Finite Element Analysis of Optimized H Shape Spring in a Nuclear Fuel Spacer Grid by using Contact Definition

Abstract

The primary role of the grid springs in a spacer grid is to hold the fuel rods in an appropriate position using a friction force and to prevent the fuel rods from dropping during a normal reactor operation. Spring force decreases as the fuel burn-up increases since the spring stiffness is degraded by the high temperature and irradiation effects in a reactor core. So this phenomenon has to be considered when the initial spring force of a grid spring is being determined. To check whether a spring has a suitable spring force, characterization tests of a spring are conducted. In this paper, an analytical verification work, a FE model using contact definitions, is established for predicting the spring stiffness without any spring test. Finally, the test and analysis results are carefully compared to check the availability of a finite element model for investigating the spring characteristics at an in-grid boundary condition.