Characterization and mitigation of radioactive dust during graphite retrieval process of nuclear decommissioning

During graphite retrieval in nuclear decommissioning, radioactive dust can be generated, posing challenges for radiation protection and environmental safety. However, the physicochemical properties and mitigation strategies for graphite dust remain poorly characterized, causing uncertainties to its safe handling and containment. This study investigated aerosol generation during graphite retrieval operations of the experimental shielding reactor in Tsinghua University, focusing on both block removal and drilling procedures. A field-scale experimental setup was implemented, including optical particle counters (OPCs), a scanning mobility particle sizer (SMPS), and aerosol samplers to characterize the particle size distribution, morphology, and radioactivity of both airborne and deposited graphite dust. Results showed that the released particulates were predominantly micrometer-sized, with PM₁₀ concentrations over 160 μg/m³ during drilling for powdered samples. However, the use of an on-site high-flow ventilation system (3300 m³/h) achieved a mitigation efficiency of over 90 %, effectively limiting aerosol dispersion. The radioactivity of aerosols collected by filter membranes was therefore relatively low (α: 0.40-0.48 mBq/m³; β: 3.37-4.89 mBq/m³). Additionally, the dust extractor at the source further suppressed the release of coarse particulates. This study provides practical data and strategies for radioactive graphite dust control during retrieval, which can improve operational safety and radiological protection in nuclear decommissioning.