Novel scaling law for long-term interface displacement of a stratified layer by erosion mixing due to turbulent impinging jet applicable to nuclear power plants

Abstract

The distribution and mixing characteristics of hydrogen gas are important for assessing the hydrogen risk in nuclear power plants (NPPs) during severe accidents. To estimate such characteristics, analyzing the erosion mixing process of a stratified hydrogen layer subject to a turbulent impinging jet is necessary. In this paper, we propose a novel scaling law for the interface displacement of a stratified layer by erosion mixing as the result of a turbulent jet impingement in a long-term transient state. We show that interface displacement has nonlinear and time-dependent relationships with flow conditions such as the competitive force between the turbulent jet and stratified layer, as well as geometric parameters such as the vessel diameter. We extend the mass conservation law for the entrainment of a stratified layer over a long elapsed time by incrementally using a scaling law for the entrainment rate that is valid at a quasi-steady state. As a result, we show that the novel scaling law for the long-term interface displacement depends on the elapsed time, vessel diameter, and competitive force. The results obtained in previously reported containment flows experiments, as well as those obtained in the present study, are in good agreement with the prediction by the proposed scaling law, demonstrating that this law would be useful for predicting the behavior of the interface displacement of a stratified layer by erosion mixing under various conditions.