Baseline Evaluation of Natural Radioactivity and Radiological Risk in River Sediments

Abstract

This study establishes baseline activity concentrations of natural radionuclides (Ra-226, Th-232, and K-40) in pre-operational river sediments near Indonesia’s first nuclear power plant (NPP). It evaluates associated radiological health risks related to their potential use as building materials. Sixteen sediment samples were collected along an upstream–downstream transect of the Raya River, Bengkayang Regency, West Kalimantan, and analyzed using HPGe gamma spectrometry. Radiological hazard indices (Raeq, Hex, Hin, absorbed dose rate, and annual effective dose) were assessed following UNSCEAR and IAEA guidelines. Spatial analysis showed localized radionuclide enrichment in midstream areas with decreasing concentrations downstream. Activity concentrations ranged from 35.18–80.31 Bq/kg for Ra-226, 25.15–108.49 Bq/kg for Th-232, and 288.38–781.56 Bq/kg for K-40. Although the mean absorbed dose rate (82.37 nGy/h) exceeded the global average, all mean hazard indices (Raeq: 178.06 Bq/kg; Hex: 0.48; Hin: 0.64; AED: 0.10 mSv/y) remained below international safety limits. Overall, the study establishes a robust pre-operational radiological baseline that will facilitate future impact assessments and regulatory monitoring during the operational phases of nuclear development.