Measurements of Charged Aerosol Coagulation

In high-temperature gas-cooled reactors (HTGRs), an improved understanding of the production of carbonaceous dust (e.g., by abrasion, corrosion, radiation damage, and gas-to-particle conversion) and the subsequent transport of the dust and associated sorbed fission products is needed. Diffusion charging and/or self-charging of the suspended dust particles (aerosol) is likely to occur, which affects how the aerosol evolves in time and ultimately deposits on surfaces. At present, nuclear reactor safety codes, such as MELCOR, do not account for these effects and there is currently no consensus on their importance, partly due to a lack of experimental data as well as tools for computations. Further experimentation and modeling of these effects are therefore needed to resolve these issues. We report on an experimental investigation of the coagulation of charged aerosols pertinent to HTGRs by measuring the evolution of size and charge distributions over time and comparing the experimental results with computations using the direct simulation Monte Carlo method. Measurements have been completed for both silver and carbon ultrafine aerosols using a tandem differential mobility analyzer and an open-flow coagulation chamber with a residence time of nearly 400 s. Results for both aerosols indicate that coagulation occurs faster than predicted by the simulations, at times differing by an order of magnitude. While the paper is focused on specific aerosols, it is of wider significance in that it provides the first such comparisons between data and simulations on charged aerosol coagulation.