Liquid-liquid extraction of plutonium: third phase, molecular modelling and molecular theory

About the Project

This project concerns the liquid-liquid of extraction of plutonium, which is important to energy, defence, space power and waste disposal. For example, closing the nuclear fuel cycle by reprocessing spent nuclear fuel to remove plutonium reduces the volume and heat load of high-level waste, improves the efficiency of uranium reserves and may enable the future use of mixed oxide fuel. The extraction process involves the transfer of plutonium ions, dissolved in nitric acid, to plutonium complexes in an organic phase. The plutonium may then be isolated from this organic phase. At high loadings, these plutonium complexes stick together to form an extended gel-like phase, called the third phase. Why this happens is both unknown and intriguing, but from a practical viewpoint, third phase formation is a processing disaster! This project will involve the use of atomistic Molecular Dynamics simulation to shed light on how and why this third phase forms and then, building on the insights gained, to investigate a range of organic solutes to identify the characteristics that would reduce the propensity for third phase formation. In addition to the computational work, we will also develop new molecular thermodynamic models, based on those proposed for aqueous systems by Nagarajan et al. and Danov et al., to provide a theoretical framework that describes aggregate and third phase formation, which can then be fed into future process-level flowsheet models.

This project is part of the Nuclear Doctoral Focal Award in Radiation Protection, Nuclear Safety and Environmental Sustainability (RAPTOR). The successful candidate will be part of a cohort of PhD students across four universities (Manchester, Liverpool, Surrey, Suffolk) working in a national programme with 18 industrial partners. During the first months of this PhD, training will be provided UK experts in radiation protection, environmental assessment and radioactive waste management, nuclear safety and security, and social value and societal impact.