Safety analysis codes for nuclear reactors utilize the minimum film boiling temperature as a decision parameter whether or not the fuel cladding is wetted by the coolant during the reflooding process. In spite of its importance, however, previous correlations for the minimum film boiling temperature have been based mostly on pool boiling or not-low pressure flow boiling. In general, reflooding proceeds at a low flow rate (～cm/s) under a low pressure (～bar). Thus, it is not reasonable to directly apply existing correlations to predict the quenching temperature for bottom reflooding. This study is devoted to measure the minimum film boiling temperature for vertical flow boiling at low pressures and mass fluxes. A hot-patch technique was used to form a stable vapor film in a vertical tube. In this study, the quenching temperature is the minimum film boiling temperature at which a vapor film collapses spontaneously.
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