Research On Dust Migration And Hydrogen Risk Caused By Dust In Fusion Device

International Thermonuclear Experimental Reactor(ITER)is a Tokamak.After the long-term operation of ITER,there will be lots of dust generated in the ITER vacuum chamber by reason of the fast atoms and ions' bombarding and so on.In case of an accident,the dust explosion risk casued by dust migration and the hydrogen risk caused by the chemical reaction of dust may seriously threaten the safe operation of ITER.In this paper,the computational fluid dynamics(CFD)method was used to study the dust migration characteristics and the hydrogen risk caused by dust in fusion device from the experiment level and system level.The specific research includes four aspects as follows:(1)The computational model of dust migration was established based on the STARDUST experimental device.The influences of dust physical properties and obstacles on the migration characteristics were studied.The results show that: when the dust density and the particle size are smaller,the motion trajectory of dust is closer to that of gas;the existing of obstacles can limit the dust migration greatly.(2)The computational model of dust distribution was established based on the ITER device.The distribution characteristics of dust in the ITER vacuum chamber during a loss of vacuum accident(LOVA)were studied.The results show that: the average volume fraction of dust particles first decreases and then remains approximatively constant as the height increases;the average volume fraction of dust particles first increases and then remains approximatively constant as time goes;when the maximum entrainment ability of air is reached,the dust distribution in the space will not vary obviously with the initial dust mass increasing.(3)The computational model of hydrogen mixing was established based on the LSGMF device.The mixing behavior of hydrogen and the mitigation effect of nitrogen and steam inerting on hydrogen risk were respectively analyzed.The results show that: when the inlet mass flow is constant,the concentration distribution of helium varies little with the inlet velocity increasing;with the inlet mass flow increasing,the mitigation effect of nitrogen inerting on hydrogen risk will also be further improved;in the cases of different injection directions,there is an obvious local difference for the mitigation effect of nitrogen inerting on hydrogen risk;in the cases of the same inlet mass flow,the mitigation effect of steam inerting on hydrogen risk is better than that of nitrogen inerting.(4)For the accident sequence of "wet bypass",the hydrogen risk of the entire ITER vacuum chamber was analyzed in the cases of different hydrogen production rates and different mass flows of coolant.The results show that: the increasing of the mass flow of coolant may lead to the mitigation of hydrogen risk while the effect of the increasing of hydrogen production rate on the hydrogen risk state of the entire vacuum chamber needs comprehensive consideration.The research in this paper will help to strengthen the understanding of the dust safety in the ITER device and will help to formulate the relevant elimination or mitigation strategies in the future.