Computational Engineering for Nuclear Solvent Extraction Equipment

The ultimate objective of this work is to leverage modern computational tools to provide a unique and contemporary approach to pulse sieve-plate extraction column (PSEC) design and optimisation. Particular attention is given to providing novel analysis on: the functionality of operation, methods of performance analysis, determination of flooding, and development of simulation approaches that faithfully represent PSEC hydrodynamic behaviour.

A detailed assessment is undertaken of the dispersive mixing and turbulence characterisation of an industrially representative PSEC. This is achieved with computational fluid dynamics (CFD) running turbulence resolving large eddy simulation (LES), coupled with the volume of fluid (VOF) multiphase approach. Found was the dependency of PSEC functionality on turbulence production, and not on the viscous plate-induced stresses, generated therein. Consequently, the standard round-hole sieve-plate design is found to perform poorly at producing and distributing the types of flow and turbulence beneficial to droplet size reduction. This milestone discovery marks the first explicit contribution to knowledge of PSEC operation in decades.

Subsequently, a number of typical unsteady Reynolds averaged Navier-Stokes (URANS) turbulence modelling methods were compared against the benchmark LES. The URANS models, highly representative of the available PSEC CFD literature, were not able to produce agreeable solutions in the important hydrodynamic characteristics of the flows. Therefore the standard has been set for turbulence characterisation in PSEC simulation with LES.

The appropriate LES VOF method was carried forward to a campaign of 25 unique case runs that resulted in synergistically rich data set. Novel means of flooding identification was developed and tested. From this a number statistical analysis methodologies were employed to develop tools which successfully resolve the operational envelope and diagnose the likelihood of flooding during operation based on easily measurable variables.

Lastly, a state-of-the-art two-fluid hybrid VOF/Eulerian-Eulerian multiphase CFD model, with population balance, was implemented and interrogated. The model was successful in capturing all scales of the multiphase behaviour to further improve the faithful description of the complete fluid interactions. The population balance produced predictions for the droplet size distributions inline with available examples from literature and therefore provides exciting opportunities for accurate mass transfer predictions in pulse column simulations.