Progress in reflood thermal hydraulics studies in the past 40 years

Accurate simulation of reflood transients of a reactor core is one of the top priorities for nuclear reactor thermal–hydraulic and safety analysis. An in-depth understanding of the two-phase flow and heat transfer process during reflooding can provide extremely useful information on the design and analysis of the various safety systems as well as on the development of numerical analysis tools. In the current paper, the status of the reflood transients in the past several decades is overviewed and discussed in detail, in the hope to provide a roadmap for future relevant research. Following an introduction of the current topic, the phenomenological aspects related to reflood are discussed first. Then, studies on the two-phase flow thermal–hydraulic non-equilibrium are reviewed and evaluated critically. The flow channel pressure drop as well as the spacer grid effect constitute important parts of reflood thermal–hydraulic and safety analysis, and various studies on these topics are discussed. Another important consideration during reflood transients is the liquid droplet behavior since it affects the rod bundle thermal response. In addition, the current paper also identifies the several limitations and the need for future research work on reflood thermal hydraulics.