Numerical Simulation Of Helium Flow And Fuel Pellets Cooling In High Temperature Gas Cooled Reactor

High temperature gas cooled reactor is the fourth generation of nuclear reactors, which is internationally recognized with good security. It is expected to become the first commercial demonstration nuclear power plants with modular high-temperature gas-cooled reactor that the plant located on Shidao bay will be completed in 2017. The process of flow and heat transfer between helium and fuel spheres was modeled and simulated in this paper so as to predict the distribution of temperature, velocity and pressure in the high temperature gas cooled reactor. The model of pebble bed filled with simple body centered cubic and body centered cubic arranged fuel spheres was set up by means of CFD numerical simulation, in which fuel spheres was modeled in real sizes and with real heating zone. The physical properties of helium gas are variables related to temperature and pressure. Structural mesh was generated by use of ICEMCFD. Two and a half and two fuel spheres were separated modeled as representative unit of the simple body centered cubic pebble bed. For example, the case of the 3rd fuel sphere and an analysis of temperature field were conducted. Also, the helium velocity and pressure fields were extracted and then analyzed. Seven one-eighth fuel spheres were modeled as representative unit of body centered cubic arrangement pebble bed. For example, the case of the 5th fuel sphere and an analysis of temperature field were conducted. Also, the velocity field and pressure field data of helium gas was extracted and then analyzed. Consequently, the PROFILE boundary files in FLUENT code was used to carry out superposition calculation on simple body centered cubic ball bed and body centered cubic pebble bed model.The simulation result shows that: there was whirlpool of helium gas whose flow included mainstream zone and refluxed zone after each fuel sphere. The highest temperature of the fuel sphere is at the upper portion of the center of the sphere and decreases with the increasing radius. The temperature near the tangent point of fuel spheres is lower than that near the main channel region of helium gas. The temperature of the upper hemisphere is higher than that of the lower hemisphere. The pressure of helium gas had a wave-like decrease with the changed size of the gap between the fuel spheres. For the superimposed calculation of the simple body-centered cubic pebble bed, the rising rate of temperature is 19.95 K/m, the rise rate of the average temperature of helium gas is 19.93 K/m, the average drop of pressure is about 9156 Pa/m. Correspondingly, for the superimposed calculation of the body-centered cubic pebble bed, the parameters are 57.11 K/m,54.67 K/m and 5327 Pa/m respectively. It shows that the rise rate of the average temperature of helium gas of body-centered cubic pebble bed is higher than the simple body-centered cubic pebble bed and the pressure drop is lower. Based on the above parameters, the paper fitly calculates the rise rate of temperature and drop rate of pressure of body-centered cubic pebble bed at different superficial velocity. This research has some meaning for the design of high temperature gas cooled reactor.