Screening key site-specific parameters for radiological on-site exposure dose from hypothetical contamination at the planned Ninh Thuan NPP site using the MEPAS module

An on-site radiological exposure dose assessment model was established for a contamination scenario involving 17 radionuclides of concern in the surface soil layer at the planned Ninh Thuan NPP, using the MEPAS module in the FRAMES framework. Exposure dose calculations used two different dose conversion factor (DCF) libraries, including the default MEPAS database and the modified database based on ICRP 107/DCFPAK 3.02, as implemented in RESRAD-ONSITE v7.2. The choice of DCF database significantly affects exposure dose, and the modified DCF database shows closer agreement with the RESRAD-ONSITE result in the early period. A sensitivity analysis was conducted to screen key site-specific parameters, including the thickness of the contaminated zone, the density of surface soil, the fractions and shielding factors of time spent indoors/outdoors, the daily exposure time to external radiation, and the food consumption. For distribution coefficients (K d ) characterizing the transport of radionuclides, lower K d values imply higher mobility through infiltration, faster depletion of radionuclide inventory in the contaminated surface soil layer, and consequently a reduction in on-site exposure dose, and vice versa. The assessment of the impact of climate change in the Ninh Thuan region, forecasted from 2024 to 2104, shows a tendency toward a faster decrease in on-site exposure dose due to a predicted increase in precipitation, which facilitates the mobilization of dissolved radionuclides through water-dependent pathways.