Thermal hydraulic modelling of grating effect for application to 3-dimensional analysis of hydrogen behavior in NPP containment

Abstract

For three-dimensional analysis of the thermal hydraulic phenomena associated with hydrogen behavior in a containment building, geometry modelling that reflects the three-dimensional features of the containment building is required. A lot of equipment and concrete structures are installed in the containment building, and gratings are also installed on a large floor area. Gratings in the containment can affect gas flow and heat transfer, so modelling of the grating is required for three-dimensional analysis of hydrogen behavior in the containment. As a method of modelling gratings, many computational mesh nodes are required to directly simulate gratings made of steel plates several millimeters thick, so a large amount of computation is required for accident analysis. Therefore, simple modelling of gratings is required to properly control the size of the three-dimensional mesh. In this study, a method of simulating porous media for gratings was adopted, and the model was extended to allow for consideration of heat transfer of the gratings. To verify the porosity-based grating model, analyses of the H2P1_10_2 experiment recently performed through the international joint project OECD/NEA HYMERES-2 were conducted. Through a comparison with the H2P1_10_2 experimental data, it was confirmed that the porous media-based model showed calculation results very similar to those of the direct simulation of the grating, and that the porous media-based model reduced the mesh size by 1/5 and the calculation time by 1/5 compared to those values in the direct simulation of the grating.