Study to clarify mechanism behind heat transfer enhancement in reactor due to RISA

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The final goal of this study is to clarify the mechanism behind enhancements of wall surface wettability and boiling heat transfer due to the radiation induced surface activation (RISA) under high-temperature and high-pressure conditions equivalent to thermal environment in a core of light water reactor. Detailed discussions about dynamic wettability at ambient temperatures up to 250 degrees centigrade were made based on the experimental data. The results showed that the advancing contact angles were decreased due to gamma-ray irradiation at all conditions tested and revealed that the dynamic wettability was enhanced due to the RISA even under high-temperature and high-pressure conditions.In order to evaluate the effect of surface wettability on liquid film dryout in annular-mist flow, the flow characteristics of liquid film and droplets near the condition in which the liquid film dryout occurs were also observed in detail using two-test pipes with different surface wettability.