A Review of Models for the Sodium Boiling Phenomena in Sodium-Cooled Fast Reactor Subassemblies

The Euratom Horizon-2020 project European sodium fast reactor safety measures assessment and research tools (ESFR-SMART) aims to enhance the safety and performance of the European sodium-cooled fast reactor (ESFR) considering safety objectives envisaged for generation-IV reactors and the update of European and international safety frameworks, taking into account the Fukushima accident. Further, the project aims to support the development and validation of the computational tools for the situations to be considered at each defense-in-depth level in order to support the safety assessments using data produced in the project as well as selected legacy data. Within this activity, the focus is on the assessment and when needed further development of computer codes for the analysis of the sodium thermal-hydraulics phenomena in sodium cooled fast reactor (SFR) sub-assemblies under operational and accidental conditions including sodium boiling and transitional convection from forced to natural/mixed convection. In support of this activity, a review is performed for the sodium boiling models used in the codes participating in benchmark activities within the project. The objective of this paper is to summarize the result of the review, which encompasses both the phenomenological and mathematical models implemented in the codes. In particular, the review addresses the physical bases of sodium boiling models, the analytical models in connection with the numerical implementations in the codes, and the geometry representations ranging from a one-dimensional single channel and finite volume to full three-dimensional computational fluid dynamics (CFD) and porous media representations. Finally, the needs for further developments are discussed.