Penalization of zero-dimensional containment pressure calculations by comparison with three-dimensional models

Sammanfattning

Modeling the pressure in the containment building of a Pressurized Water Reactor following a Loss Of Coolant Accident is a critical topic, especially in the medium and long term, where experimental data is scarce. This document aims at comparing results obtained with 0D and 3D GOTHIC calculations, to ensure 0D predictions used in safety analyses remain conservative. Because manually generating 3D models in GOTHIC is highly time-consuming and error-prone, the development of an automated tool to generate 3D models – the VOXELS method – had begun before this present work. Throughout this work, methodological enhancements were integrated into this tool to enable the automated generation of reliable 3D simulations. A method allowing to lump thermal conductors together and to span them locally was then chained to the VOXELS approach. The comparisons finally performed between results obtained with 0D and 3D calculations show that the long-term pressure tends to be underestimated by 0D analyses. This mainly results from an excessively high prediction of heat absorption of thermal conductors located in the lower floors in the 0D analyses. Hence, it is proposed to remove thermal conductors located below a certain height of the containment building. This corrects the underestimation of the pressure and ensures that 0D analyses remain conservative.