New kinetic simulation capabilities for Tripoli-4®: Methods and applications

Thanks to the growing computer power, it is now feasible to apply Monte Carlo methods to the solution of non-stationary transport problems in reactor physics and in criticality-safety, which play an instrumental role in producing reference numerical solutions for the analysis of transients occurring during normal and accidental behaviour. In this respect, a major scientific challenge is represented by the very different time scales of neutrons and precursors, which demand distinct strategies and variance reduction techniques with respect to stationary simulations. In this work we will present the principal algorithms and simulation methods that have been explored and selected for the kinetic capabilities of Tripoli-4®, the production Monte Carlo code developed at CEA. The efficiency of the tested methods will be demonstrated on simple geometries as well as on step reactivity insertion and extraction due to control rod movements for the experimental reactor SPERT-III E-core. The solutions obtained by using Tripoli-4® will be compared to the point-kinetics approximation and to the asymptotic analysis based on alpha eigenvalues.