Shinichi Takebe

Migration Behavior of Radionuclides (60Co, 85Sr and 137Cs) in Aerated Sandy Soil Layer

Differences of the migration behavior and desorption process for radionuclides (60Co, 85Sr and 137Cs) in aerated sandy soil layer were studied by sprinkle of distilled water into the contaminated soil with above nuclides in column. Influence of difference desorption process on radionuclide migration was examined by changing the volume of distilled water sprinkled like rain on the contaminated soil. Quantity of sprinkled water affected the concentration distribution of each radionuclide in soil layer. Each nuclide migrated deeper in the layer according to the increase of water amount, and especially, migration behavior of 85Sr was remarkably influenced by water amount. It is observed that as to 85Sr maximum contamination part in soil layer moved to deeper layer with increase of water amount, and that, as to 60Co and 137Cs, it moved almost never. On the other hand, activity concentration of 60Co or 137Cs in effluent was rather high (10−6 μCi/ml) compared with that of 85Sr, which could not be detected therein.

Effect of Flow Field on Colloid Deposition in Filtration Process of Polystyrene Latex Particles through Columns Packed with Glass Beads

The effect of flow field on the deposition rate of colloidal particles onto solid surface in a column packed with spherical collectors was investigated theoretically and experimentally. A new analysis for calculating the colloid deposition efficiency was developed. The analysis includes the effect of the flow field on the deposition of a colloidal particle through the interactive potential barrier between the particle and the solid surface. The deposition behavior of polystyrene latex particles (diameter: 102 nm) in transport process through columns (length: 100 mm) packed with glass beads (diameter: 0.35–0.40 mm) was observed. The colloid deposition efficiencies calculated by the new analysis were comparable with those obtained by the experiments. The result indicates that the effect of the flow field would cause the difference between the flow velocity dependence of the efficiency obtained by a classical analysis and that by the experimental results. The colloid deposition efficiencies were also obtained by estimating the deposited particles onto the glass beads surface suspended in the colloidal suspension from the SEM observation of the glass beads surface. The effect of the heterogeneity of the collector surface was discussed by calculating the colloid deposition efficiency using the evaluated interaction potential between the particle and the heterogeneous collector surface.

Development of migration prediction system(MIGSTEM) for cationic species of radionuclides through soil layers.

The migration prediction system (MIGSTEM) has been developed for estimating the migration of cationic species of radionuclides through soil layers systematically. The MIGSTEM consists of the migration experiments, the one-dimensional fitting code (inverse analysis code) for determining retardation factor and dispersivity (migration factors) and the three-dimensional differential code (prediction code) for estimating the migration of the radionuclides. The migration experiments are carried out for obtaining the concentration profiles of the radionuclides in unsaturated and saturated soil layers. Using the inverse analysis code, the migration factors are obtained at one time by fitting the concentration profiles calculated to those observed. The prediction code can give the contours of concentration and the one-dimensional concentration profiles at selected time, as well as the changing in the concentration at a selected position with time. The validity of the MIGSTEM was obtained by the benchmark test on t...

Sorption Characteristics of Actinium and Protactinium onto Soils

Sorption behavior of227Ac and 233Pa onto several kinds of soil has been studied by a batch sorption experiment and a sequential extraction technique. The sorbedform of 227Ac was mainly fractionated into a lattice-bound form in the soils, which suggests strong binding with a crystalline phase in the soils. On the other hand, most of 233Pa was fractionated into an association with amorphous Fe+Mn oxides in the soils. In addition, a linear relationship between the Kd values of 233Pa and the content of iron oxides in the soils was found. From these results, it was concluded that 227Ac and 233Pa are irreversibly sorbed to the crystalline phase and amorphous Fe+Mn oxide in the soils, respectively. Carbonate concentration dependence of the Kd values of 227Ac and 233Pa on soil was also studied to evaluate the influence of groundwater composition on the sorption behavior. The Kd values of 237Ac and 233Pa increased with increasing carbonate concentration because of the formation of carbonate complexes of 237Ac and 233Pa to be irreversibly sorbed on the soil surface.

Analysis of radionuclide migration behavior in loess medium

A five-year cooperative research program has been carried out by China Institute for Radiation Protection and Japan Atomic Energy Research Institute to develop safety assessment methodology for disposal of low level radioactive waste. Migration behavior of radionuclides {sup 3}H and {sup 85}Sr through field tests, simulation tests in the laboratory and determination of distribution coefficients is discussed and analyzed in this paper. The results show that the retardation coefficients, R{sub d}, from field tests are about 0.08--3.3 times those from simulation tests and R{sub d} from batch tests are 1.1--44 times those from field tests for {sup 85}Sr and loess medium. It was observed from field tests that radionuclides moved mainly downward under artificial sprinkling and a part of them moved up besides downward under natural rain condition. In addition, it was discovered that the retardation coefficient, R{sub d}, increases with velocity of unsaturated water flow, u, in the analysis.