The Generation IV International Forum promotes six advanced nuclear systems which could improve the fuel cycle sustainability. Two of these are the Sodium Fast Reactor and the Molten Salt Reactor, fast-spectrum designs which could be operated in batches and converge to an equilibrium state. The equilibrium fuel cycle is a useful reference to evaluate and compare the neutronic performances of different systems. The goal of this work is to contribute to model the equilibrium fuel cycle of the two Generation-IV systems mentioned above with focus on the development of efficient fast-running tools. Both of the systems are simulated in an open cycle with fixed fresh fuel composition and batch-wise refuelling. The applications of this work concern the evaluation of a radially infinite Serpent model of the European Sodium Fast Reactor (ESFR) and a parametric study aimed at reducing the dimensions of a Breed and Burn Molten Salt Reactor (MSR). The tool employed and extended is a Python based script, called Batch Burnup Procedure, applicable to both solid and liquid fuel systems. This routine calls the Monte Carlo code Serpent2 for burnup and transport simulations, and can automatize batch-wise refuelling by manipulating Serpent input and output files until equilibrium is reached. The reduced infinite ESFR model can reproduce precisely some features of the ESFR inner fuel region. To produce fine safety feedbacks maps of the core, however, extremely high statistics must be implemented to overcome the strong stochastic noise. In this work, Breed and Burn batch-wise operation was proven to be feasible for a U-Pu Chloride fuelled MSR if non-soluble fission products removal is adopted. The core dimensions were largely reduced by implementing a multi-fluid layout.