Physics-based multiscale coupling for full core nuclear reactor simulation

•We describe recent “MultiApp” and “Transfer” technologies in the MOOSE framework.•Neutronics, fuel performance, thermal fluids, and mesoscale phenomena are simulated.•Results presented for 3D KAIST-3A benchmark and AP1000 reactor geometries.•CRUD Induced Power Shift phenomenon observed in simulation with 3432 fuel rods.•Fuel shuffle capability demonstrated across 41448 fuel rods in 157 assemblies. Numerical simulation of nuclear reactors is a key technology in the quest for improvements in efficiency, safety, and reliability of both existing and future reactor designs. Historically, simulation of an entire reactor was accomplished by linking together multiple existing codes that each simulated a subset of the relevant multiphysics phenomena. Recent advances in the MOOSE (Multiphysics Object Oriented Simulation Environment) framework have enabled a new approach: multiple domain-specific applications, all built on the same software framework, are efficiently linked to create a cohesive application. This is accomplished with a flexible coupling capability that allows for a variety of different data exchanges to occur simultaneously on high performance parallel computational hardware. Examples based on the KAIST-3A benchmark core, as well as a simplified Westinghouse AP-1000 configuration, demonstrate the power of this new framework for tackling—in a coupled, multiscale manner—crucial reactor phenomena such as CRUD-induced power shift and fuel shuffle.