Study on Aerosol Deposition Characteristics of an Obstacle Structure During Ventilation for Fukushima Daiichi Decommissioning

Aerosol generation and transport during fuel debris retrieval pose critical challenges for radiological safety in Fukushima Daiichi decommissioning. In particular, the deposition of radioactive aerosols on structural obstacles within the primary containment vessel can strongly influence contamination pathways under low-velocity ventilation. This study experimentally investigates aerosol deposition behavior in the presence of a simplified cube obstacle under laminar ventilation flow using zirconia aerosols as simulants.The flow resistance measurements revealed that, in laminar conditions, the overall pressure losses were dominated by viscous wall shear rather than obstacle-induced form losses. Nonetheless, localized flow stagnation and recirculation zones around the obstacle promoted aerosol deposition. The particle size distributions measured upstream and downstream indicated preferential depletion of larger particles (>0.4 μm), consistent with deposition dominated by gravitational settling, while finer aerosol particles remained deposited mainly by diffusion.Mass and morphological analyses confirmed that deposition was consistently higher on the top horizontal surface than on the vertical sides, highlighting the governing role of gravity and flow recirculation in enhancing aerosol deposition. These findings provide fundamental insights into aerosol deposition processes under ventilation operations and offer practical guidance for predicting contamination hot spots and designing effective decontamination strategies for Fukushima Daiichi decommissioning.