Influence of surface wettability increase induced by Gamma-ray irradiation on critical heat flux in downward-facing flow boiling

•Surface wettability of the metal can be increased by Gamma-ray irradiation.•Surface wettability increase will lead to decrease in the active nucleation site.•CHF is not enhanced even though the surface wettability increases a lot.•CHF results are analyzed considering characteristic of downward-facing flow boiling.