Thermal hydraulics modeling of On-line refueling for the Advanced High Temperature Reactor (AHTR)

•A methodology developed for thermal-hydraulic analysis of fluoride salt cooled reactor (AHTR)•ANSYS/Fluent used for 2D/3D thermal-hydraulic simulations of online refueling.•Online refueling causes asymmetric temperature and flow distribution in upper/lower plenum.•Recommendations on the assembly design are provided to reduce the lift force.•The study demonstrates the viability of online refueling for improving the economics of the AHTR. As part of the effort to move forward the Fluoride salt-cooled High-temperature Reactor (FHR) technology, the Advanced High Temperature Reactor (AHTR) is being developed at Oak Ridge National Laboratory (ORNL) and several other institutions. Due to its plank fuel design and inherently low heavy metal loading, which challenges fuel utilization, online refueling is considered as an option for improving the economic viability of this reactor. This work presents the thermal hydraulic modeling of the online refueling for the AHTR. Analyses at the single channel and fuel assembly level have been performed in order to develop a model of the reactor. The reactor modeling has been integrated with CFD studies for characterizing the steady state conditions and the refueling transient. The simulations of the transient have been complemented by the analysis of the stability of the refueling operation. This work demonstrates the viability of online refueling from a thermal hydraulic standpoint and develops a modeling approach for this type of operational transient.