Sources, vertical distribution, and migration rates of 239,240Pu, 238Pu, and 137Cs in grassland soil in three localities of central Bohemia

The vertical distribution and sources of Pu-239,Pu-240, Pu-238 and Cs-137 were determined at three sites in undisturbed grassland soils. Using a compartment model, the migration rates of Pu-239,Pu-240 Originating from atmospheric nuclear tests and Chernobyl-derived Cs-137 in soil were calculated for widely used convection and as well for diffusion transport processes. Deposition of small amounts of Chernobyl-derived plutonium (0.5-1.0 Bq m(-2) Pu-238 and 1-2 Bq m(-2) Pu-239,Pu-240) was found at two sites. The migration rate of Pu-239,Pu-240 at sites studied in convection transport increases with depth so that at a depth of 0-10 cm it is 0.21-0.38 and at a depth of 25-35 cm it is 0.60-1.56 cm yr(-1). The migration rate of Cs-137 increases with depth as well. Using the diffusion transport model the resulting migration rates of Pu-239,Pu-240 and Cs-137 range from 0.65 to 0.94 and from 0.18 to 0.99 cm yr(-1), respectively. (C) 1999 Elsevier Science Ltd. All rights reserved.