Heat Transfer Modeling of CANDU Pressure Tube Under Localized High Temperature Condition

Abstract

The main objective of this research is to develop thermal models in order to evaluate mechanical deformation of the potential contacts between fuel elements and pressure tube in the CANDU reactor. The consequence of concern is potential creep strain failure of a pressure tube and calandria tube challenging fuel channel integrity. The initial focus will be on the case where a fuel rod contacts the pressure tube at full power with high cooling flow. Such an event could occur if a fuel element was to become detached from a bundle. The heat conduction from fuel sheath to the inner surface of the pressure tube with appropriate convective and radiation boundary conditions has been simulated. The contact boundary could be a single spot or a small arc between the fuel sheath and pressure tube. The vapor pockets are considered in the areas beside the contact region where the convective cooling is drastically decreased. Subsequently, modelling has been extended to the contact of number of fuel elements where several fuel rods are postulated to contact the pressure tube under fully cooling conditions. It is observed that pressure tube creep strain will occur if sufficiently high temperature is reached.