Investigation of Aerosol Mass and Number Deposition Velocity in a Closed Chamber

In the event of a core disruptive accident in a sodium cooled fast reactor, the Reactor Containment Building (RCB) is bottled-up with coolant (sodium), fuel and fission product aerosols. The aerosols suspended in the closed environment undergo coagulation and gravitational settling. Sodium aerosols are generated by combustion, while fission product aerosols are generated by vaporization and condensation, with the resulting particles having two flow regimes. It is expected that the mass concentration of sodium aerosols is relatively high, on the order of a few g/m3, while that of the fuel and fission products is only a few mg/m3. Taking into account the concentration criteria, experiments are carried out by generating sodium aerosols (mono dispersed) with the concentration of 3.0 g/m3, and the deposition velocity over time is determined by mass measurements (concentration and flux). Similarly, non-radioactive species of SrO2 aerosols are generated (mono dispersed) with a number concentration of 106/cm3, and their deposition velocity over time is determined by number measurements (concentration and flux). The mass deposition velocity of sodium aerosols was found to be more than two orders of magnitude greater than the number deposition velocity of SrO2 aerosols. As the SrO2 aerosols are generated in the free molecular regime, the depletion pattern of the number concentration of suspended aerosols follows a process of simultaneous coagulation and settling. A theoretical formulation for the rate of depletion of the number concentration is developed, and the rate coefficients of coagulation and deposition velocity are determined from the theoretically fitted equation. The experimental and theoretical results are compared and found to be nearly same. The deposition velocity of sodium aerosols is used to predict the deposition time for the suspended aerosol mass concentration inside the RCB. The mass and number deposition velocities are determined by using a state of art Turn Table Instrument fabricated in our lab.