Migration of radionuclides through

A number of methods have been proposed for predicting the migration of radionuclides through the soil. Most methods have used a concept of layers of soil, one upon another, with the radionuclide migrating from the top layer downward. 

For more than one decade now, a large number of EC coordinated projects have been performed imder the umbrella of the international coordinated project MIRAGE (Migration of RAdionuclides through the GEosphere), and a recently performed review study on the project MIRAGE aimed to come to a critical evaluation of the state-of-the-art in the different research areas of the project and to evaluate how the results obtained contribute to rqKjsitory perfonnance/safety assessment. The study focused on the three main research areas of that project such as ... 

Retention the migration of radionuclides through the technical barrier system and the geosphere is characterized by various retention or retardation processes such as chemical adsorption, ion exchange, precipitation, chemical interactions, molecular filtration, dispersion and diffusion. This causes the nuclide velocity to be lower than the groundwater velocity. 

Read, D., Ross, D. Sims, R. J. 1998. The migration of uranium through clashach sandstone The role of low molecular weight organics in enhancing radionuclide transport. Journal of Contaminant Hydrology, 35, 235 -248. 

The groundwater transport of radionuclides through waterbearing interbed layers in the Columbia River basalt formation will be controlled by reactions of the radionuclides with groundwater and interbed solids. These interactions must be understood to predict possible migration of radionuclides from a proposed radioactive waste repository in basalt. Precipitation and sorption on interbed solids are the principle reactions that retard radionuclide movement in the interbeds. The objective of the work described herein was to determine the sorption and desorption behavior of radionuclides important to safety assessment of a high-level radioactive waste repository in Columbia River basalt. The effects of groundwater composition, redox potential, radionuclide concentration, and temperature on these reactions were determined. 

Besides the composition of the soils, other factors have a major influence on the migration of radionuclides rainfall, the thickness of the soil layers, their permeability to water, and the nature of the layers underneath. For example, Cs is washed down quickly through layers of sand, but it will stay in layers of clay. Pu is sorbed by clay more strongly than by sand and may stay in soils for rather long times, if it is not dissolved by complexation or displaced by other compounds. 

Lester, D.H., Jansen, G., and Burkholder, H.C., Migration of Radionuclide Chains Through an Adsorbing Medium, BNWL-SA-5079, Battelle Pacific Northwest Laboratories, Richland, WA, December 1974. 

When radionuclides are stored as wastes either in permanent repositories or in waste storage areas the possibility of escape into the environment must be considered. This escape may result in airborne contamination or in contamination of environmental surfaces. This paper will not concern itself with airborne contamination but rather with the surface contamination and the transport and migration of radionuclides into the lithosphere through the agency of water. 

This computational model calculates the annual radiological dose to humans over geological time scales due to the underground migration of radionuclides from a hypothetical nuclear waste disposal site through a system of idealised natural and engineered barriers. 

Artificial radionuclides in bottom sediments of the Don River Estuary-Azov Sea (Black Sea) were measured to examine the storage and migration of radionuclides within this inland sea and to estimate the annual dose received by individuals in the local population who regularly consume fish (Matishov et al. 2002). The specific activity of surface sediments was 0.5—100 Bq/kg dry wt. [mean = (33.8 25.9) Bq/kg dry wt., the number of samples = 57] for Cs, 0.2-5.7 Bq/kg dry wt. [mean= (2.1 1.4) Bq/kg dry wt., the number of samples = 34] for Sr and 0.31-0.51 Bq/kg dry wt. (the number of samples = 2) for Pu in 1997—1999. Cs specific activities increase with distance from the mouth of the Don River and correlate negatively with the sediment grain size (square of the correlation coefficient, / = 0.77, the number of data points, n = 21). The annual Cs-derived dose received by an individual through the tropic chain water—fish-humans (approximately 10 Sv/a) is well below regulatory recommended limits. 

The principal mechanisms which are mling the migration of radionuclides firom the repository through its near field and far field back to the biosphere are related to two fundamental categories of processes in the geosphere which need to be understood and modelled ... 

Data from these loos indicate that verv low concentrations of radionuclides such as Xo, Xs, "Sb, and Ru were present in Well 199-N-9 soils above the water table, although the concentration increases markedly in soils at the water table. Wells 199-N-12 and 199-N-13 are more distant from the trench and had lower radionuclide concentrations in the unsaturated zone but also had elevated concentrations at the water table (within the saturated zone). These data indicate that extensive lateral migration of contaminants from the trench within the unsaturated zone is not apparent in these borings (DOE-RL 1990). Mechanisms that control the lateral migration of contaminants through the unsaturated zone include dispersion, diffusion, capillary flow, migration through a low-permeability zone because of increased moisture content and perched water, and the adsorption capacity of the soil. 

Similarly, the methodologies implemented in state-of-the-art models for predicting the physical processes of radionuclide migration through the aquatic environment are not discussed here. A review of the methodologies, including transport due to water currents, diffusion, settling, and resuspension has recently been published by Monte et al., where the models are briefly described, model parameter values reviewed, and values recommended (Montea et al. 2009). 

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