Understanding radon behaviour in traditional Indian dwellings: Insights from a validated CFD study of a representative mud test house.

Understanding radon and its short-lived progeny in households is essential for reliable exposure and dose estimation as well as for developing effective mitigation strategies. Typical Indian dwellings, often constructed using local materials and relying on passive ventilation, pose unique challenges for such assessments. In this study, a phased approach was adopted: a full-scale mud test house representative of Indian dwellings was constructed, in-situ measurements of radon and progeny were conducted, Computational Fluid Dynamics (CFD) simulations were performed, and the model outcomes were validated against both experiments and an analytical room model. The validated modeling framework revealed pronounced spatial non-uniformity, with the maximum and minimum concentrations of radon and progeny varying by an order of magnitude. This heterogeneity underscores the limitations of well-mixed room models and highlights the added value of CFD in exposure assessment. Simulations further showed that ventilation strongly governs exposure levels, with an increase from 0.5 to 25 Air Changes per Hour (ACH) reducing radon concentrations by more than 90 % (from ∼350 to ∼22 Bq m-3) and progeny concentrations from over ∼90 to ∼1 Bq m-3.