Challenges associated with the behaviour of radioactive particles in the environment

Abstract

A series of different nuclear sources associated with the nuclear weapon and fuel cycles have contributed to the release of radioactive particles to the environment. Following nuclear weapon tests, safety tests, conventional destruction of weapons, reactor explosions and fires, a major fraction of released refractory radionuclides such as uranium (U) and plutonium (Pu) were present as entities ranging from sub microns to fragments. Furthermore, radioactive particles and colloids have been released from reprocessing facilities and civil reactors, from radioactive waste dumped at sea, and from NORM sites. Thus, whenever refractory radionuclides are released to the environment following nuclear events, radioactive particles should be expected. Results from many years of research have shown that particle characteristics such as elemental composition depend on the source, while characteristics such as particle size distribution, structure, and oxidation state influencing ecosystem transfer depend also on the release scenarios. When radioactive particles are deposited in the environment, weathering processes occur and associated radionuclides are subsequently mobilized, changing the apparent K. Thus, particles retained in soils or sediments are unevenly distributed, and dissolution of radionuclides from particles may be partial. For areas affected by particle contamination, the inventories can therefore be underestimated, and impact and risk assessments may suffer from unacceptable large uncertainties if radioactive particles are ignored. To integrate radioactive particles into environmental impact assessments, key challenges include the linking of particle characteristics to specific sources, to ecosystem transfer, and to uptake and retention in biological systems. To elucidate these issues, the EC-funded COMET and RATE projects and the IAEA Coordinated Research Program on particles have revisited selected contaminated sites and archive samples. This COMET position paper summarizes new knowledge on key sources that have contributed to particle releases, including particle characteristics based on advanced techniques, with emphasis on particle weathering processes as well as on heterogeneities in biological samples to evaluate potential uptake and retention of radioactive particles.

90Sr Content in the Stemwood of Forests within Ukrainian Polissya

“…If the first case (Kyshtym accident), the regional soil conditions cause this difference, while the contrast of our data to the results by Scheglov [13] is a consequence of the lack of 90 Sr 'saturation' in depot biomass compartments of the woody plants. Additionally, the content of 90 Sr is given in a biologically inaccessible form in the matrix of fuel particles during the first period after Chernobyl accident [24,25]. The comparison of various TFs is presented in Figure 4.…”

The nature of Pu-bearing particles from the Maralinga nuclear testing site, Australia

“…Plutonium (Pu)-bearing particles (0.45–2000 µm 1 ) dispersed in the environment as a result of the nuclear fuel cycle, weapons testing and nuclear accidents are generally considered to be refractory and unreactive in their native state, but may be susceptible to chemical weathering and/or physical breakdown 2 . Plutonium can then become mobile and bio-available in water-soluble or particulate forms 3 , resulting in a long-term radiological risk to ecosystems and human health 1 .…”

The retrospective analysis of radionuclides in banded coral from the Bikini Atoll

“…The injected radioactive species (atoms, ions, molecular fragments…etc) are heterogeneously distributed within the local environment. Fate and transport of the radioactive fallout within the surrounding environment depends on particle size, distribution, structure, oxidation state and release scenario (Salbu et al 2018). Radionuclide species are defined in water by their diameters.…”

“…The elemental composition of the radioactive debris depends on the conditions surrounding the formation of the particle. This includes pressure and temperature conditions, construction materials, surrounding infrastructure, local geology, and altitude of the detonation (Salbu et al 2018). Particles can carry substantial amounts of refractory material and settle heterogeneous throughout the bottom of the lagoon.…”