During a hypothetical severe accident in a pressurized water reactor (PWR) of nuclear power plant, hydrogen would be generated during the degradation of the reactor core. The ignition and ensuing combustion of hydrogen could cause a sharp pressure increase, which could threaten the integrity of the containment.

The present work describes the execution and results of the Upward Flame Propagation Experiment (UFPE) on hydrogen combustion within the EC LACOMECO project. Two experiments were performed at the HYKA A2 experimental facility (KIT), which is a cylindrical vessel of 220 m3 free volume, 9.1 m height and 6.0 m internal diameter. A homogeneous mixture of hydrogen (11–12 vol.%), steam (20–21 vol.%) and air was established in the vessel. The initial pressure was 1.5 bar, and the average initial temperature was about 90.0 °C. The mixture was ignited at the bottom of the vessel and the ensuing axial and radial flame propagation were observed. Pressure, temperature and flame velocity were measured at different axial and radial locations. The flame propagation was recorded by a high speed video combined with a Background Oriented Schlieren (BOS) method. The experimental results were finally compared to the results of the well-known THAI HD-22 experiment, which was performed at almost similar conditions.

The objective of current work was to investigate the effect of scale on flame propagation regime in order to clarify how can phenomena observed in a scaled-down experimental facility be extrapolated to an actual containment scale. Another goal was to provide detailed experimental data for numerical code validations in a large scale.

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