Distribution coefficients and apparent diffusion coefficients of cesium in some compacted bentonites were determined by the penetration profile method. Cylindrical compacted bentonites with the dry density of 0.8 to 1.6 Mg/m3 were contacted with tracer solutions containing 1000, 100 or 10 ppm of cesium. The apparent diffusion coefficients were obtained from the concentration profiles of cesium in compacted bentonites. The distribution coefficients were obtained concurrently by dividing the intercepts of the profiles by the concentration of the tracer solution. The apparent diffusion coefficients of cesium in compacted bentonite were obtained in the range of 0.42 to 9.6· 10−12 m2/s. The apparent diffusion coefficients in the compacted bentonite contacted with three different concentrations of cesium tended to decrease with increasing dry density of the specimen; but, they had no dependence on cesium concentration within a factor of 3 at the same dry density. The distribution coefficient of cesium for the specimens contacted with three different concentrations of cesium were obtained in the range of 0.3 to 90 L/kg and had little dependence on dry density. The distribution coefficients obtained in the compacted bentonites were dependent on pH of the solution rather than concentration of cesium. These distribution coefficients obtained in the compacted bentonites were 10 to 1000 times smaller than those obtained by batch experiments. The data suggest that not all sorption sites for cesium are available in highly compacted bentonite. It is necessary to consider surface diffusion as a significant migration mechanism of cesium through the compacted bentonites at very high pH condition such as 12.

In the safety assessment of high level radioactive waste disposal, a significant retardation of nuclides can be expected. When radionuclides released from an underground repository are transported with the moving groundwater along cracks in the rock, the radionuclides will be retarded by not only adsorption on the surface of the cracks but also diffusion into the micropores of rock matrix.

Diffusivities of U(VI) were measured in water-saturated granite that was mined in the middle of Japan. The measured penetration profile of U(VI) was composed of two parts. Those were a steep slope near the surface and a gradual slope in the deeper part. This profile was successfully explained by considering two diffusion paths in granite. One diffusion path was possibly a fissure with a width of a few microns and another was a network of submicron pores. The volume of submicron pores was approximately 80% of the total pore volume in the granite. The orders of magnitude of apparent diffusivities for U(VI) were 10−13-10−12 m2/s through the fissure and 10−15 m2/s through the network of pores. The ratio of geometrical factors in the two paths was also calculated from each apparent diffusivity and was almost unity. This ratio calculated suggests that the pore network in the granite matrix has a similar shape to the fissure, thus the microstructure of the granite seems to be fractal.

Adsorption coefficient and penetration behavior of U(VI) in Itado tuff were measured. The migration behavior of U(VI) in the tuff was discussed.

Adsorption coefficient of U(VI) was measured by a batch method using a wafer specimen and a powder specimen in pH region from 2 to 7. Adsorption coefficient was 17000 m1/g at the pH value of 5.5.

Penetration behavior of U2− (VI) in Itado tuff was studied as a function of pH, concentration of CO32− and temperature by contacting the rock specimen with U(VI) solution. The concentration profile and fractional amount of U(VI) penetrating into the rock specimen Mt/M were measured. The penetration behavior of U(VI) was seen to be diffusion accompanied by adsorption/desorption process. In the pH region from 3 to 4, it is likely that the penetration process of U(VI) is not sufficiently reversible but is competitive process consisting of diffusion and adsorption. In the pH region above 6, penetration depth was very thin because of both large adsorption coefficient and large adsorption rate constant.

The sectioning method was found to have an advantage to see the penetration behavior directly. But in the pH region from 6 to 7, the method has a shortage that diffusion coefficient, and adsorption and desorption rate constant could not be determined, because of small penetration depth of U(VI). From this point of view, the measurement of the fractional amount of penetration as a function of time should be carried out as well as that of concentration profile.

Simulated radioactive waste glass was irradiated in a nuclear reactor and radiation damage was induced by 10B(n,0)7Li reaction up to 0.14 displacement per atom. Static leach tests of the activated waste glass were carried out at 40°C, up to 38 days. Concentration of elements in leachate was determined by gamma-spectrometry. The leach test of non-irradiated glass was also performed at 40°C up to 82 days in which the solution concentration of elements was determined by an atomic absorption analysis. Leach results are given in terms of normalized elemental mass loss for the seven elements Na, K, Cs, Ca, Zn, La and Ce. Normalized elemental mass loss of alkali ions was proportional to square root of time and then, was proportional to time. Normalized elemental mass loss of alkali earth ions did not show such a simple tendency. Build up of zinc on the waste glass surface was observed following its initial leaching. It was also found that theleach rate of Cs, Zn and Ce decreased with increase of irradiation exposure of waste glass.