Oxalic precipitation is usually applied to process radioactive wastes or to recover actinides from a multicomponent solution. Due to their later handling and use, actinide precipitates have to satisfy strict requirements. In nuclear environment where experiments are limited, simulation may be the only way to test different industrial configurations in order to adjust industrial campaigns. In this manuscript, the modelling of the tetravalent uranium oxalate precipitation in an unbaffled reactor is achieved using a hybrid multizonal/CFD model. The population balance is solved according to the moment method in a multizonal model entirely parameterised through computational fluid dynamics calculations based on large-eddy simulation (LES) and a sub-grid model of micromixing. The modelling is applied to show how the specificity of flow field in an unbaffled reactor can have a noticeable effect on the uranium oxalate properties. (C) 2012 Elsevier Ltd. All rights reserved.