1-3 Smooth and Calm Flow in a Compact Reactor Vessel

- Flow Optimization in a Compact Sodium Cooled Reactor -

Fig.1-6 Schematic of reactor vessel of sodium cooled reactor

 

Fig.1-6 Schematic of reactor vessel of sodium cooled reactor

 

Fig.1-7 Velocity measurement and effect of FHM Plug in 1/10 scaled model

Fig.1-7 Velocity measurement and effect of FHM Plug in 1/10 scaled model

Flow velocity field was measured in the 1/10 scaled water test model of the reactor vessel. The FHM plug at middle height could change the flow direction and reduce the velocity near the free surface. Particle Image velocimetry was applied to get the detailed flow velocity fields.

Fig.1-8 Visualization of gas entrainment and example of numerical analyses

Fig.1-8 Visualization of gas entrainment and example of numerical analyses


Development of advanced technology for a sodium cooled reactor has been carried out as a part of the fast breeder reactor (FBR) feasibility study. A compact, high power system as shown in Fig.1-6 is planned to reduce construction cost. The Upper Inner Structure (UIS) has a slit where an arm of Fuel Handling Machine (FHM) can go inside so as to reduce the diameter of the reactor vessel (RV). Further, sodium can flow through the UIS.

Because of these design features, the sodium exiting from the core flowed upward with high velocity through the UIS slit. As a result, flow velocity near the free surface in the RV was increased. This may results in gas entrainment (GE) at the free surface. Dipped plates were set below the free surface to reduce the flow velocity near the surface. However, prevention of the GE is still a significant issue in the design.

A flow optimization study based on experiments and numerical analyses has been performed. An FHM plug was invented to shut the high velocity flow toward the free surface based on the velocity calculation shown in Fig.1-7. Velocity near the free surface was reduced by half.1) Further, numerical analyses as shown in Fig.1-8 were applied to the GE phenomena and an estimation method of the GE was developed.2) The prospect of preventing GE in the reactor was obtained by these studies.


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