CFD Simulations of Aerosol Dispersion and Agglomeration During the Laser Cutting of Fukushima Fuel Debris Simulants

Abstract

The general context of this article is related to the development of the laser cutting technique for the fuel debris retrieval on the damaged reactors of Fukushima Daiichi. IRSN is involved in a project led by ONET with CEA, to bring relevant elements to analyze the risk occurred by the dispersion of aerosols emitted by the dismantling operations. In this context, CFD (Computational Fluid Dynamics) simulations of dispersion of aerosols (including the transport, the deposition on the walls and the agglomeration), emitted during laser cutting of non-radioactive fuel debris simulants undertaken on the DELIA cutting laser platform from CEA, have been conducted. Indeed, evaluating the amount of aerosols likely to deposit on the walls and those to be released into the environment is one of the key safety issues in the dismantling actions of reactors of Fukushima Daiichi. The CFD simulations have been carried out with the commercial code ANSYS CFX in which models of aerosol transport and deposition, developed and validated by IRSN, have been implemented. In a first time, airflow simulations have allowed to visualize the flow in the vessel of the DELIA laser cutting facility from CEA by the way of streamlines before injecting aerosols. Aerosol input data (size and morphology) have been acquired by IRSN team on the DELIA facility during the laser cutting of non-radioactive simulants of fuel debris for air and underwater configurations. Those simulants of fuel debris are representative of the fuel debris present in the Fukushima reactors [1]. The simulation results allow to obtain the cartography of the aerosol deposition in the vessel for different aerosol sizes and to evaluate the amount of dispersed aerosols. These simulations also show the time evolution of the aerosols properties with the agglomeration phenomena that can influence their size evolution and therefore their dispersion and deposition. Similar simulations have also been carried out on the geometry of a Fukushima Daiichi reactor pedestal in which laser cutting could be performed. This paper presents the aerosol dispersion simulations, the model implemented for aerosol transport and deposition as well as for agglomeration, and finally a comparison with experimental data presented in a companion paper (ICONE26-81531).