Radionuclide Behavior in Soils and Soil-to-Plant Concentration Ratios for Assessing Food Chain Pathways(NUREG/CR-7120, PNNL-20979)

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Publication Information

Manuscript Completed: November 2011
Date Published: March 2012

Prepared by:
B. A. Napier
R. J. Fellows
K. M. Krupka

Pacific Northwest National Laboratory
P.O. Box 999
Richland, WA 99352

P. R. Reed, NRC Project Manager

NRC Job Code N6455

Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington DC 20555-0001

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Abstract

This report describes work performed under the U.S. Nuclear Regulatory Commission’s (NRC’s) project Radionuclide Uptake in Plants and Animals for Food-Chain Pathway Analyses in Biosphere Models. The project was established by the NRC to assess and evaluate a number of key parameters used in the food-chain models employed in performance assessments of radioactive waste disposal facilities. Section 1 of this report gives the objectives and a brief overview of the report’s organization. Section 2 summarizes characteristics of samples of soils and groundwater from three geographical regions of the United States, the Southeast, Northwest, and Southwest, and analyses performed to characterize their physical and chemical properties. Section 3 discusses physicochemical speciation and geochemistry of radionuclides in these natural soil-water systems. Because the uptake and behavior of radionuclides in plant roots, plant leaves, and animal products depends on the chemistry of the water and soil coming in contact with plants and animals, water and soil samples collected from these regions of the United States were used in experiments at Pacific Northwest National Laboratory to determine radionuclide soil-to-plant concentration ratios. Section 4 describes how crops and forage used in the experiments were grown in the soils, and long-lived radionuclides introduced into the groundwater provide the contaminated water used to water the grown plants. The radionuclides evaluated include neptunium-237 and iodine-125. Plant varieties include alfalfa, corn, and potato. The radionuclide uptake results from this research study show how regional variations in water quality and soil chemistry affect radionuclide uptake. Section 4 summarizes the procedures and results of the uptake experiments, and relates the soil-to-plant uptake factors derived. In Section 5, the results found in this study are compared with similar values found in the biosphere modeling literature; the study’s results are generally in line with current literature, but soil- and plant-specific differences are noticeable. This food-chain pathway data may be used by the NRC staff to assess dose to persons in the reference biosphere (e.g., persons who live and work in an area potentially affected by radionuclide releases) of waste disposal facilities and decommissioning sites.