Hydrogen/dust explosion hazard in ITER: Effect of nitrogen dilution on explosion behavior of hydrogen/tungsten dust/air mixtures

The work is aimed at supporting inert-gas dilution method proposed to mitigate hydrogen/dust explosion hazard in ITER in case of severe accidents. A standard method of 20-1 sphere is used to study the effect of nitrogen dilution on the explosion behavior of 0.5-mu m tungsten dust dispersed in hydrogen-containing air atmospheres. The oxygen content varied from normal 21 to 10 vol.%. The hydrogen concentration was varied from 7 to 18 vol.%; the tungsten dust cloud density of 2 kg/m(3) was chosen to test as the optimal, i.e. the most dangerous dust concentration. The tested mixtures were formed in a spherical combustion chamber of 20-1 volume at normal initial conditions and ignited at its center by a weak electric spark. In general, the tested dust/hydrogen mixtures explode more dangerously than hydrogen alone: they can generate higher explosion overpressures and explode faster than the corresponding hydrogen/air mixtures without dust. For all the tested mixtures the nitrogen dilution reduces both the explosion overpressure and pressure rise rate; however, its influence is more pronounced on how fast combined explosions proceed. In case of 7 vol.% H(2), the explosion overpressure decreases from 4.5 to 3.5 bar at O(2) decrease from 21 to 10 vol.%, while the pressure rise rate drops from 400 to 60 bar/s. In case of 18 vol.% of H2, the corresponding values are 6.2-2.6 bar explosion overpressure and 1370-170 bar/s pressure rise rate. An extrapolation of the obtained results to lower oxygen concentrations gives the value of limiting oxygen concentration, at which the combined explosions are to be suppressed, about 8-9 vol.%. (C) 2010 Elsevier B.V. All rights reserved.