Engineering aspects in modeling of high burnup LWR fuel behavior

Suzuki, Motoe

In designing a fuel performance code which describes complicated interactions working in high burnup fuel, the code will inevitably become a complex structure of inter-dependent models. In normal operation conditions, PCMI occurs and the pellet-clad firm bonding layer makes the cladding to be subjected to a bi-axial stress state, i.e. under tough mechanical loading. In contrast, the bonding layer enhances thermal conductance, decreases the pellet temperature and keeps the pellet-clad contact, resulting in increased resistance against the Lift-Off. For pellet behaviors, the fission gas bubble growth is strongly dependent on temperature, so that a reliable prediction of fuel temperature is required by pellet radial meshing which can fully accommodate the burning analysis results and the rim structure growth. The presentation deals with modeling method in terms of specific aspects such as meshing.