Calculation of the Increase in Dose Rate Due to Precipitation at the Bilbao Radiological Station of the Basque...

The Radiological Surveillance Network of the Autonomous Community of the Basque Country continuously monitors environmental dose rate levels to detect potential radiological anomalies. However, during rainfall events, increases in dose rate that occasionally exceed predefined alarm thresholds have been observed, despite the absence of radiological incidents. This study presents a predictive model to estimate the increase in dose rate caused by precipitation events at the Bilbao monitoring station. The model accounts for the atmospheric scavenging of radon progeny by raindrops and their subsequent deposition on horizontal surfaces surrounding the detector. Atmospheric transport, radioactive decay, washout processes, and rainwater accumulation dynamics are incorporated into the formulation. The model is implemented numerically using a finite-difference scheme and validated against experimental measurements from the monitoring station. The results (correlation coefficient, BIAS, RMSE) show good agreement between calculated and measured dose rate increases during precipitation episodes, indicating that the observed variations are mainly attributable to the deposition of short-lived radon progeny.