System Thermal-hydraulics Model for Fluoride Salt-Cooled Reactor Based On Small Advanced High Temperature Reactor (smAHTR) Design Concept

A system thermal-hydraulics model for a fluoride-salt-cooled high-temperature reactor (FHR) based on the small modular advanced high-temperature reactor (SmAHTR) design concept is developed, using RELAP5-3D. The SmAHTR components modelled in the simulations include: the reactor core, lower plenum, upper plenum, top plenum, three Primary Heat Exchangers (PHX's) equipped with three primary pumps, and three Director Reactor Auxiliary Cooling System (DRACS) equipped with three fluid diodes. Flows through the reactor core are represented by 19 individual fuel channels, one reflector-hole channel, and one downcomer channel. In each of the 19 SmAHTR fuel block channels, the fuel elements are modeled in 5 groups using 5 heat structures, each with their corresponding power level. The total reactor power is 125 MWth. Using representative core power distributions for the SmAHTR at beginning-of-cycle (BOC) and at end-of-cycle (EOC), two steady-state system thermal-hydraulic model simulations with RELAP5-3D were performed using a default pressure drop loss factor of 1.5 for all 19 fuel channels. Exit coolant temperatures ranged from 688°C to 739°C (BOC) and from 696°C to 721°C (EOC), while peak fuel centerline temperatures in the highest power block were 1,249°C (BOC) and 1,029°C (EOC). By adjusting the loss factors to modify coolant flow rates in each channel, a more uniform exit coolant temperature was possible.