Measurement of Dust Mobilization in TDMX

Operation of ITER is expected to produce substantial quantities of particulate material in the form of dust, flakes, and spalled deposits from erosion of plasma facing components. Such material may contribute to hazards associated with potential ITER accident scenarios. For example, beryllium dust residing on a hot surface may react vigorously with moisture introduced into the vacuum vessel during a loss of vacuum accident with a coolant line rupture. Hydrogen results from the reaction, possibly creating an explosive atmosphere within the vacuum vessel. Additionally, dust may be activated (in the case of tungsten) or retain tritium (in carbon), thereby contributing to environmental release and the associated site source term for postulated accident scenarios. Development of defensible safety analyses for ITER relies on detailed understanding of dust re-suspension, mobilization, and release during accident simulations. An experiment facility has been developed at the Idaho National Laboratory, Idaho, USA, to investigate these issues and provide benchmark data for dust transport in ITER safety analyses. The Toroidal Dust Mobilization eXperiment (TDMX) simulates dust re-suspension, mobilization, deposition, and release during loss-of-vacuum ingress with a configuration similar to ITER. Vacuum chamber geometry is defined by two coaxial, plexiglass cylinders sealed on their ends. The height-to-diameter ratio of the outer cylinder was chosen to be consistent with and scalable to the ITER design. Vertical and horizontal port extensions represent locations removed from the main torus for air ingress or trapped volumes for dust deposition. Simulated structures, e.g. divertor dome and baffles, may also be placed in the vessel for testing dust trapping underneath obstacles. A set of experiments has been performed with TDMX to measure the mobilization fraction, distribution of deposition, and release fraction of dust characteristic of that expected in ITER. Measurements were performed for various chamber pressurization rates and initial dust locations. No internal structures were used for these tests. Dust species included carbon, alumina, and tungsten; tests were performed for each material separately and in mixtures. This paper presents the results of the investigation and describes the potential impact on ITER safety analyses. (author)