Migration rates and distribution coefficients of fallout <'239+240>Pu and <'137>Cs, and natural<'210>Pb in soils of un-cultivated grassland around the nuclear fuel reprocessing plant in Rokkasho, Japan

摘要

Vertical migration rates and distribution coefficient (K<,d>) of fallout <'239+240>Pu and <'137>Cs were evaluated in soils of un-cultivated grassland around Japan's first commercial nuclear fuel reprocessing plant in Rokkasho, Japan, for understanding their behaviors and mobility in the soil. Anthropogenic <'210>Pb originating from atmospheric deposition was also examined for comparison with those nuclides. Migration rates of <'239+240>Pu, <'137>Cs and <'210> Pb were estimated to be 0.08-0.34, 0.10-0.30 and 0.09-0.31cm·y<'-1>, respectively, from the vertical distribution and deposition histories of these nuclides. The K<,d> values for Pu, <'137>Cs and <'210>Pb ranged 1.3×10<'2>-1.5×10<'3>, 9.1×10 <'1>-1.6×10<'3> and 9.1×10<'1>-1.6×10<'3>, respectively. Although the present K<,d> values of Pu and <'137>Cs for fallout radionuclides were within the range of reported values, our data were in lower side, indicating faster migration rates. The K<,d> value of <'210>Pb was approximately one order of magnitude lower than the reported value of stable Pb. The K<,d> of Pu and <'137>Cs values exponentially increased with ignition losses of the soils, showing their slower mobility in soil with higher organic matter content.