Analysis of Temperature Drop Along the Radial Axis in Steady State Heat Transfer of Nuclear Fuel Element Using ANSYS APDL

Abstract

Nuclear reactor core is usually made up of cylindrical fuel elements that contain fuel pellets, helium gas gap and cladding material. In this paper our goal was to analyze the temperature drop from the centerline of the fuel where the maximum temperature occurs, to the gas gap and then finally to the cladding surface. The geometrical, physical and thermal properties of the fuel element are known. The Nuclear fuel element used in this calculation was UO2, which is the standard fuel element for Light Water Reactors. We used two techniques to solve this problem. The First Technique was to try to obtain an exact solution of the steady state analysis using the classical heat conduction equation. The second approach was to use FEA which is inbuilt in ANSYS APDL, where the partial differential equation is automatically solved numerically using finite different method. The results were compared and the conclusion was that the addition of gas gap between the pellet and the cladding material further contributes to the increase in the centerline temperature. The bigger the thickness of the gap, the higher the centerline temperature, this is due to the fact that the thermal conductivity of helium gas is very low, hence it is not very good at carrying heat from one surface to another. This is partly the reason why the thickness of the gas gap is usually very small.