Computational fluid dynamics and simulation-based-design approach for tight lattice nuclear fuel pin subassemblies

This paper is a review of some of the recent achievement in computational fluid dynamics (CFD) being used or to be used in nuclear reactor thermal hydraulics analysis. We focus on the aspects of CFD that are most relevant to the tight lattice nuclear fuel pin subassemblies that are considered for future nuclear reactor core options, including those in light water reactors being aimed at a high burn-up or a long life core and, in general, sodium-cooled fast reactors. We will illustrate, in particular, turbulence phenomena that have been identified by CFD and peculiar to the flows in tight lattice nuclear fuel subassemblies, eccentric annuli and rectangular channels interconnected by a narrow gap. Highlighted phenomena include turbulence-driven secondary flows inside a subchannel, local turbulent-laminar transition in the narrow gap region between two adjacent fuel pins, and global pulsation of the flow across the length of a fuel subassembly. Special attention will be paid on linkage to the physics, limitation of the computational capability of the CFD methods, and the usefulness of the technology in reference to the foreseeable future.