Modelling the ingress and charge enhanced deposition behaviour of radioactive aerosols in dwellings

Radioactive aerosols of accidental origin can travel long distances once airborne and although dwellings can provide some shelter, ingressed radioactive aerosol has been shown to be injurious to human health. Modelling approaches have been widely used to study indoor aerosol behaviour, but such approaches have not to date considered the self-charging nature of radioactive aerosol and the consequent effect upon aerosol deposition. In this work, a multi-zone modeling tool is used to simulate indoor aerosol concentrations in the individual rooms of a bungalow and semi-detached dwelling, for three radioactive aerosol particles sizes (0.5, 1.0, 2.0 mu m, with aerosol deposition enhancement due to particle charge), two plume types (5 h and 24 h), and a range of representative dwelling airflow conditions (low air flow LAF and high air flow HAF1), including mechanical extract ventilation (HAF2). When comparing the time series of aerosol concentrations in different rooms, lower concentrations of charged aerosol, relative to uncharged, were observed, suggesting charge-enhanced deposition, and this phenomena is more striking during a 24 h plume compared to 5 h plume, where the difference between the two is up to 50% in one of the zones of the dwelling. The concentration comparison of charged aerosols concentration between LAF and HAF1 cases also showed that during a 5 h plume, the aerosol concentration is twice as high for the HAF1 case. These simulation results demonstrate that the effect of charged-enhanced aerosol deposition should be considered when assessing the benefits of sheltering in a building in the event of a nuclear accident.