CFD and systems thermal-hydraulic analysis in the design and safety assessment of high-temperature reactors

An overview is provided of the role of the various levels of CFD in the different stages of the design, analysis and evaluation of very-high-temperature reactor (VHTR) systems and molten salt reactor (MSR) systems. The biggest challenge in this regard is to satisfy all the phenomenological, physical and time scales in a single model of the complete reactor unit. This is currently not practically feasible but rather addressed by employing models at various levels of abstraction and detail. Simulation models that encompass a large geometrical and temporal scope, such as 1D plant-wide system models, typically use reduced-order models to represent underlying phenomena. For gas-cooled pebble bed reactors a significant amount of work has been done to characterize the flow and heat transfer characteristics within the bed. For prismatic block gas-cooled reactors model development is also well advanced. Gas-cooled reactor systems in general have also been analysed exhaustively at the larger system level. In the case of liquid fuel MSRs the focus has been on multiphysics approaches wherein the neutronics are coupled with the thermal-hydraulics in order to account for the neutron precursor drift due to the velocity field. The CFD work on solid fuel MSRs employed either a porous media approach, or if the discrete element approach was employed, only focused on a very small representative unit cell geometr