Investigating sedimentation process in the plutonium reconversion using Eulerian Two-Fluid simulations and experimental verification

Abstract

Batch settling simulations were used to investigate the sedimentation behaviour of cerium oxalate particles (surrogate to plutonium) in the nitric-oxalic acid solution which will be useful for the design of continuous process equipment used in plutonium reconversion. The effects of overall solid fractions (OSF), initial dispersion height (ht), and cylinder diameter (d) on the settling curve were investigated numerically and comparisons were made with experimentally obtained results. Further, the solid volume fraction distributions of cerium oxalate obtained by varying the dispersion height, OSF, and cylinder diameter were numerically analysed. The increase in OSF (dispersed phase concentration) led to the presence of high solid volume fraction inside the settler. Since, the dispersed phase volume fraction is more and closely packed, it experiences the delay in settling time. The analysis of pressure variation was done by varying ht, d, and OSF. The bulk settling velocity was computed for different OSF and ht values. It was observed that the settling velocity was reduced with an increase in OSF and was independent of d. The changes in bulk settling velocity with time helped to explain the separation process in detail. The vorticity and velocity fluctuations obtained along the height of the batch settler confirmed the random motion of solid phase during settling. The clear liquid separated at the top region of the batch cylinder was investigated as a function of sedimentation velocity which will be helpful for any future design optimization of a continuous separation equipment.