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United States Department of Agriculture

Agricultural Research Service

Title: Modelling Uranium Leaching from Agricultural Soils to Groundwater As a Criterion for Comparison with Complementary Safety Indicators

item Jacques, D - SCK-CEN, MOL, BELGIUM
item Simunek, Jirka - U.C. RIVERSIDE, CA
item Mallants, D - SCK-CEN, MOL, BELGIUM
item Van Genuchten, Martinus

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: November 1, 2005
Publication Date: February 28, 2006
Citation: Jacques, D., Simunek, J., Mallants, D., Van Genuchten, M.T. 2006. Modelling uranium leaching from agricultural soils to groundwater as a criterion for comparison with complementary safety indicators. Book of Abstracts, SCK-CEN meeting, Belgium Nuclear Research Centre, Mol, Belgium. p. 14.

Technical Abstract: Radiological assessments of waste repositories often use the dose to humans as an indicator of safety. There is a tendency, however, to invoke alternative or complementary safety indicators for evaluating and confirming the long-term safety of a repository. One example is the use of concentrations of naturally occurring radionuclides (U, Th) in soils and groundwater. Naturally occurring radionuclides can also end up in soils and groundwater due to human practices, such as application of certain fertilizers in agriculture. Many mineral fertilizers, particularly (super)phosphates, contain small amounts of 238U and 230Th. Field soils that receive P-fertilizers accumulate U and Th and their daughter nuclides, which eventually may leach to groundwater. Our objective was to numerically assess U migration in soils. Calculated uranium fluxes from agricultural fields to groundwater may serve as reference levels for radionuclide fluxes from waste repositories. Calculations were based on a new reactive transport model, HP1, which accounts for interactions between U and organic matter, phosphate, and carbonate. Solid phase interactions were simulated using a surface complexation module. Furthermore, all geochemical processes were coupled with a model accounting for dynamic changes in the soil water content and the water flux. The capabilities of the code in calculating natural U fluxes to groundwater were illustrated using a semi-synthetic 200-year long time series of climatological data for Belgium. Based on an average fertilizer application, the input of phosphate and uranium in the soil was defined. This paper discusses calculated U distributions in the soil profile as well as calculated U fluxeleached fs rom a 100-cm deep soil profile.

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