Comparative radiological screening of waste-to-energy and coal-fired-derived bottom ash: a case study from Southern...

This study presents a comparative radiological screening of two types of bottom ash (BA), namely coal-derived and municipal solid waste incineration (MSWI)-derived, generated in Southern Vietnam. A total of 56 BA samples were analysed using low-background gamma-ray spectrometry. Activity concentrations of the ²²⁶Ra and ²³²Th decay series, and ⁴⁰K, were used to derive standard radiological indices and to evaluate Vietnamese regulatory activity concentration indices (I_A3 and I_A4) relevant to outdoor, large-volume, and near-ground reuse scenarios. A probabilistic compliance assessment was conducted to evaluate the derived conventional radiological indices against national regulatory screening criteria. The results show that, for both ash types, measured activity concentrations and derived indices remain below internationally adopted screening reference levels for external gamma exposure (Ra_eq- and H_ex/H_in-based criteria), with coal-derived BA exhibiting systematically higher values and greater variability than MSWI-derived BA. Per-sample deterministic screening based on measured point estimates indicates compliance with applicable screening criteria across almost all samples, while probabilistic compliance analysis based on Monte Carlo uncertainty propagation reveals a low likelihood of exceeding the relevant screening thresholds, particularly for MSWI-derived BA. By explicitly linking measured radionuclide inventories to tiered national screening indices and uncertainty-aware compliance metrics, this study provides a transparent framework for radiological screening of BA reuse under emerging waste-to-energy contexts. Within the scope of external gamma exposure considered, the findings suggest that controlled reuse may be feasible at a first-tier screening level from a radiological perspective only for BA in outdoor earthwork applications, while highlighting the need for complementary assessments of non-radiological hazards.