(The) analysis of fuel rod behavior using finite element method

Abstract

The Fuel Road Analysis (FURA) code is developed using two-dimensional finite element analysis for axisymmetric and plane stress system of fuel rod. It predicts the thermal and mechanical behavior of fuel rod system during normal and load follow operations. To evaluate the exact temperature distribution and inner gas pressure, the radial deformation of pellet and clad, the fission gas release are considered full-length fuel rod. The thermal element equation is derived using Galerkin``s technique. The displacement element equation is derived using the principle of virtual works. The mechanical analysis can accommodate various component of strain: elastic, plastic, creep and thermal strain, as well as strain due to swelling and densification. The 4-node quadratic isoparametric elements are adopted, and the geometric model is confined to a half-pellet-height region with the assumption that pellet-pellet interaction is symmetrical. The pellet cracking and crack healing, pellet-cladding interaction are modelled. The Newton- Raphson iteration with an implicit algorithm is applied to perform the analysis of non-linear material behavior accurately and stably. The pellet and cladding model has been compared with both analytical solutions and experimental results. The observed and predicted results are in good agreement. The general behavior of fuel rod system is calculated by axisymmetric system and the cladding behavior against radial crack is used by plane stress system. The sensitivity of strain aging of PWR fuel cladding tube due to load following is evaluated in terms of linear power, load cycle frequency and amplitude.