Prediction of the dynamical thermal behavior of a HTGR multilayered spherical fuel particle using lumped and distributed parameter models

In this work, we studied the transient heat conduction in a coated fuel particle (TRISO). The analysis was carried out by using both the lumped parameter model and the distributed parameter model for comparison, which is solved by an implicit finite difference method. The lumped model approach requires lower computational efforts, allowing a fast evaluation of the average temperatures of all the five regions of the TRISO particle, while the distributed model approach provides an accurate evaluation of the approximate solution obtained by the lumped model. The two-point Hermite approximations for integrals were utilized in the lumped model approach for the average temperature and for the heat flux in each layer. For the average temperature, the plain trapezoidal rule (H0,0 approximation) and the two-side corrected first order trapezoidal rule (H1,1 approximation) were used in all layers, except for the innermost layer (UO2), where the second-order one-side corrected trapezoidal rule (H2,0 approximation) and the second-order two-side corrected trapezoidal rule (H2,1 approximation) were used. For the heat flux, the plain trapezoidal rule (H0,0 approximation) was utilized for all the layers. The finite difference solution employed 4001 points for the discretized dimension parameter and 50000 steps in time. The mechanical properties (thermal conductivity and specific heat) of the materials were supposed to be constant in function of the temperature and uniform in each region. (author)