Modelling of Dust Resuspension in Tokamak Devices During an Air Inflow Event

Abstract

In a Tokamak-fusion reactor, the plasma interacts with the first wall generating dust of different materials. Dust can play an important, if not primary, role in determining safety and economic performance of this type of fusion machines, due to potential accident and maintenance requirements. In this paper, after a brief introduction, a description of dust explosion mechanism is reported with reference to several experiments used to create or validate theories and models. The safety concerns about dust are based on the assumption that, in case of air inflow events, this particulate can be resuspended in the vacuum vessel leading to a potential explosive cloud. In the paper the main literature models used to deal with dust transport and resuspension are reported: the VZFG model, the Rock n’ Roll model and the ECART model. Differences, pros and cons of each models are described to obtain a comparison between energy-based and force-based balance models. Finally, the numerical approach for the resuspension phenomenon is discussed and an application is shown. The simulation has been carried out with reference to a laboratory scale facility-like in 3D geometry. The simulated event is an air flow intake, as from a Loss of Vacuum Accident, and the results show the distribution of dust in the geometry after the first instants of intake, the mass concentration of particulate on the surfaces and the path lines of the flow field. The simulated geometry is only partially referred to an existing experimental facility, and the methodology could be useful to replicate the same conditions to obtain a validation of the results. More and finer simulations are foreseen to reproduce more accurately experimental data and real scenarios, with the aim to evaluate the risk of explosion by means of an accurate prediction of dust distribution inside a vacuum volume during resuspension due to air inflow.