Numerical Simulation of Aerosol Generation and Aerosol Spray Scavenging During Fukushima Daiichi Decommissioning

In the future decommissioning plan of the damaged Fukushima Daiichi nuclear reactors, the melted and re-solidified fuel debris at the bottom of the reactor pressure vessel and primary containment vessel will be cut into small pieces before retrieving them from reactor buildings. Submicron aerosol particles that generated during cutting operations must be removed inside the containment vessel before they escape to the environment. The existed spray system inside the containment vessel can be used to remove these aerosol particles under different collection mechanisms. In this study, a new numerical model is developed to simulate both the aerosol generation by cutting fuel debris and aerosol removal by spray injection in the open-source CFD code OpenFOAM using the geometry of our model facility (UTARTS facility). Simulation results provide detailed information about the time evolution of aerosol distribution, and also show that aerosol generation rate has no influence on aerosol removal efficiency, and larger particles can be removed faster because of stronger inertial impaction. The newly developed numerical model with considering both aerosol generation due to cut fuel debris and aerosol scavenging by spray droplets can be used in the real-size containment vessel of Fukushima Daiichi nuclear reactors to optimize the design of future spray systems.