Review of experimental models and findings on gas entrainment by vortex in hot plenum of sodium fast reactors

The presence of gas above the free surface in the hot plenum can have significant safety implications for Sodium Fast Reactors, as gas pockets within the core can affect neutron behavior and potentially lead to variations in core reactivity. One of the primary mechanisms for gas entrainment into the core is associated with vortices formed at the free surface. In response to this observation, extensive studies have been conducted to assess the risk of vortex-induced gas entrainment. Given the complexity and high cost of conducting experiments with sodium, most studies have employed water as a simulant fluid using a similarity approach. These studies generally fall into two categories: one involving basic geometries to identify the key phenomena driving vortex formation, and the other involving scaled models of actual reactor designs aimed at safety assessment and validation of numerical tools. This article provides an overview of past models used to study gas entrainment and highlights the main findings achieved through these studies.