Fig. 9-4 Main phenomena related to migration of environmental radionuclides in the surface environment

Fig. 9-5 Hypothetical environment constructed on a PC using MOGRA for Windows

Fig. 9-6 One example of cultivated land

Fig. 9-7 Example of result

An example of a model of cultivated land for time-dependent analysis of contamination of surface soil and plants, which was created using the MOGRA Compartment Model Editor, is shown (Fig. 9-6). In this figure, the soil surface and plant surfaces are first contaminated with radioactive 90Sr. We assume, for example, that the growth period of the vegetables is 60 days and that 90Sr is discharged into the environment in the initial 10 days of growth. We also assume that the 90Sr deposition on the target land is 100 Bq/m2. We then predict the 90Sr concentrations on the vegetable surfaces and inside throughout their 60-day growth period. Fig. 9-7 shows the result using the MOGRA for Windows. In Fig. 9-7, the total surface concentration of 90Sr of the vegetables reaches a maximum value immediately after the end of environmental discharge (10th day), while the concentration of 90Sr inside the vegetables reaches a maximum value 2 days after the completion of the discharge (12th day) under continuous 10-day discharge. The figure also shows that the total concentration at the harvest period after 50 days after the termination of discharge decreases to ca. 2% of the value immediately after the termination of discharge, and that most of 90Sr is inside the vegetables at the time.

To evaluate the effects of environmental-burden substances such as radioactive contaminants, it is essential to identify the migration patterns and behaviors of these substances in the environments that comprise the earth's ecosystem. The mechanisms affecting substance migration patterns and behaviors are very complicated and cover a wide range of disciplines (Fig. 9-4). In addition, as the ecosystem contains a mixed variety of land usage modes (including forests, farm fields and rice paddies), the migration patterns of the substances in each of the various land usage classifications are quite diverse. As a means of analyzing and predicting the migration of the substances under the above conditions, we have developed the fundamentals of the Migration Of GRound Additions (MOGRA) code. MOGRA consists of computational codes that are applicable to various evaluation target systems and can be used on personal computers. This code has a dynamic compartment model analysis block at its core, a graphical user interface (GUI) for computation parameter settings and results displays, data files, and so on. The compartments are obtained by classifying various natural environments into groups that exhibit similar properties. The system features near-universal applicability and excellent expandability for computations of various nuclides. An evaluation begins with a classification of the target land biosphere according to a land usage classification called a module (Fig. 9-5). Next, desired compartments are set within each module (Fig. 9-6) together with the selection of migration patterns of substances between modules. The flow of environmental-burden substances between compartments is expressed in the formulae obtained from theoretical considerations and/or scientific experimental results. When a compartment in a module is subject to pollution by an environmental-burden substance (for example when water in a rice paddy is polluted), these codes can be used to evaluate how and to what extent the surrounding environments will be polluted in the future (Fig. 9-7).

Reference H. Amano et. al., Development of a Code MOGRA for Predicting the Migration of Ground Additions and Its Application to Various Land Utilization Areas, J. Nucl. Sci. Tecnol., 40, 975 (2003). (https://www.tandfonline.com/doi/pdf/10.1080/18811248.2003.9715441)

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