Prevention of hydrogen and dust explosion in ITER

It is to be expected that, over time, an interaction of plasma with walls and the divertor will create in ITER hundreds of kilograms of beryllium, carbon or tungsten dust – loose particles with characteristic diameter <100 μm. Interaction of the hot Be dust with water in the case of a water leak will produce hydrogen. In such conditions air leaks can lead to hydrogen or dust explosions. The explosions could damage the machine and would present a danger to the public if the release of radioactivity from the vacuum vessel were not otherwise mitigated. Current ITER strategy to cope with the danger of dust/hydrogen explosions is based on administrative limits on accumulation of dust inside the ITER vacuum vessel.We are investigating a different approach based on active prevention measures – injections of an inert gas (CO2) in the vacuum vessel in case of detection of air leaks.Analysis done with the code MELCOR shows that injection of CO2 in the vacuum vessel may prevent the explosions. However, a detailed analysis of O2/CO2/H2 space distributions and some experiments will be needed before a decision is made to base ITER safety on this approach.