SIMULATION OF THE STATIC MECHANICAL BEHAVIOUR OF A PRESSURIED WATER REACTOR FUEL ASSEMBLY

摘要

The paper presents the mathematical modelling and computer simulation of static mechanical response of a PWR fuel assembly, with the help of the finite element code "CAST3M" developed by CEA. In PWR core analysis, the fuel assemblies present non-linear behaviour, which can be explained by the variations of stiffness due to the contact and the slipping between fuel rods and spacer grids as well as to the loss of contact of the rods. In the first part of this paper, a rod-to-grid contact model, based on the Coulomb law and constituted of non-linear springs and hinges, is developed to simulate the holding system of fuel rods inside the grid cells. The results of simulation showed a quite good agreement with the numerical reference model. The second part aims at applying the domain decomposition methods to the modelling of the fuel assembly with the proposed contact model. Due to geometric complexity of the fuel assemblies, the approximation by finite element method leads to a large number of unknowns. The resolution of this system would be prohibitively expensive with the available computation power. By using the domain decomposition methods we are able to reduce a significant amount of computational time and relieve the memory requirement from the advantage of parallel computing.