Comparisons between multidimensional and lumped-parameter gothic containment analyses with data

Advanced nuclear reactor concepts heavily rely on the availability and effi ciency of passive cooling systems. This especially holds for advanced conta inment designs with passive decay heat removal systems that function by nat ural phenomena. Also, the development of catalyst modules for hydrogen miti gation measures is based on natural basic principles leading to hydrogen re duction and additional atmospheric mixing. To prove the functionability and availability of passive systems and their respective components, demonstration experiments at different scales are ma ndatory. In addition, it is the general perception that many more improved computational tools are needed for this purpose, where present lumped-param eter analysis methods are insufficient to provide the necessary information about local details and spatial distributions. Therefore, the next step in the development of analytical/numerical models is the transition/extension from lumped-parameter to multidimensional models and containment analysis codes. Also, recent posttest lumped-parameter analyses of the Heiss Dampf Reaktor H-2, distribution experiment E11.2 with preexisting atmospheric stratificat ion show a number of deficiencies compared with the data, indicating a need for more detailed modeling. The GOTHIC thermal-hydraulic containment code provides this required extens ion of the lumped-parameter model by incorporating multidimensional submode ls for selected nodes (subcompartments). Applications of both model types t o simulate hydrogen dispersion experiments in the Battelle Model Containmen t (BMC) demonstrate the limitations of the traditional approach and the imp rovement achieved by the multidimensional simulation. The importance of the rmal and hydrogen concentration stratifications, the interactions with stru ctural heat conductors, and the requirements to set up a consistent model w hen coupling lumped-parameter and multidimensional representations are disc ussed. Several hydrogen-mixing experiments performed in the BMC more than a decade ago were simulated with multidimensional GOTHIC models. Three types of modeling concepts have been tested: 1. lumped-parameter model 2. each compartment modeled two-dimensionally with the intercompartment con nections simulated as flow path junctions 3. full three-dimensional nodalization of the BMC, intercompartment connect ions simulated as gaps. The results of these GOTHIC calculations are compared with the experimental data and demonstrate the improvements that can be achieved by performing m ultidimensional containment simulations.