Following releases from severe nuclear events such as nuclear weapon tests, use of depleted uranium ammunition and reactor explosions or fire, a major fraction of refractory radionuclides such as uranium (U) and plutonium (Pu) is present as particles, often ranging from submicrons to fragments. Radioactive particles and colloids are also released via effluents from reprocessing facilities and civil reactors, and radioactive particles are identified in sediments in the close vicinity of radioactive waste dumped at sea. Thus, releases of radioactive particles containing refractory radionuclides should also be expected following severe nuclear events in the future.
Radioactive particles in the environment are heterogeneously distributed and can carry substantial amounts of refractory fission products, activation products and transuranics. Samples collected may not be representative and inert particles can be difficult to dissolve. For particle contaminated areas, the estimated inventories can therefore be underestimated. As particle weathering and remobilisation of associated radionuclides will occur over time, these entities represent diffuse sources for future ecosystem transfer. Thus, analytical techniques providing information on particle characteristics such as size distributions, crystallographic structures, oxidation states, being variables influencing weathering, mobility and biological uptake, is essential for impact and risk assessment. The present paper summarizes present documented knowledge on sources that have contributed to radioactive particles in the environment.