Modeling of atmospheric dispersion of sodium fire aerosols for environmental impact analysis during accidental leaks

In this study a chemical kinetic model which converts sodium oxide aerosols to sodium carbonate aerosols as a function of CO2 and humidity is implemented in the FLEXPART atmospheric dispersion model for impact assessment during sodium fire accidents in sodium cooled fast reactors. The model is validated with open environment aerosol dispersion experiments conducted at Kalpakkam coastal site. Simulated total aerosol concentrations and deposition agree with experimental data. Simulations indicate rapid conversion of NaOH to Na2CO3 during atmospheric transport under high humidity levels (57-80%) at Kalpakkam. Parametric tests with different particle size indicated that a particle diameter of 5 mu m produced realistic aerosol deposition closely comparing with observations. A series of simulations were conducted for various meteorological conditions to assess the chemical impact in a range of 25 km during a postulated accident. Simulations for extended 8-h release scenarios in different seasonal flow conditions indicate the concentrations beyond 1.5 km fall to very low values (<= 0.1 mg/m(3) for NaOH and <= 4 mg/m(3) for Na2CO3) indicating no chemical impact. Short-duration (1 h) releases during worst environmental conditions (sea breeze, low winds) indicate that the aerosol concentrations during sea breeze are about 4-5 times high compared to winter time calm winds due to wide diffusion of aerosols in winter. The concentrations in these two cases are found to be higher (similar to 0.2 mg/m(3) for NaOH and 6 mg/m(3) for Na2CO3) in the site distance range but thereafter rapidly fall, thus indicating no inhalation hazard during sodium fire scenarios at the coastal site.