Experimental Study on the Behavior of Suspended Aerosols of Sodium and Nonradioactive Fission Products (SrO₂ and CeO₂) in a Closed Vessel

In core disruptive accident conditions of sodium-cooled fast reactors, the reactor containment building (RCB) is filled with a large amount of sodium aerosols, along with fuel and fission product aerosols. The environmental source term depends on the quantity of aerosols released from RCB, which in turn depends on the quantity of aerosols that remains suspended in the RCB volume. The sodium aerosols are generated by the combustion process, resulting in micrometer-sized aerosols, while fuel and fission product aerosols are generated by vaporization condensation, resulting in nanometer-sized aerosols. To ascertain the behavior of mixed aerosols generated by the different processes, experiments are conducted by generating sodium aerosols and nonradioactive fission product aerosols and then studying their behavior in a closed vessel. The study includes (a) the initial size distribution of CeO₂ and SrO₂ aerosols, (b) the behavior of suspended mass concentration as a function of time, and (c) the behavior of suspended number concentration as a function of time. The initial size of the sodium combustion aerosols is [approximately]1.0 m, whereas the initial size of the fuel and fission product aerosols is nanometer sized ([approximately]30 nm). In the context of the behavior of the two different-sized aerosols, sodium aerosol behavior dominates the overall suspended mass concentration of the system. The rate of change of number concentration exhibits two regions. The timescale involved for the Brownian coagulation region is found to be [approximately]80 min for nonradioactive fission product aerosols, whereas it lasts only 20 to 30 min when the aerosol system is mixed with sodium aerosols.