Simulation of the concentrations and distributions of indoor radon and thoron

The technique of computational fluid dynamics (CFD) was used to study the concentrations and distributions of indoor radon (Rn-222) and thoron (Rn-220) as well as their progeny in three dimensions. According to the simulation results, in a naturally ventilated room, the activity distribution of Rn-222 is homogeneous except for the places near air diffuser (supply and exhaust) locations. The concentration of Rn-220 exponentially decreases with the distance from the source wan which is considered independently. However, as the ventilation rate increased, the concentrations of both Rn-222 and Rn-220 decreased and their activity distributions become complicated due to the effect of turbulent dow. It suggests that the impact factors of monitoring conditions (sampling site, airflow characteristics, etc.) should be taken into account in obtaining representative concentrations of Rn-222/Rn-220 for dose assessment Both the simulation results of activities and their distributions agreed well with the experimental results in a laboratory room. It suggests that the CFD models may be applicable for the estimation of indoor Rn-222 and Rn-220 as well as their progeny.