Nonlinear FEM-Based Sensitivity Analysis of a Grid Spring in a Nuclear Fuel Assembly.

The structural sensitivity analysis for elasto-plastic problems is more difficult than that for the other nonlinear problems because of the path dependency of sensitivity. In this paper, the sensitivity analysis method that the authors have developed is applied to a realistic example of an elastic-plastic large displacement problem of a grid spring which supports fuel rods in a PWR. The sensitivity of the reaction force and maximum Mises stress with respect to the thickness of the spring is analyzed. The sensitivities obtained by the present method are compared with those by the finite difference method to show the good agreement. The stochastic finite element analysis is also exemplified based on the sensitivities and the experimental data of the random thickness of the spring.