Modelling of azimuthal effects arising from interaction between clad deformation and heat transfer under LB LOCA conditions

Abstract

The study of clad ballooning and the subchannel blockage arising from it is an important part of LWR safety research. A large amount of experimental data has been obtained over the years which has shown the importance of thermohydraulic effects on the clad ballooning process. Thus the distribution of clad strain, both azimuthally and axially within a fuel bundle are critically dependent on the detailed temperature distribution. Azimuthal clad temperature variations arise because of variations around the rod of pellet-clad gap, neutron flux, coolant temperature and surface heat transfer. They determine the pattern of straining but are also strongly influenced by it. A simple 3D computer model RODSWELL is being developed specifically to investigate the interactions between deformation and heat transfer. It is being used to identify the accident conditions potentially capable of producing significant subchannel blockage and to quantify the various parameters needed in the design of meaningful simulation experiments.