COMPARISON OF POINT KINETICS, IMPROVED QUASISTATIC AND THETA METHOD AS SPACE-TIME KINETICS SOLVERS IN DONJON-3 SIMULATIONS

摘要

To ensure the safety of nuclear reactors, we have to simulate accurately their normal operation and also accident cases. To perform transient calculations, coupled neutronic and thermohydaulic codes are used. This article compares three neutronic solvers. The first one is the point kinetic approach where the flux shape is constant during all the transient. For the second method (the improved quasistatic method), the flux shape is constant but only during small time steps. Finally, we used the theta approach where both flux and precursors distributions vary with time and space. Transients of Lost Of Coolant Accident in CANDU-6 reactors have been simulated with DONJON and the outputs of a thermalhydraulic system code. Results show that the point kinetics is inappropriate for transient with large distortion of the flux shape. Improved quasistatic and theta methods give relatively similar results. However, the improved quasistatic approach is less stable and a little bit more sensitive on time-step and spatial discretization than the theta method is.