Experimental study on flow optimization in upper plenum of reactor vessel for a compact sodium-cooled fast reactor

Kimura, Nobuyuki; Hayashi, Kenji; Kamide, Hideki ; Ito, Masami*; Sekine, Tadashi*

An innovative sodium cooled fast reactor has been investigated on the feasibility study of FBR cycle system in Japan. A compact reactor vessel (R/V) and a column type upper inner structure (UIS) with a radial slit for an arm of a fuel-handling machine (FHM) are adopted. Dipped plates (D/P) are set in the R/V below the free surface to prevent gas entrainment. We performed an 1/10th scaled model water experiment for the upper plenum of the R/V. Gas entrainment was not observed in the experiment under the same velocity condition as the reactor. Three vortex cavitations were observed near the hot leg (H/L) inlet. A vertical rib on the R/V wall was found inlet to restrict the rotating flow near the H/L. The vortex cavitation between the R/V wall and the H/L was suppressed by the rib under the same cavitation factor condition as in the reactor. The cylindrical plug was installed through the hole in the D/P for FHM to reduce the flow toward the free surface. It was effective when the plug was submerged into the middle height in the upper plenum. This combination of two components had a possibility to optimize the flow in the compact R/V.