CFD Simulation of the Flow Inversion in a Uniformly Heated Rectangular Channel Array

A CFD simulation using the ANSYS-CFX code was conducted on the flow inversion in a thin rectangular channel array mimicking a plate type fuel assembly, which was modeled using an in-line array of 21 thin plates generating heat uniformly. The 21 plates make 22 thin rectangular channels. The upper part of the thin channels is connected to a large space representing a reactor pool. The lower part of the thin channels is extended to an outlet connected to a large space through a flap valve. The CFD model can take account of a pump coast down, decay power at the plates, and the flap valve opening in research reactors. Two buoyancy models were examined to find out the effect and select a more suitable one for this simulation. The CFD simulations were conducted for 80 seconds after the reactor shutdown in order to see the flow behaviors through the flap valve as well as the flow inversion in the channel array. A numerical simulation using the RELAP5 code was also conducted to be compared with the simulation results of CFD. (author)