FITXS: A fast and flexible burn-up scheme based on the fitting of one-group cross-sections

The closure of the nuclear fuel cycle is currently envisaged with the deployment of Generation IV fast reactors which are able to generate their fuel from fertile 238U or 232Th, and also burn minor actinides arising from legacy wastes and thermal reactors in the nuclear park. The optimization of such fuel cycle strategies requires detailed models, capable of simulating the transition from initial state to equilibrium. Due to the high computational cost of detailed burn-up calculations, most scenario codes use parametrized few group cross-sections to calculate fuel depletion in the reactors. This paper presents a fast and flexible burn-up scheme called FITXS which we applied on the GFR2400 Gas-cooled Fast Reactor and a European Pressurized Reactor MOX fuel assembly. Based on the fitting of one-group cross-sections as functions of the detailed fuel composition, the developed models are able to calculate spent fuel compositions with high accuracy for a wide range of initial compositions in less than one second computational time. In order to demonstrate applicability, the models were integrated into a fuel cycle model containing GFR2400 and European Pressurized Reactors, as well as conventional Light Water Reactors, and the fuel utilization and transmutational properties of the system were analyzed. It was found that the GFR2400 can operate in a closed fuel cycle, with positive breeding gain in the equilibrium. Increased minor actinide feed improves breeding in the GFR2400, but the accumulation of plutonium can be prevented by recycling the excess plutonium as MOX fuel in thermal reactors.