Long-Term Study on the Transfer of super(137)Cs and super(90)Sr from Chernobyl-Contaminated Soils to Grain Crops

The level of super(137)Cs and super(90)Sr transfer to four grain crops and the change in transfer with time have been studied on two soils contaminated with fragments of nuclear fuel released during the Chernobyl accident. Field experiments were carried out in 1987-1994 inside the heavily contaminated zone around Chernobyl Nuclear Power Plant. Shortly after the deposition, the rate of super(90)Sr accumulation by crops was comparable with, or even slower, than that of super(137)Cs, which is in disagreement with the usual findings. In the following years, super(137)Cs uptake by plants was reduced by a factor in excess of than 50, whereas the soil-to-plant concentration ratio of super(90)Sr increased within one order of magnitude, and has remained on approximately the same level since 1991. Changes of the super(90)Sr and super(137)Cs concentration ratios for grain crops with time have been used to evaluate the rate of radionuclide leaching from fuel particles and the ageing processes.