Simulation of indoor radon and ventilation systems in a scale model room to assess the contribution of high activity building materials to indoor radon.

Indoor radon accumulation is considered the main source of human exposition to ionizing radiation. The main sources of indoor radon are soil gas, the building materials and tap water, especially when they are enriched in ²²⁶Ra and ²³²Th, which are the precursors of main radon isotopes: ²²²Rn and ²²⁰Rn, respectively.

In the frame of RESPIRE (Radon rEal time monitoring System and Proactive Indoor Remediation), a LIFE project funded by European Commission, a scale model-room of 62 cm x 50 cm x 35 cm (inner length x width x height) was manufactured with a very porous and highly radioactive lithoid ignimbrite to evaluate the contribution of building materials to indoor radon accumulation, simulating the effect of a ventilation system to reduce indoor radon levels.

A series of experiments was designed where either outdoor air was introduced in the model room or indoor air was extracted from the room, at different flow rates (from 0.15 to 0.82 liters per minute) to evaluate how air exchange and mixing affect indoor radon level. In the first group of tests, the introduction of outdoor air strongly reduced indoor radon concentration, with radon relative decrease directly proportional to the air flow. In the second set of experiments, the extraction of indoor air very moderately lowered radon levels. Finally, a modified version of Fick’s second law was used to model experimental data, describing how radon diffused through the very porous room walls under different experimental conditions.