Is reactor multiphase thermal-hydraulics a mature field of engineering science?

Abstract

Abstract The progress in multiphase science and technology has been driven to a considerable extent by the problems arising from nuclear reactor thermal-hydraulics. However, the needs for obtaining solutions to a variety of practical questions have had both pros and cons. The former have been reflected in the role of needs as an obvious research stimulation factor, the latter have been due to fact that the urgency of producing results often limited systematic investigations of the underlying physics. Consequently, the maturity of this field has been frequently questioned in the past, in particular as compared to the single-phase fluid mechanics and heat transfer. The objective of this paper is to present an overview of selected issues which, in the author’s personal opinion, illustrate the current state of knowledge in regard to various aspects of multiphase physics and its application to reactor thermal-hydraulics (TH). The discussed issues include: theoretical fundamentals of multiphase fluid mechanics and heat transfer, formulation and limitations of closure laws, transition from correlations to models, consistency vs. accuracy (or validation vs. tuning), and challenges associated with the multicomponent/multiphase modeling of core degradation phenomena. Examples shown to illustrate selected issues come from several studies performed by the author and his collaborators and associates. They cover a broad range of scales, from micro-scale phenomena at, or below, the individual bubble level, to the scale of reactor fuel assemblies. Given the complexity of the multiphase thermal-hydraulics, the author is aware that a lot of room is still available for different opinions on the current state of affairs in this field. So, the overall goal of the paper is to stimulate constructive criticism and future discussions among members of the nuclear TH community.