[en] A computer program (CIXZE) has been developed to model Zeolon 900 ion exchange processes for study of the significant process variables. The program models the load, scrub, and elution cycle with four cations: cesium, sodium, potassium, and rubidium. Zeolon 900 equilibrium data is used in predicting the load, empirical data is taken into account in the scrub and elution models. The program has been tested and adjusted with B Plant Cesium Purification process data. During the period of most stable operation in 1975, the relation between the loading variables was accurately predicted. The scrub indicated realistic changes during a sensitivity study. Many of the process measurements had to be extrapolated to obtain the desired data due to the high ¹³⁷Cs concentrations in the system limiting the reliability of process sampling. The program was also tested with the proposed B Plant CAW process flowsheet. A critical judgment at this time is the loading capacity of the large Zeolon 900 column (T-18-2) in the flowsheet. Unfortunately data on the loading of Zeolon 900 with other cations (in the CAW feed) is not available at this time. Program results were helpful in the flowsheet design, however, optimization of the program with the CAW ion exchange process will be completed in conjunction with the pilot plant demonstration