Statistical characterization of the interfacial behavior captured by a novel image processing algorithm during the gas/liquid counter-current two-phase flow in a 1/3 scaled down of PWR hot leg

•The liquid hold-up fluctuations of gas-liquid counter-current flow in PWR hot leg was analyzed statistically.•The data were analyzed using non-linier statistics, discrete wavelet transforms, and the Kolmogorov entropy.•There were no significant differences between the flooding mechanisms for both air/water and steam/water flows.•The higher the system pressure, the higher the frequency occurrence of slugging during flooding.•Kolmogorov entropy enables to correlate the stabilizing effect due to the fluid resistance during flooding.