Hydraulic experiment for compact reactor vessel; Measurement of flow field and flow optimization in upper plenum

Kimura, Nobuyuki; Hayashi, Kenji; Ito, Masami*; Sekine, Tadashi*; Igarashi, Minoru; Sato, Hiroyuki; Kamide, Hideki 

An innovative sodium cooled fast reactor has been investigated on the FBR feasibility study. The design of the reactor is undergoing in order to reduce the construction cost of the reactor. For example, thermal output is increased against the reactor size and an upper inner structure (UIS) has a slit for the arm of the fuel-handling machine to simplify the fuel exchanging system. The dipped plates (D/P) are set below the free surface to prevent gas entrainment at free surface. 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 upper plenum, all of main components were set up as well as the reactor design. In addition, the D/P has a hole in front of the slit of the UIS to insert the fuel handling machine(FHM). As the experimental parameters, the core outlet velocity was varied from the condition of the Froude number similarity to the same value as the real reactor. The local velocity was measured by the particle image velocimetry and the ultrasound Doppler velocimetry. In the experimental results, gas entrainment at the free surface was not observed in the range from the Froude number similarity condition to the same velocity condition as the real reactor. However, the free surface was bulged on a large scale in front of the UIS slit. At the neighborhood of the H/L intake, three vortex cavitations were observed. The vortex cavitations were broken out under the same cavitation coefficient condition based on the H/L velocity as that in the real reactor. A vertical rib was set on the reactor vessel wall near the H/L inlet to restrict the rotating flow at the neighborhood of the H/L. As the result, the vortex cavitation at the region between the reactor vessel wall and the H/L was supressed under the same cavitation factor condition as the real reactor. A vertical cylinder, named FHM plug, was installed to close the hole in the D/P fbr FHM.