Three-dimensional single-channel thermal analysis of fully ceramic microencapsulated fuel via two-temperature homogenized model

• Two-temperature homogenized model is applied to thermal analysis of fully ceramic microencapsulated (FCM) fuel.
• Based on the results of Monte Carlo calculation, homogenized parameters are obtained.
• 2-D FEM/1-D FDM hybrid method for the model is used to obtain 3-D temperature profiles.
• The model provides the fuel-kernel and SiC matrix temperatures separately.
• Compared to UO2 fuel, the FCM fuel shows ∼560 K lower maximum temperatures at steady- and transient states.

The fully ceramic microencapsulated (FCM) fuel, one of the accident tolerant fuel (ATF) concepts, consists of TRISO particles randomly dispersed in SiC matrix. This high heterogeneity in compositions leads to difficulty in explicit thermal calculation of such a fuel. For thermal analysis of a fuel element of very high temperature reactors (VHTRs) which has a similar configuration to FCM fuel, two-temperature homogenized model was recently proposed by the authors. The model was developed using particle transport Monte Carlo method for heat conduction problems. It gives more realistic temperature profiles, and provides the fuel-kernel and graphite temperatures separately.In this paper, we apply the two-temperature homogenized model to three-dimensional single-channel thermal analysis of the FCM fuel element for steady- and transient-states using 2-D FEM/1-D FDM hybrid method. In the analyses, we assume that the power distribution is uniform in radial direction at steady-state and that in axial direction it is in the form of cosine function for simplicity. As transient scenarios, we consider (i) coolant inlet temperature transient, (ii) inlet mass flow rate transient, and (iii) power transient. The results of analyses are compared to those of conventional UO2 fuel having the same geometric dimension and operating conditions.