Pronghorn: Porous media thermal-hydraulics for reactor applications

Pebble bed High Temperature Reactors (HTRs) are characterized by many advantageous design features, such as excellent passive heat removal in accidents and large margins to fuel failure. However, a significant challenge in thermal-hydraulic core modeling of pebble bed reactors is the double heterogeneity random packing of hundreds of thousands of fuel pebbles and thousands of fuel particles per pebble. A new porous media thermal-hydraulics code, Pronghorn, is under development to provide a fast-running, medium-fidelity core simulator and serve as a bridge between low-resolution system level codes and high-resolution Computational Fluid Dynamics (CFD) codes for multiscale analysis. Pronghorn is based on the Mul-tiphysics Object-Oriented Simulation Environment (MOOSE) finite element framework, and permits an arbitrary equation of state, unstructured mesh capabilities, modern software design, and the ability to couple to MOOSE fuels performance and systems-level Thermal-Hydraulic (T/H) codes. To address the wide variety in gas- and liquid-cooled pebble bed reactor designs, Pronghorn includes several different flow models, each most appropriate to a range of compressibilities and operating conditions. This paper reviews benchmarking efforts of a low-advection flow model appropriate for Loss of Forced Circulation (LOFC) simulations and introduces the new fully compressible flow model with preliminary validation by comparison to potential flow theory for low Mach number flow over a cylinder.