Solvent extraction processes have proven to be very efficient in the task of removing the long-lived radiotoxic nuclides from spent nuclear fuel. New separation systems are constantly developed and demonstrated in lab-scale process tests. The process optimisation and modelling is an important part of this work and for this purpose the SX Process software has been developed. The software is focused on lab-scale processes in miniature centrifugal contactors which are fully designed through the software interface, meaning that no change in the code is necessary for a new system. A relatively simple model has been developed and implemented to calculate the transfer between the phases in centrifugal contactors. With this model the americium profile from a previous SANEX process run could be calculated with good accuracy. (C) 2013 Elsevier Ltd. All rights reserved.