The ATHLET-CD (Core Degradation) code has been developed and validated for accidents resulting in major core damage. The development and integration of models in ATHLET-CD is done in close co-operation with the Institut für Kernenergetik und Energiesysteme (IKE), of the University of Stuttgart.

By the models for the formation and movement of metallic and ceramic melts in the core area and the thermal behavior of particle beds, as well as for the release of fission products and aerosols in the core area and their transport and deposition in the cooling circuit, the application range of the computer code has been extended significantly.

This is demonstrated by successful post calculations of bundle and integral experiments, such as CORA, QUENCH, LOFT-LP-FP2 and Phébus FP, or the TMI-2 accident and the incident at Paks-2 (NEA 2008). As demonstrated by the calculation performed for Phébus FPT1 within the framework of the International Standard Problem (ISP-46), full plant simulations can be performed with the version coupled with COCOSYS.

The ATHLET-CD structure is modular, both to provide a variety of models for the simulation and to provide an optimum basis for further development. For a comprehensive simulation of the thermal-fluid dynamics in the nuclear steam supply system, the ATHLET system code has fully been integrated.