Core degradation analysis for a generic German PWR with the severe accident code ATHLET-CD

The progress of core degradation as well as evaluation of time spans for key events during the accident evolvement provides essential information related to the safety assessment of nuclear power plants. Knowledge is gained from performed experimental programmes which support the development of computer models incorporated in computer codes for analysis of severe accidents. Severe accident codes are applied since decades and constantly improved on the basis of gained new knowledge. Code-to-experiment comparison as well as code-to-code comparison is of paramount importance for the verification and validation of the codes.
For assessment of the core degradation progression in a generic German pressurized water reactor of type KONVOI a computer model based on the severe accident code ATHLET-CD was applied. The model was primarily developed within the frames of the joint research project WASA-BOSS (Weiterentwicklung und Anwendung von Severe Accident Codes – Bewertung und Optimierung von Störfallmaßnahmen) funded by the German Federal Ministry of Education and Research. The model was applied for simulation and analysis of accidents with core degradation from two main groups of accidents – station blackout and small-break loss-of-coolant-accident. For the current paper we have focused on analysis of core degradation during a hypothetical station blackout severe accident scenario. Analysed is the severe accident progression with failure of the safety barriers providing insights into the main phenomena which could arise in such an accident like core heat-up, cladding failure, release of fission products, hydrogen production, core degradation and reactor pressure vessel failure.
The analysis of the simulation results showed the applicability of the developed model for simulation of accidents with core degradation from the initiating event until failure of the reactor pressure vessel. The model was tested for simulations with varying the fuel burnup, with main focus on the release of the fission products from the core.