Environmental impact assessments and key factors contribution to uncertainties

During severe nuclear events such as nuclear weapon tests and reactor accidents a major fraction of refractory radionuclides such as uranium and plutonium is present as particles, ranging from sub-microns to fragments and containing a series of actinides, fission and activation products. Radioactive colloids or particles are also released via effluents from reprocessing and reactor facilities, from radioactive dumped waste, from uranium legacy sites as well as during the use of depleted uranium ammunition. Thus, radioactive particles should also be expected in the future when refractory radionuclides are released nuclear sources. Radioactive particles are heterogeneously distributed in the environment, and representative sampling can be difficult to attain, dissolution of particle samples can be incomplete, and subsequently estimated inventories can be underestimated. When radioactive particles enter the environment, weathering processes occur and subsequently associated radionuclides are mobilized. Particle contaminated soils or sediments can therefore act as diffuse sources of radionuclides in the future. Radioactive particles can carry substantial amounts of activity, and act as point sources, providing doses to man and the environment. The mobility, biological uptake and effect of particle-associate radionuclides compared with those existing as ions/molecules have, however, largely been ignored in radiation dosimetry, impact and risk estimates. Therefore, when radioactive particle releases occur, the analytical programme should include techniques providing information on particle characteristics influencing weathering, mobility and biological uptake. An IAEA Coordinated Research Project on Particle Characterization finalized in 2011, and a new CRP on Environmental Behaviour and Potential Biological Impact of Radioactive Particles was launched November 2013. The present paper will present a summary on sources associated with radioactive particle releases to the environment, and focus on particle characteristics of relevance for impact assessment. (authors)