(GRS-670) Further Development of the Module ATHLET-CD of the Code Package AC²

L. Lovasz, L. Tiborcz, P. Pandazis, C. D’Alessandro, Y. Périn, T. Hollands, K. W. Wong, A. Wielenberg

Research Project RS1574

As part of the reactor safety research funded by the German government, the ATHLET-CD computer code system is being developed for safety analyses of nuclear power plants with pressurised and boiling water reactors and for the evaluation of plantinternal emergency protection measures. The objective is to provide a largely mechanistic analysis tool for a realistic simulation of severe accidents in water-cooled nuclear reactors. Furthermore, the performance of the code system should allow realistic analyses of beyond-design-basis accidents as well as the simulation of advanced core destruction with an extended model scope to be carried out in reasonable computing time.

ATHLET-CD is based on the ATHLET thermal-hydraulic models. On the basis of the ATHLET models, it is possible to derive the initial and boundary conditions for the calculation of accidents with ATHLET-CD directly from previous transients. The current version of ATHLET is fully integrated in ATHLET-CD. ATHLET-CD contains modules for the simulation of fuel rod and control element destruction in pressurised and boiling water reactors, models for the description of phenomena in the lower plenum, as well as modules for the release and transport of fission products and aerosols in the cooling circuit, including the decay of nuclide inventories and chemical reactions in the gas phase. Within the framework of project RS1574, models were further developed or newly implemented in the following subject areas and the following quality assurance measures were carried out:

− Core destruction and relocation of the core meltdown
− Fission product transport
− Phenomena in the lower plenum and simulation of ex-vessel cooling
− Extension of the documentation, improvement of the user-friendliness
− Extension and automation of the test base
− Customer support and bug fixes

With this work, the quality of the recalculations of transients, accidents and accident sequences in nuclear reactors and of tests could be significantly increased. In addition, the overall robustness of ATHLET-CD could be improved.