Modelling Radiocaesium Bioavailability in Forest Soils

Abstract

The experience of radiation accidents, the Chernobyl accident in the first place, has shown that the methodology used to develop and estimate the effectiveness of countermeasures to reduce negative consequences of accidental contamination of the environment by radionuclides does not meet the requirements of fast response in case of an emergency. In order to overcome this shortcoming, Geographic Information Systems (GIS) and computer systems for decision-making support in case of emergency are being actively developed [l]. An essential part of such systems are mathematical models of migration and transformation of radionuclides in the environment and their impact on man and components of terrestrial and aquatic ecosystems. The accuracy of prediction by these models in determining the effectiveness of decisions making is largely dependent on the accuracy of estimating input parameters [2]. In this context, it is important to create an expert system for estimation of input model parameters which would form a separate module in the decision-making system. Special emphasis should be put on those parameters to which the predictions are more sensitive. An important component in calculation of radiation dose is the estimation of the soil-plant transfer of radionuclides. For this purpose, the concentration ratio CR is normally used which is defined as the ratio of radionuclide concentrations in the plant and in the upper soil layer. The values of CR determined experimentally in different conditions for a particular plant can differ by a factor hundred or even thousand [3]. Accordingly, using a plant-average CR leads to a considerable uncertainty in prediction. For this reason, numerous attempts were made to develop methods for estimating site-specific values of CR. A great effort went into deriving empirical relations between the accumulation of radionuclides in plants and soil properties [4]. An essential drawback of purely empirical characteristics is that they are not generally valid. In order to be applied to soils different from those that they were obtained, characteristics should be justified based on information about mechanisms of sorption-desorption of radionuclides in soil and their soil-plant transfer.