Simulation of a Severe Accident in a German Generic PWR with the Code System AC2

Safety analysis is a crucial part of nuclear safety, both for the licensing and the design assessment of new, as well as for existing nuclear power plants. Particular interest has been drawn to severe accident analyses after the accident in Fukushima. Key points of the analyses are the time required to reach core degradation, the extent of the degradation and the release and transport of radioactive material first into the containment, later possibly to the environment. Another main interest of the analyses is to assess the possible counter measures preventing core degradation and eventually the radioactive release. The simulation environment AC(2) contains the thermal hydraulic system codes ATHLET, ATHLET-CD (severe accident module) alongside with the containment code COCOSYS and the interactive analyses simulator ATLAS. It is being developed by GRS (Gesellschaft fur Anlagen- und Reaktorsicherheit gGmbH) for the analysis of the whole spectrum of operational transients, design-basis accidents and beyond design-basis accidents anticipated for nuclear energy facilities. The main advantage of this code system assembly is its capability to simulate severe accidents as a whole, starting from the normal operation throughout the core degradation phase, and finally the assessment of the containment behavior, enabling the user to determine the source term released to the environment. Present study focuses on a severe accident scenario in a German generic PWR. The simulated scenario is a medium break cold leg LOCA during a station blackout. The aim of the study has been to assess the extent of core degradation and radioactive release into the containment. The calculations have been performed with the code system AC(2).