Dry-out and rewetting phenomenon may occur on a fuel rod surface during anticipated operational occurrences (AOOs) for a boiling water reactor (BWR). The conventional rewetting model included in the current system code tends to underestimate the rewetting propagation velocity due to the absence of an appropriate precursory cooling model. The present research aims at the development of a mechanistic model for the precursory cooling in the annular mist flow regime typical of AOO and anticipated transition without scrum (ATWS). Rewetting experiments were carried out using a single heater rod in the circular glass pipe with air-water flow at atmospheric pressure to visualize the rewetting behavior and obtain mechanistic understanding on the phenomena. This paper summarizes the experimental results and discusses the liquid film flow characteristics including roll wave formation and spattering at the rewetting front.

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