BOW Code Development

Abstract

A bundle version of the BOW computer program has been recently developed in AECL to simulate simultaneous elastic and elasto-creep deformations of all fuel elements within a fuel bundle under normal operating conditions. The finite element method is employed in the BOW code to model lateral deformations of all fuel-bundle components by accounting for temperature variations in the pellet and sheath, neutron flux gradient across the bundle radius, gravity, hydraulic drag force, sheath creep and pellet cracking. A reliable and convergent contact algorithm is implemented into the recent BOW code to handle the contacts among neighboring fuel elements through mating spacers, and to handle contacts of outer fuel elements with the pressure tube through bearing pads while accounting for the creep-induced sagging of the pressure tube. Simultaneous considerations of in reactor load effects and contacts introduce nonlinear factors to the solution process. This paper presents a methodology to model and solve the complex in reactor fuel-bundle deformation process. To date applications of the BOW code in nuclear fuels have shown that BOW calculations are accurate and reliable.