An Investigation of Structural Strength of Nuclear Fuel Spacer Grid

This paper compares and discusses the methods for evaluation of the structural integrity of the mid spacer grid of nuclear fuel assembly via a finite element analysis of 3D shell elements. The structural stiffness of the spacer grid is determined by applying either force or deformation as loads onto the spacer grid for both the square load and shear load directions. This study is an extension of a single-cell strength analysis of a spacer. External events such as seismic activities that might happen in a nuclear reactor are able to transfer loads onto nuclear components in random directions, which can be broken down into square and shear loadings. The structural strength indicated by the force reaction against the input displacement load was proven to be smaller such that the same displacement square load is around 260 times greater than the shear load. Due to the weakness in shear stiffness, the maintenance of a spacer grid structure is more vulnerable against out-of-plane loads. This indicates that the shear load needs to be considered in studies of fuel assembly integrity assessment for newly developing fuel design, as well as existing fuel assembly designs.