Dust explosion hazard in ITER: Explosion indices of fine graphite and tungsten dusts and their mixtures

Addressing the dust explosion hazard in ITER, a standard method with a 20-l-spherical combustion chamber was used to measure the explosion indices of fine graphite and tungsten dusts and their mixtures. The indices include maximum overpressure, maximum rate of pressure rise, and lower explosion concentration limit. The effect of dust particle size was studied on the explosion behaviour of graphite dusts in the range 4–45 μm. The explosion indices of 1 μm tungsten dust and its mixtures with 4 μm graphite dust were measured. The graphite dust particle size is shown to have a profound effect on the explosion characteristics. The finest dust features the highest maximum overpressure and rate of pressure rise, and the lowest explosible concentration. Four tungsten/graphite dust mixtures with molar ratios of W/C = 1/30, 1/4, 1/1, and 3/1 were tested at the concentrations at which the dust combustion consumed all the oxygen in air producing maximum overpressures and rates of pressure rise. The maximum overpressure decreases slightly with increasing tungsten content, while the maximum rate of pressure rise has a pronounced peak at W/C=1/1, i.e. this mixture burns faster than both pure graphite and pure tungsten dusts alone. All the tested dusts belong to the mildest explosion class.