International standard problem on containment thermal–hydraulics ISP47: Step 1—Results from the MISTRA exercise

The understanding of hydrogen distribution during severe accidents in a nuclear reactor containment is still an open issue. Several containment thermal–hydraulics international standard problems (ISP) have been conducted to address this topic. However, the predictions made by the available lumped parameter or CFD computer codes were generally not satisfactory. Therefore, a new exercise was launched in 1999 using new state-of-the-art experimental facilities TOSQAN, MISTRA and ThAI that included sophisticated 3D instrumentation and well-controlled boundary conditions. Predictive capabilities of important and still uncertain phenomena such as wall condensation, natural circulation and gas stratification are assessed. In addition, comparison between lumped parameter (LP) and CFD codes and assessment of the capability of CFD codes to deal with scaling effects are performed. This article reports on the part of the exercise which concerns the MISTRA facility including experimental results and blind benchmark exercises.