Radiological evaluation of industrial biomass ash: Activity concentration indices and dose assessment to ensure safety in Austria's circular economy

The increasing utilization of biomass for energy production leads to the generation of significant amounts of ash, creating both challenges and opportunities for sustainable management. The objective of this study is to explore the potential application of biomass ash from a radiological perspective in Austria. A total of 51 biomass ash samples, including combustion ashes and gasification residues, were collected from five companies, with sampling sites distributed across Austria. The activity concentrations of ²²⁶Ra, ²³²Th, ⁴⁰K, and ¹³⁷Cs were measured using gamma-ray spectrometry with high-purity germanium detectors, while ⁹⁰Sr was analyzed in seven samples after chemical separation using liquid scintillation counters. A comprehensive understanding of the radionuclides contained in the ash is essential to determine the optimal utilization options. The activity concentration index for gamma radiation emitted by building materials according to the EU Directive 2013/59/EURATOM, as well as extended indices including ¹³⁷Cs, were calculated to determine suitable utilization pathways for the ash in circular economy applications such as cement production and forest fertilization, with different indices ranging from (0.0156 ± 0.0014) to (3.1 ± 0.2). A conservative dose assessment was conducted for a worker handling biomass ash in Austrian industrial plants to evaluate the potential radiation exposure, determined as (0.384 ± 0.073) mSv per year. This value is well below the 1 mSv per year effective dose limit for public exposure, as specified in EU Directive 2013/59/EURATOM, indicating negligible occupational exposure and no radiation protection arrangements deemed necessary.