Evaluation on gas entrainment in reactor vessel using 1/1.8th scaled model; Investigation on dominant factors based on occurrence map and mechanism for gas entrainment

Kimura, Nobuyuki; Ezure, Toshiki ; Tobita, Akira; Ito, Masami*; Kamide, Hideki 

For an innovative sodium cooled fast reactor, a compact reactor vessel is designed to reduce the construction cost, where sodium flow velocity increases. One of the thermal hydraulic issues in this design is gas entrainment (GE) at free surface in the reactor vessel (R/V). Dipped plates (D/P) are set below the free surface in order to prevent the GE. To evaluate GE, we made the partial apparatus modeled the 90 degree sector of the R/V with a central focus on the hot leg (H/L) pipe circumferentially and region above the D/Ps vertically. We obtained an occurrence map of the GE in order to evaluate the dominant factor for the GE. In the map, it was found that there were two kinds of the GE phenomena. One of the GE occurred at the downstream region of the cold leg pipe. Other one broke out at the region between the H/L pipe and the R/V wall. The mechanisms of the GE at the two regions were clarified by applying the PIV.