Radioactive Particles released from various Nuclear Sources

Radionuclides released tot the environment may be present in different physico-chemical forms, ranging from ionic species to colloids, particles and fragments. Following releases during nuclear events such as nuclear weapon tests or use of depleted uranium munitions, and from nuclear accidents associated with explosions or fires, radionuclides such as uranium and plutonium are predominantly present as particles, mainly fuel particles. Similarly, radioactive particles are present in effluents from reprocessing facilities, and radioactive particles are observed in sediments in the close vicinity of radioactive waste dumped at sea. Thus, releases of radioactive particles occur more often than earlier anticipated. Soil and sediments can act as a sink for colloids, particles and fragments, while contaminated soil/sediments may also act as a potential diffuse source, depending on particle characteristics and processes influencing particle weathering and mobilisation of associated radionuclides. To assess long-term impact from radioactive particle contamination, information on the source term is essential, i.e. activity concentrations and isotopic ratios as well as the particle size distribution, crystallographic structures and oxidation states influencing particle weathering rates and the subsequent mobilisation and biological uptake of associated radionuclides. The activity concentrations and the isotopic ratios will be source dependant, while particle characteristics will also reflect the release scenario, dispersion processes and deposition conditions. The present paper will summarise present knowledge on radioactive particles released from various nuclear sources and differences in particle characteristics observed when using advanced techniques such as electron microscopy and synchrotron radiation based X-ray micro-techniques. (author)