TRANSPORT OF LOW-LEVEL RADIOACTIVE SOIL AT DEEP-OCEAN DISPOSAL SITE

Transport studies were conducted to assess ocean disposal of soil contaminated with low-level natural radioisotopes. The experimental approach involved characterization of the soil for parameters affecting transport and fate of radionuclides. Radioactivity was associated with discrete soil particles up to 6,000-mu-m. Gross and most individual isotope and element activities were more concentrated on smaller particles. The median size based on gross radio-activity was 125-mu-m, while the median size based on dry mass was 350-mu-m. Particle-settling velocities measured in a 1 m settling column ranged up to 8.2 cm/s (median 2.1 cm/s). Large-scale mixed water column experiments (5 m) confirmed that settling would be the dominant verticle transport mechanism for the soil particles. Experimental results were used to calibrate a convective-diffusive transport model, which was applied to a hypothetical ocean disposal site in 4,000 m of water. The model indicated that 95% of the soil and associated radionuclides would impact the bottom sediment within five days and up to 40 km from the disposal point, along the mean current flow.