Vacuum Distillation Enhances Nuclear Fuel Solvent Recycling Efficiency

In nuclear fuel reprocessing, solvents function as tireless "cleaners," working day after day to extract valuable uranium and plutonium from spent fuel. However, these molecular workhorses gradually degrade under prolonged exposure to intense radiation and corrosive chemicals, losing efficiency and potentially generating harmful byproducts that compromise both safety and processing effectiveness.

The solution lies in solvent regeneration technology. At nuclear reprocessing facilities, the hydrocarbon-tributyl phosphate (TBP) solvent system plays a critical role. Over time, interactions between nitric acid, nitrous acid, and hydrocarbons under radiation produce various degradation products that impair extraction performance and process stability. Developing efficient regeneration methods to remove these contaminants has become essential for maintaining operational reliability.

While traditional methods like chemical washing and adsorption have limitations in efficiency and waste generation, vacuum distillation has emerged as a promising physical separation technique. This approach offers operational simplicity, high separation efficiency, and environmental benefits by avoiding secondary waste.

The technology leverages differences in boiling points under reduced pressure, enabling separation at lower temperatures that prevent TBP decomposition while effectively removing impurities. However, TBP's thermal instability and the extremely low concentrations of diverse contaminants present significant engineering challenges, requiring precisely controlled systems.

Researchers at the Reprocessing Development Laboratory of the Indira Gandhi Atomic Research Centre have developed and validated a pilot-scale solvent purification system based on vacuum distillation. This integrated solution combines multiple liquid-gas separation units into a comprehensive regeneration process:

• Dehydration Column: Initially removes water content that could affect extraction efficiency and cause equipment corrosion through distillation principles.
• Agitated Thin-Film Evaporator: Creates a heated thin film for rapid solvent evaporation while preventing thermal decomposition, with vapor directed to the vacuum distillation column.
• Vacuum Distillation Column: The system's core, where multiple vapor-liquid contacts under vacuum separate pure TBP (collected at the top) from degradation products (retained at the base).

Testing with simulated degraded solvents evaluated physical properties (density, viscosity) and extraction performance (uranium/plutonium recovery rates), providing critical data for process optimization.

• Vacuum operation reduces boiling points to preserve TBP integrity
• Integrated multi-stage separation for comprehensive purification
• Precision control of temperature, pressure, and flow parameters

This breakthrough offers nuclear facilities an effective method to extend solvent lifespans, reduce costs, minimize waste, and enhance operational safety. The technology also shows potential for adaptation in chemical and pharmaceutical industries for solvent recovery applications.

• Further optimization of operating parameters
• Development of advanced separation materials
• Implementation of automated control systems

As vacuum distillation technology continues to evolve, it promises to revitalize these molecular "cleaners," supporting more sustainable nuclear fuel reprocessing operations worldwide.