Experimental Study of Counter Current Flow Limitation for Water and Air Injection in Cold Conditions Inside a Semi-Spherical Narrow Channel

The International Nuclear and Radiological Event Scale (INES) determined that the Three Mile Island Unit 2 (TMI-2) severe accident is at the fifth level. The damage caused the core reactor to melt and formed debris collected at the bottom of the RPV. However, the Reactor Pressure Vessel (RPV) integrity was still maintained because of the heat transfer phenomenon. The boiling heat transfer has different characteristics based on the gap size. At gap sizes below 2 mm, the heat transfer is influenced by Counter Current Flow Limitation (CCFL). Based on the previous explanation, this study aims to observe the phenomenon of CCFL in a semi-spherical geometry to illustrate the lower plenum RPV. The test section is semi-spherical and made from stainless steel 316 with a 300 mm diameter. It is covered with a 340 mm diameter of quartz glass bel-jar adjusted with a 2 mm gap, and the working fluid is water injected by air with three different levels. The experimental data in liquid and gas superficial velocities will be processed to obtain the CCFL correlation and predicted with the correlations from several researchers. The experimental result showed that the liquid and gas superficial velocities are directly proportional to the level of air injection and impact the slope and constant of the CCFL correlation. From the data prediction with the CCFL correlations from the other researchers, it can be known that the CCFL in semi-spherical test geometry is quite similar to the other geometry.