Development of NUFORM3D module with FRAPCON3.4 for simulation of pellet-cladding mechanical interaction

In order to evaluate the PCMI (pellet-to-cladding mechanical interaction) behavior in fuel rods, a three-dimensional finite element (FE) module, termed NUFORM3D, was developed by KAERI. In the NUFORM3D module, a thermo-mechanical model considering elasto-plastic deformation and a contact model were formulated to simulate the PCMI behavior. The NUFORM3D module was implemented to compensate for the weaknesses of the analytical methods used in traditional fuel performance codes for PCMI simulations. In this work, NUFORM3D was coupled with FRAPCON-3.4, which is the NRC's fuel performance code for a steady state, to evaluate the NUFORM3D module with an irradiated database. The REGATE experiment, involving the use of a power ramp database in a test reactor, was employed to evaluate the coupled code system. The coupled NUFORM3D was able to simulate bamboo-shaped deformation of cladding as well as stress concentrations in cladding due to pellet hourglass deformation in the power ramp. Secondary ridges of the cladding on the mid-pellet plane were found in the experimental results. To simulate the secondary ridge, a transversally fragmented pellet model was adopted. As a result, the coupled NUFORM3D module can improve the simulation capability of fuel performance codes for PCMI.