A multi-annulus heat conduction model for predicting the peak temperature of nuclear fuels with randomly dispersed TRISO particles

The conventional homogenous heat conduction model is capable to calculate the average temperature of the FCM fuels with randomly distributed TRISO particles. However, it is not able to predict the peak temperature due to the dispersed internal heat sources. As a complement of the conventional homogenous model, a Multi-annulus heat conduction model is proposed to capture the peak temperature for the FCM fuels. In this model, the FCM fuel pellet is divide into several annular regions and each annulus region consists of two parts: annular matrix subregion and annular fuel subregion. Then the heat transfer in the FCM fuels is simplified to a one-dimensional heat conduction model. It is found that the peak temperature by the Multi-annulus model is very close to that by the Multi-region model, in which the three-dimensional heat transfer in the randomly distributed TRISO fuel particles is completely solved. The number of the annular regions greatly affects the peak temperature. The Multi-annulus heat conduction model with 9 annular regions is recommended for predicting the peak temperature when the packing fraction is in the range of 0.35–0.45. This work could assist the thermal and safety design of the nuclear reactors with FCM fuels.