The use of organic extractants in solvent extraction processes in the partitioning of spent nuclear fuels

The partitioning of spent nuclear in an effective, safe, and proliferation-resistant manner is considered by many to be of key importance for the future sustainability and possible expansion of nuclear power in the energy mix. Many solvent-extraction processes, applying various organic molecules, have been proposed and tested for the partitioning of actinides from spent nuclear fuel with varying degrees of success. The most successful of these processes is the PUREX (Plutonium URanium EXtraction) process, which has been used for large-scale separation of uranium and plutonium from spent nuclear fuel. However, for the majority of these established processes a thorough understanding of how the organic extractant molecules interact with relevant metal ion species is lacking. New processes like the SANEX (selective actinide extraction) process for minor actinide/lanthanide separations are being considered for next-generation partitioning of spent nuclear fuel where a significant body of work on understanding metal ion speciation with proposed extractants is being used to support the development of these novel procedures. This chapter provides a brief overview of established and new solvent-extraction processes, and the methods used to study metal ion speciation with extractant molecules. This is followed by an extensive review of the speciation work relevant to minor actinide/lanthanide separations for the SANEX process and how this work is assisting in the design of improved extractant molecules.