Laboratory experiments to characterize radiochloride diffusion in unsaturated soils

Area of Science:

• Environmental Science
• Soil Science
• Radiochemistry

Background:

• Understanding radionuclide transport in soils is crucial for environmental safety.
• Chloride-36 (36Cl) is a non-reactive radionuclide relevant to nuclear waste disposal and environmental monitoring.
• Soil properties and experimental conditions influence radionuclide diffusion and sorption.

Purpose of the Study:

• To investigate the diffusion transport of 36Cl in unsaturated soils.
• To determine the influence of soil properties and packing conditions on 36Cl apparent diffusion coefficients (D(a)).
• To compare solid-liquid distribution coefficients (K(d)) derived from diffusion experiments with batch experiments.

Main Methods:

• Diffusion experiments using packed soil columns with varying 36Cl activity.
• Analysis of 36Cl diffusion profiles to calculate apparent diffusion coefficients (D(a)).
• Calculation of solid-liquid distribution coefficients (K(d)) from D(a) and comparison with batch K(d) values.

Main Results:

• Apparent diffusion coefficients (D(a)) for 36Cl ranged narrowly (3-7x10(-10) m(2) s(-1)), indicating minimal influence of soil properties.
• Soil packing conditions significantly affected 36Cl diffusion.
• Distribution coefficients (K(d)) from diffusion were lower than batch K(d) values, suggesting negligible radiochloride-soil interaction.

Conclusions:

• Soil packing density is a more critical factor than soil properties for 36Cl diffusion under unsaturated conditions.
• The low K(d) values confirm minimal sorption of chloride onto soil, consistent with its non-reactive nature.
• Findings are relevant for predicting the environmental fate and transport of chloride and similar radionuclides.