Dust explosion in fusion reactors: Explosion characteristics and reaction mechanism of tungsten micro-powder

Abstract

The explosion of in-vessel dusts, mainly produced by energetic plasma and wall interaction, will pose a great threat to the safe operation of a fusion reactor. Unlike dust explosions in traditional industrial systems, dust explosion in tokamak devices has the unique characteristics, including dust composition (tungsten is one of the main components), initial conditions of explosion, etc. However, the experimental data on this aspect are very few, which is not enough to support the safety assessment of fusion reactors. In this work, the experiments were used to study the explosion characteristics and mechanism of the micro-tungsten in a 20 L spherical vessel. Results showed that the lower explosion limit (LEL) of 2 µm tungsten dust was in the range of 250–500 g/m3, and the maximum explosion pressure would reach 0.46 MPa at 3000 g/m3. The factors related to fusion reactor environment, including initial pressure, ignition energies and the ignition delay time, were studied to demonstrate a significant effect on explosion parameters. The explosion product changed from WO3 to WO2.72 with the increase of nominal dust concentration. A combustion mechanism for single mirco-tungsten particle was established. Based on the experimental data, the explosion possibility and hazard of tungsten dust in fusion reactor were also dicussed.