Development of a two-regime heat conduction model for TRISO-based nuclear fuels

Highlights: • Demonstrated a methodology for randomly distributed heat source calculation in a fuel pebble. • Developed an advanced two-regime model for TRISO fuel temperature calculation. • Peak temperature and average temperature used to validate the two-regime model. • The proposed model shows improved agreement comparing to the homogeneous model. - Abstract: Several advanced nuclear reactors use Tristructural-isotropic (TRISO) fuel particles randomly distributed in a matrix to allow for aggressive operating conditions. Since those fuels are composites with randomly distributed fuel particles in a matrix, suitable smearing methods are needed to obtain fuel temperature fields for reactor design and safety analysis. By developing three-dimensional finite-element heat conduction models for randomly distributed heat generating particles in a matrix, this study evaluated the impact of the randomly distributed heat sources on the temperature fields of the fuel pebble. In addition, a two-regime heat conduction model was proposed in this study by assuming that all fuel particles are densely packed at the center of the fuel element. The present model provides a practical methodology to predict peak and average fuel temperatures of nuclear fuel elements with heat generating particles because, among the possible distribution patterns of the TRISO fuel particles, the peak fuel temperature is highest when all the fuel particles are densely packed at the center of the fuel element. Comparing to other models, the present model predicts more conservative temperature fields and shows improved agreement with both peak and average fuel temperatures of the simulated compacts and pebbles.