Hydraulic Experiment on Flow Optimization in Compact Reactor Vessel; Effects of double dipped plates and outer shell of UIS

Nakayama, Oukatsu; Kimura, Nobuyuki; Kamide, Hideki ; Ito, Masami*; Sekine, Tadashi*

On the FBR feasibility study, an innovative sodium cooled fast reactor has been investigated in Japan Nuclear Cycle Development Institute. In order to reduce the construction cost of reactor, the compact reactor vessel is designed. Gas entrainment at the free surface is one of issues to be solved because of high velocity in the upper plenum vessel. We performed an 1/10th scaled model water experiment for the upper plenum of reactor vessel and investigated flow fields in the plenum in order to optimize flow. In the last experiment, we established flow optimization structures for reduction of flow toward to the free surface and restraint on the vortex cavitations near H/L inlet, i.e., plug into the dipped plate hole to install a fuel handling mechanism (FHM) and a flow splitter at vessel wall. In this report, effects of double dipped plates (D/Ps) and outer shell of upper inner structure (UIS) are investigated. In the result, we could confirm that the double D/P structure set below the free surface is effective to reduce flow toward the free surface between reactor vessel wall and guide tube of fuel transfer machine. An FHM plug, which has a step structure at mid height between double D/Ps, showed that it reduced flow velocity through the gap between the plug and the D/P. A perforated outer shell was set around the UIS to reduce vortex strength developed from the cold legs to the hot leg intake and also to restrain the vortex cavitation. It was shown that the onset condition of vortex cavitation at reactor vessel wall was reduced and the cavitation occurred easily. At the cold leg the onset condition of the caviation was not advanced. The flow distribution through the perforated outer shell should be optimized.