Utilizing cerium as a surrogate for actinide aerosols: Real-time characterization and formation mechanisms in nuclear...

Characterizing radioactive aerosol particles released from actinide metals on fires represents a pivotal process in nuclear emergency response. However, the precise characterization of these particles and the deep understanding of their formation mechanism remain a daunting challenge due to the lack of in-situ measurement techniques. We presented the first real-time investigation of respirable particles with the size ranging from 2 nm to 10 μm, emitted from the combustion of cerium metal (CM) as surrogate for actinide counterparts. The evolution of such particles was revealed by the methodology combining scanning mobility particle sizer and optical particle sizer, showing the consistent generation of multimodal ultrafine particles with diameters of 2-100 nm during the combustion reaction. Numerous polydisperse 0.2-0.5 μm accumulated particles and a few 2-10 μm coarse particles were also produced via droplet dispersion and explosion during molten CM self-enhanced combustion. These particles were predominantly composed of CeO₂ and exhibited lognormal distributions. The spherical, aggregated, chain-like and fractured particles implied the evolution of particles including nucleation, coagulation, agglomeration and oxide layer cracking. Comparative analyses of particle size distributions reveal that bulk CM combustion predominantly generated ultrafine particles in the absence of CM droplet dispersion. Our finding will guide a critical evaluation of respirable actinide aerosols in the case of fire accidents involving actinide metals.