Understanding radionuclide transport in freshwater systems is critical for assessing radiological risks to humans and ecosystems after a nuclear accident. While existing models often focus on oceanic scenarios, the role of rainfall in riverine environments remains understudied. This research addresses this gap by simulating radionuclide dispersion using HotSpot, CROM, and ERICA tools for a hypothetical accident near a nuclear power plant, incorporating hydrological factors such as rainfall, runoff, and sediment transport

Atmospheric dispersion simulations using HotSpot revealed a 50% increase in ground deposition under rainfall compared to dry conditions, particularly within 1 km of the release site. River transport modeling with CROM showed 20–30% higher radionuclide concentrations during rainfall due to enhanced atmospheric deposition and land-to-river runoff.

Radiation dose assessments for freshwater biota using ERICA indicated exceedances of the 10 µGy·h⁻¹ screening level under rainfall (15.42 µGy·h⁻¹), suggesting ecological risks, while dry conditions remained below thresholds (0.14 µGy·h⁻¹). Human exposure assessments revealed significantly higher doses for infants (7.03 × 10³ mSv/yr) and adults (8.71 × 10² mSv/yr) during rainfall, surpassing ICRP limits (1 mSv/yr), compared to dry scenarios (infants: 4.24 × 10² mSv/yr; adults: 47.5 mSv/yr).

These findings emphasize rainfall’s critical role in radionuclide dynamics, offering insights for improving emergency response strategies and environmental risk assessments near nuclear facilities.