137Cs behavior in the system soil – plant in the stationary sampling sites located within the 30-kilometer zone of the Chernobyl NPP in the period 1987-1992: II. Vertical migration in soils and accumulation of 137Cs in natural meadow grasses

Abstract

It was shown that on the territory of 30-km area around the Chernobyl nuclear power plant highlighted 2 zones, which differ in the form of depositions of radionuclides. The first, which was called the "near" zone, dominated by the fuel component; the second, named "remote" zone, dominated by the condensation component. In the "near" to the reactor zone properties of 137 Cs were largely determined by the occurrence of the radionuclide within transformed fuel particles and composite reactor's materials (primarily, graphite) besides o SAC (soil adsorbtion complex). The radiocesium incorpoprated in composition of graphite particles, during the entire period of study (1986)(1987)(1988)(1989)(1990)(1991)(1992) have been gradually leaching out of them, while remaining readily available for plant uptake. At the same time, most of 137 Cs located in SAC, due to irreversible fixation by clay minerals of the soil became inaccessible for plants. As a result, during the period of research the mobility of radiocaesium in the system "soil-plant" was higher in "near" to the reactor zone, than in "remote" with a predominance of condensation forms of the radioactive fallout: the transfer factors (TF) of 137 Cs in "near" zone, in average, turned out in 1988 to 1.6 in 1989 to 2.4 in 1990 to 3.1, and in 1992 to 4.0 times higher than in "remote" zone.In lysimetric waters collected at sites with a predominance of the fuel components of the radioactive fallout, there was marked increased 137 Cs volume activity. Nevertheless, in the soil of the area located in the "near" zone, the content of the exchange form of the radionuclide was 2.5-7 times less in comparison with other plots, located in the "remote" zone. This may be due to the