One of the critical issues in the development of Breeding Blankets for the Fusion Demonstration Reactor, DEMO, is the tritium control, particularly in the coolant and the tritium extraction system. To be able to understand and model the tritium behaviour and releases through various interfaces, a code is being developed, following the same approach as for Liquid Metal Fast Breeder Reactors (LMFBRs) for which an efficient tool is already available: KUTIM, here described The new model proposed for fusion purposes will contribute to compare and choose means to reduce the tritium releases and more generally will be a support for design activities for Breeding Blankets.