Particulate Generation During Disruption Simulation on the SIRENS High Heat Flux Facility

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Title: Particulate Generation During Disruption Simulation on the SIRENS High Heat Flux Facility
Author: Sharpe, John Phillip
Advisors: Mohamed Bourham, Chair- NE, Member
John Gilligan, Co-Chair - NE, Member
Kuruvilla Verghese, NE
Christopher Roland, PY
David Petti, INEEL
Abstract: Successful implementation of advanced electrical power generation technology into the global marketplace requires at least two fundamental ideals: cost effectiveness and the guarantee of public safety. These requirements can be met by thorough design and development of technologies in which safety is emphasized and demonstrated. A detailed understanding of the many physical processes and their synergistic effects in a complicated fusion energy system is necessary for a defensible safety analysis. One general area of concern for fusion devices is the production of particulate, often referred to as dust or aerosol, from material exposed to high energy density fusion plasma. This dust may be radiologically activated and/or chemically toxic, and, if released to the environment, could become a hazard to the public. The goal of this investigation was to provide insight into the production and transport of particulate generated during the event of extreme heat loads to surfaces directly exposed to high energy density plasma. A step towards achieving this goal was an experiment campaign carried out with the Surface InteRaction Experiment at North Carolina State (SIRENS), a facility used for high heat flux experiments. These experiments involved exposing various materials, including copper, stainless steel 316, tungsten, aluminum, graphite (carbon), and mixtures of carbon and metals, to the high energy density plasma of the SIRENS source section. Material mobilized as a result of this exposure was collected from a controlled expansion chamber and analyzed to determine physical characteristics important to safety analyses (e.g., particulate shape, size, chemical composition, and total mobilized mass). Key results from metal-only experiments were: the particles were generally spherical and solid with some agglomeration, greater numbers of particles were collected at increasing distances from the source section, and the count median diameter of the measured particle size distributions were of similar value at different positions in the expansion chamber, although the standard deviation was found to increase with increasing distances from the source section, and the average count median diameters were 0.75 micron for different metals. Important results from the carbon and carbon/metals tests were: particle size distributions for graphite tests were bi-modal (i.e. two distributions were present in the particle population), particles were generally smaller than those from metals-only tests (average of 0.3 micron), and the individual particles were found to contain both carbon and metal material. An associated step towards the goal involved development of an integrated mechanistic model to understand the role of different particulate phenomena in the overall behavior observed in the experiment. This required a detailed examination of plasma/fluid behavior in the plasma source section, fluid behavior in the expansion chamber, and mechanisms responsible for particulate generation and growth. The model developed in this work represents the first time integration of these phenomena and was used to simulate mobilization experiments in SIRENS. Comparison of simulation results with experiment observations provides an understanding of the physical mechanisms forming the particulate and indicates if mechanisms other than those in the model were present in the experiment. Key results from this comparison were: the predicted amount of mass mobilized from the source section was generally much lower than that measured, the calculated and measured particle count median diameters were similar at various locations in the expansion chamber, and the measured standard deviations were larger than those predicted by the model. These results implicate that other mechanisms (e.g., mobilization of melted material) in addition to ablation were responsible for mass removal in the source section, a large number of the measured particles were formed by modeled mechanisms of nucleation and growth, and, as indicated by the large measured standard deviations, the larger particles found in the measurement were from an aerosol source not included in the model. From this model, a detailed understanding of the production of primary particles from the interaction of a high energy density plasma and a solid material surface has been achieved. Enhancements to the existing model and improved/extended experimental tests will yield a more sophisticated mechanistic model for particulate production in a fusion reactor.
Date: 2000-04-04
Degree: PhD
Discipline: Nuclear Engineering

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