Numerical simulation of aerosol generation by cutting fuel debris and aerosol removal by spray droplets during Fukushima decommissioning

The proposed plan for decommissioning the damaged Fukushima Daiichi nuclear reactors involves cutting the melted and re-solidified fuel debris into small pieces for retrieval from the reactor buildings. However, the cutting process generates submicron aerosol particles that need to be removed from the containment vessel before they escape into the environment. The existing spray system inside the containment vessel can be used to remove these aerosol particles using various collection mechanisms. To simulate both the aerosol generation and removal processes, a new numerical model has been developed using the open-source Computational Fluid Dynamics code OpenFOAM. The simulation results indicate that the rate of aerosol generation does not affect the efficiency of aerosol removal, and larger particles can be removed faster due to stronger inertial impaction. The newly developed numerical model has also been used to simulate aerosol generation and removal in the real-size containment vessel of Fukushima Daiichi nuclear reactor unit 3. The simulation results provide information on the spatial distribution of aerosol particles under different multiple-nozzle layouts, which can be used to optimize the design of future multiple-nozzle spray systems for the real Fukushima decommissioning.