Experimental and numerical study on aerosol mass concentration attenuation in reactor containment during LBB events

Under Leak-Before-Break (LBB) accident conditions, containment ventilation systems can operate under elevated air exchange conditions, introducing forced convection that modifies aerosol transport behavior. Large internal structures in engineering-scale compartments further disturb the flow field and generate spatially heterogeneous flow and turbulence structures. Many existing aerosol attenuation and deposition models were developed and validated either for sealed, quiescent environments dominated by natural convection, or for obstacle-free chambers under low-to-moderate ventilation rates. Their applicability to LBB-relevant conditions therefore remains uncertain. This study investigates aerosol attenuation in a mechanically ventilated compartment with representative nuclear-island obstacle layouts at an air change rate of 12 h −1 , intended to represent compact containment layouts adopted in integral pressurized water reactor and small modular reactor concepts. Experiments were combined with numerical simulations comparing an Eulerian approach incorporating the Lai–Nazaroff deposition formulation and a Lagrangian Discrete Phase Model with Discrete Random Walk (DPM–DRW) framework. The measured average total aerosol removal rate was 25.4 h −1 , of which deposition contributed 13.4 h −1 . This deposition component exceeds values commonly reported under conventional indoor ventilation conditions and is comparable to the ventilation removal contribution. When coupled with a near-wall-resolving turbulence closure—specifically the Shear Stress Transport (SST) k–ω model—the DPM–DRW framework reproduced the observed attenuation trend with a predicted decay coefficient of 22.8 h −1 , within 10.2% of the measured 25.4 h −1 . By contrast, wall-function-based models (realizable k–ε) overpredicted removal by over a factor of two, while both the well-mixed single-zone model and the Lai–Nazaroff formulation systematically underestimated deposition-associated attenuation under the present geometric and flow conditions. These results indicate that deposition may remain an important removal mechanism even under elevated ventilation conditions in compactly arranged containment compartments. The findings suggest that conventional ventilation-dominated attenuation assumptions do not fully capture aerosol removal under the present conditions, and that deposition should therefore be considered when selecting an aerosol attenuation model for such compact configurations.