Seasonal study of radon concentrations in a uranium mine: A CFD comparison between natural and forced ventilation

• We compared natural and forced ventilation of radon in a former uranium mine. • CFD modeling improved boundary conditions accuracy, raising differences up to 20 • Natural airflow gave only 0.13–0.25 ACH due to inefficient building construction. • Forced ventilation raised ACH up to 2.21, reducing ventilation times. • We confirmed forced ventilation as the most effective mitigation strategy. Radon is a naturally occurring radioactive gas that accumulates inside poorly-ventilated environments, posing significant health risks due to its association with lung cancer. This study analyzes indoor radon dynamics in a building located within a former uranium mine in Saelices el Chico (Spain), evaluating the effectiveness of natural and mechanical ventilation for radon mitigation. Experimental measurements were conducted to monitor radon levels over time, supported by a CFD model that simulated both indoor and outdoor environments while accounting for terrain-induced wind effects. This modeling approach improved boundary condition accuracy, revealing up to 20% discrepancies between raw meteorological data and simulated environments. A seasonal analysis was performed under representative weather conditions and compared with a forced ventilation scenario using an industrial fan to continuously supply fresh air. The mechanical ventilation model showed strong agreement with experimental results. Findings indicate that mechanical ventilation substantially enhances air renewal—reaching up to 2.21 air changes per hour (ACH)—whereas natural ventilation only provides 0.13–0.25 ACH, corresponding to renewal times between 4 and 8 hours. As a result, simulated radon concentrations inside the studied room dropped from over 10,000 Bq/m 3 under natural conditions to about 2,000 Bq/m 3 within just one hour after implementing the mechanical setup. These findings demonstrate the critical role of mechanical ventilation in reducing radon accumulation and improving indoor air quality, particularly in buildings with limited openings, suboptimal airflow paths, or low wind conditions where natural ventilation becomes ineffective.