Characterisation of aerosols produced in a simulated severe nuclear accident using electron microscopy

- Radioactive fission products were condensed and sampled for electron microscopy.
- Caesium-Rhenium particles and agglomerates of those were observed.
- Unlike in thermodynamic-equilibrium calculations, no caesium molybdate was observed.
- Caesium molybdate particles only in hydrogen and above 1073 K.

The chemical composition of aerosols formed by revaporisation and subsequent condensation of fission products and simulant material was investigated using electron microscopy. A stage dedicated only to the collection of aerosol particles on carbon coated copper grids was designed and tested. As raw material for these experiments core material from the TMI-2 accident, fission product deposits from the Phébus FPT3 tests and Cs2MoO4 powder were used. The examination of aerosols was made by transmission and scanning electron microscopy and energy-dispersive X-ray spectroscopy. The results indicate the range of species encountered at different temperatures showed the necessity for a time dependent sampling method. The investigated aerosols were in the nanoparticle range. A clear pattern was found for the use of fission product deposits from the Phébus FPT3 experiments. In oxidising atmosphere in the temperature range of 450 K to 910 K a species of 2 nm sized spherical caesium-rhenium particles were observed that coagulated to spherical about 20 nm sized particles. Other elements such as Mo and Te occurred at various temperature ranges and atmospheres. Also the vaporisation of caesium molybdate, as predicted in thermodynamic equilibrium calculations, was examined.