elements and actinide elements; electro-depositing the actinide elements contained in the chloride molten salt on the LCC in order to reduce a concentration of the actinide elements; and adding a CdCl2 oxidant to the chloride molten salt containing the LCC-metal alloy in order to oxidize the rare-earth elements co-deposited on the LCC, thereby forming the rare-earth chlorides in the chloride molten salt.