J.P.Sharpe, M.A.Bourham, J.G.Gilligan
Department of Nuclear Engineering
North Carolina State University, Raleigh, NC 27695
Disruption events in future tokamak reactors are expected to be intense due to high energy inventory within the confined plasma. For example, the proposed International Thermonuclear Experimental Reactor (ITER) has the potential for disruption heat loads up to 100 MJ/m2 incident upon the divertor area in a 10 ms time period. Such events can cause severe vaporization and melting of exposed material. Disruptions are generally included in accident scenarios and contribute significantly in reactor safety analyses. Of particular concern regarding reactor safety following a hard disruption is aerosol generation from activated plasma-facing materials.
In order to generate defensible safety analyses for future tokamak reactors, disruption effects on plasma-facing materials and subsequent aerosol formation mechanisms should be well understood and benchmarked with a relevant materials database. One technique for disruption simulation involves the use of an electrothermal (ET) plasma source. The ET facility SIRENS at North Carolina State University has been modified to study disruption-induced aerosol mobilization for ITER relevant materials. Particle transport properties obtained from experiments will contribute to a materials database for use in ITER safety analysis.
Electrothermal plasma sources have been used to simulate disruptions because magnitudes and physical mechanisms of heat transfer in the ET source are very similar to those in a tokamak disruption. Changes to the SIRENS facility have allowed experiments in which test material is vaporized within the narrow ET source and expanded into a large chamber. This expansion generates aerosol particles in a fashion similar to those from hard disruptions expected in ITER. This paper will outline the aerosol generation processes occurring in the experiment and report measured particle size distributions for the various materials tested (copper, stainless steel, tungsten, and graphite).
*Work supported by The U.S. Department of Energy, Office of Energy Research, under contract DE-FG02-96ER54363.