Simulation of subcooled flow instability for high flux research reactors with ATHLET

The ATHLET code has been improved and validated for the safety analysis of high flux research reactors against experimental data of the Thermalhydraulic Test Loop of Oak Ridge National Laboratory (ORNL). Therefore, an extensive series of "stiff mode" experiments were recalculated. The comparison between experiments and ATHLET posttest calculations shows that the extended code simulates accurately the thermalhydraulic conditions and the flow instabilities in a wide range of inlet velocity, head and mass flux.