Journal of Nuclear Fuel Cycle and Waste Technology

To characterize quantitatively the transport of 99Tc and the global fallout (137Cs, 90Sr, and 239+240Pu) for soils in Korea, the transport parameters of a convective-dispersion model, apparent migration velocity, and apparent dispersion coefficient were estimated from the vertical depth profiles of the radionuclides in soils. The vertical profiles of 99Tc were measured from a pot experiment for paddy soil that had been sampled from a rice-field around the Gyeongju radioactive waste repository in Korea, and the vertical depth distributions of the global fallout 137Cs, 90Sr, and 239+240Pu were measured from the soil samples that were taken from local areas in Korea. The front edge of the 99Tc profiles reached a depth of about 12 cm in 138 days, indicating a faster movement than the fallout radionuclides. A weak adsorption of 99Tc on the soil particles by the formation of Tc(VII) and a high water infiltration velocity seemed to have controlled the migration of 99Tc. The apparent migration velocity and dispersion coefficient of 99Tc for the disturbed paddy soil were 2.88 cm/y and 6.3 cm2/y, respectively. The majority of the global fallout 137Cs, 90Sr, and 239+240Pu were found in the top 20 cm of the soils even after a transport of about 30 years. The transport parameters for the global fallout radionuclides were 0.01-0.1cm/y (137Cs), 0.09- 0.13cm/y (90Sr), and 0.09-0.18cm/y (239+240Pu) for the apparent migration velocity: 0.21-1.09 cm2/y (137Cs), 0.12- 0.7cm2/y (90Sr), and 0.09-0.36cm2/y (239+240Pu) for the apparent dispersion coefficient.

Keywords

Transport in soil,Convective-dispersion model,Migration velocity,Dispersion coefficient