ETOILE: A three-dimensional finite element code for analyzing fuel pin deformations in an LMFBR assembly

Computer program ETOILE has been developed for the purpose of predicting irradiation behaviour of fuel pins in a fuel subassembly under steady state conditions in LMFBR cores. This report describes the analytical models and numerical procedures together with some typical results obtained by the code. ETOILE is programmed with the FORTRAN-IV capable of treating up to 271 fuel pins in a subassembly, and up to 20 turns of spiral wires. The finite element method is employed in the code to perform the three-dimensional structural analysis of the full bundle model. In order to represent the non-linear stiffness caused by contacts and separations between adjacent pins, a new joint element has been developed. A model for treating the effect of wire tension is included in the code to simulate the pin and wire mechanical interaction caused by different dimensional change between the wire and the fuel cladding during irradiation. With the finite element method for discretization of the structural equations, a set of non-linear equations is obtained. To solve the non-linear equations, an iteration technique is used. Two iteration loops are used, one is the outer iteration loop concerning the non-linearity due to wire tension, and another is the inner iteration loop concerning the non-linearity due to contact and separation. For the acceleration of inner iteration, the Newton-Raphson method is adopted. In each iteration step, the linear matrix equation, which is often the king size matrix equation, must be reconstructed and then solved. To solve the linear matrix equation, the block successive over-relaxation method is adopted. To see the effect of wire tension, some analyses were made on the two subassemblies containing 169 and 37 fuel pins respectively. As a result, it was shown that there were significant effects of wire tensions on the equilibrium configuration of fuel pins in both cases. This work was performed under the sponsorship of Toshiba Corporation. (orig.)