Experimental study on the jet flow impacting PWR containment internal structures and spray activation under a postulated BDBA

Within the OECD/NEA PANDA project (2021-2025), a dedicated experimental campaign (P1A1 series) was conducted to investigate large-scale containment thermal-hydraulics phenomena during Beyond Design Basis Accident (BDBA) scenarios. The experiments were characterized by steam and helium (used to simulate hydrogen) released inside a compartment representing a steam generator tower, followed by spray activation in the containment upper dome. The campaign assessed the effects of geometrical parameters in the steam generator tower model, such as side aperture sizes of 0.01 m 2 and 0.03 m 2 at the lower part of the tower and the presence of an impinging plate, as well as different spray configurations, including single versus multiple nozzles and spray water temperatures of 40 °C, 60 °C, and 80 °C. Instrumentation provided measurements of pressure, temperature, gas mixture composition, and velocity fields. The outcomes of the experiments revealed that the side aperture size of the compartment strongly influenced thermal stratification. In contrast, the impinging plate had a negligible effect outside the compartment. Spray activation effectively reduced the containment pressure, with faster depressurization achieved using a single nozzle due to higher injection momentum, while lower spray water temperatures enhanced steam condensation efficiency. The data provide insights into spray containment interactions and contribute to the development of a phenomenological database for the assessment and validation of advanced computational tools, such as GOTHIC and CFD codes, applied in containment safety analysis.