Dryout of water film on a heated tube surface caused by an obstruction in a boiling two-phase vertical upward flow (1st report, observation of flow pattern and dryout generation in annular channel)

Both economy and safety of the nuclear power stations are strongly demanded. One of the problems in the thermal design of a nuclear reactor, especially in BWR, arises near the spacer supporting the nuclear fuel rods. The purpose of the present paper is to make clear the mechanism causing the water film breakdown which results in the burnout of heating tube near the spacer, and its relation to the flow pattern. The experimental results show that film breakdown occurs near the leading edge, i.e., just below the spacer, as well as the inside of the down part of the gap between the outer surface of the heating tube and the simulated spacer.