Numerical Analysis of Solid–Liquid Disengagement in a Continuous Precipitator Relevant to Plutonium Reconversion

The spent fuel reprocessing under PUREX process that separates Pu and U from fission products is widely used to generate additional amount of energy from nuclear reactors. The plutonium nitrate solution obtained from solvent extraction is converted to plutonium oxide powder through reconversion for the deployment of plutonium-based fuels in the reactor. Plutonium is precipitated as plutonium (IV) oxalate from the nitrate solution using oxalic acid in batch or semi-continuous precipitator, followed by filtration and calcination to obtain plutonium oxide powder. The understanding of precipitation behaviour of plutonium oxalate particles in oxalic + nitric acid medium is essential for the design of continuous precipitator/thickener to increase the throughput and minimize human exposure. Cerium as surrogate to plutonium is often used under harmless conditions for equipment design and process development. In this work, Euler-Euler simulations of solid–liquid disengagement were performed to investigate the detailed hydrodynamic inside a continuous precipitator by varying different parameters such as impeller speed, solid concentration and height of overflow outlets. The predictions through computational fluid dynamics (CFD) simulations is utmost important for the design of continuous precipitator/thickener in Pu reconversion. The developed CFD model will be useful to simulate the cases which are experimentally not feasible.