Preliminary Study on Optimization of a Bulge Tool for Nuclear Fuel Manufacturing

Abstract

A nuclear fuel assembly, manufactured through several processes, is composed of a range of components. Guide thimbles and spacer grid sleeves, among others, are particularly important to maintain the integrity of fuel assembly, and they are connected through a bulge forming process. The purpose of the bulge process for fuel assembly is to connect guide thimbles to spacer grids. The connecting load between tubes is affected by bulge joint strength, and this strength depends on bulge design. While reaching to a specified load, bulge equipment endures high working loads during the working process, and a cracked tool can be seen infrequently. The equipment consists of a bulge tool and a taper pin, and the neck of the bulge tool is most susceptible to damage. A crack may appear in fuel assembly when the bulge tool is broken during the bulge process. The optimization of bulge equipment is difficult because the bulge process has geometric nonlinearity, boundary nonlinearity, and material nonlinearity. The work velocity of the bulge process for nuclear fuel manufacturing is relatively slower than that of general forming processes, but a stroke is very important. Therefore, nonlinear analysis should be required in the optimization process. In this research, the design of experiments using an orthogonal array and the finite element analyses are employed to determine the optimal shape and material. Design variables are the material and three types of local shapes of a bulge tool, and the level of the design variables is three. The objective of the optimal design is to reduce the maximum stress imposed on a bulge tool. The commercial software, ABAQUS, is utilized for nonlinear static analysis of the bulge process, and L9 orthogonal array is used for the optimization of the bulge tool.