Fig. 4-10 Concentration of radionuclides in the forest soil near the Sahan River in the Chernobyl region (sampled in September 1995) Soil sample collected were separated into surface organic and lower mineral layers and an analysis was conducted on the radionuclides. The concentration of radionuclides in the organic layer is higher than in the mineral layer. This indicates that radionuclide fixation in the organic layer may play an important role in determining the migration of radionuclides.

Fig. 4-11 Relative mobility of radionuclides in the river sediment in the Chernobyl region Relative mobility of Sr-90 is the highest among the various radionuclides released into the environment, with Pu isotopes showing the least mobility. The migration tendencies of most radionuclides showed the behavior expected from previous studies, except americium-241 (Am-241) which exhibited high mobility. The high mobility of Am-241 compared with that of other heavy metal radionuclides such as Pu and Cs-137 may be significant for estimating the radiological impact on humans from the Chernobyl nuclear power plant accident.

Detailed information on the behavior of radionuclides in the environment is required for accurate assessment of the risks associated with radioactive releases that may occur during the operation of a nuclear power plant. To better understand migration behavior and the environmental pathways leading to human exposure, JAERI is continuing to study these issues and is working toward establishing a method of assessing the radiological impact on humans. The site around Chernobyl presents some unique contamination fields of cesium(Cs), strontium(Sr) and other radionuclides. Cs and Sr are the same nuclides that occur as fallout from nuclear weapon tests. The deposits around Chernobyl also include fuel materials such as uranium(U) and other transuranic elements such as plutonium(Pu) and curium(Cm). Therefore, the Chernobyl site is valuable for experimental study of the radiological consequences mentioned above. At present, research is being conducted around the site, including river and forest areas within the exclusion zone which is 30 km around the Chernobyl nuclear power plant. Through this study, the migration behavior of radionuclides from soil to river water are being elucidated by means of radiochemical analysis which detects the presence of dissolved radionuclides in the environment and determines their physical and chemical forms.

Reference T. Matsunaga et al., Migration Behavior of the Released Radionuclides in the River System in the Exclusion Zone of the Chernobyl Nuclear Power Plant, IAEA-CN-63/143, One Decade After Chernobyl : Summing up the Consequences of the Accident (1996).

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