Thermal hydraulic phenomena play a decisive role for the course of sev
ere accidents in light water reactors. Therefore, the simulation of th
ese accidents with computer codes requires comprehensive and detailed
modelling of these processes. The cone ATHLET-CD is being developed fo
r realistic simulation of accidents with cole degradation and for eval
uation of accident management measures. It makes use of the detailed a
nd validated models of the thermal hydraulic code ATHLET in efficient
coupling with models for core melting and fission product behavior The
capabilities of the coupled code are demonstrated by a calculation of
the TMI-2 accident.