Experimental study on gas entrainment at free surface in reactor vessel of a compact sodium-cooled fast reactor

Kimura, Nobuyuki; Ezure, Toshiki ; Tobita, Akira; Kamide, Hideki 

An innovative sodium cooled fast reactor has been investigated in a frame work of the fast reactor cycle technology development project. A compact reactor vessel (R/V) is designed to reduce the construction cost. One of the thermal hydraulic issues in this design is gas entrainment at a free surface in the R/V. A water experiment was performed using a partial model with 1/1.8th scale. The objective is to investigate occurrence conditions and the mechanism of the gas entrainment. It was found that there were two kinds of the gas entrainment phenomena and the occurrence conditions were far from the reactor condition. One type of the gas entrainments occurred at the wake region of the cold leg pipe due to larger horizontal velocity. Other one broke out at the region between the hot leg pipe and the R/V wall when the coolant level was low and the downward velocity was large.