A dynamic model of a plutonium oxalate precipitator has been developed to provide a means of predicting plutonium inventory on a continuous basis. The model is based on state-of-the-art crystallization equations, which describe nucleation and growth phenomena. The model parameters have been obtained through the use of batch experimental data. For any time-dependent input concentrations and flow rates, the model permits one to calculate the output flow rate of the precipitate phase, the output concentration and flow rate of the filtrate phase, the degree of conversion, and the average particle size. The model has been used to study the approach to steady state, to investigate the response to input transients, and to simulate the control of the precipitation process.