Research on migration behavior of radionuclides is very important in the safety assessment of radioactive waste disposal in geosphere. In particular, the properties of humic substances such as structure, behavior of functional groups in the complex formation should be well studied. Determination of the concentrations of humic substances is very difficult.

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  The effects of pH and ionic strength of eluting solutions on the release of kaolinite particles from quartz surfaces were investigated in a packed column. Flowing of eluting solutions of low ionic strength resulted in the release of kaolinite particles regardless of pH, and there was a critical ionic strength above which no release of particles took place. We calculated the double layer potentials with surface potentials (measured or estimated) and the van der Waals potentials to obtain the total interaction potentials between quartz and kaolinite particles. It was found that the critical ionic strength observed relatively agreed with that predicted from the barrier of total interaction potentials.

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  Adsorption and migration experiments of ⁸⁵Sr in a coastal sand have been performed by a batch and a column methods respectively, in order to study influence of coexistent humic acid on adsorption and migration behavior of radionuclide in a geological medium.
  Humic compounds of ⁸⁵Sr, which were hardly adsorbed on the sand, were formed in the solution containing humic acid. However, distribution coefficient of ⁸⁵Sr for the sand, determined by the batch method, was not affected by coexistent humic acid. This was attributed to that the binding force between ⁸⁵Sr and humic acid was significantly smaller than that between ⁸⁵Sr and the sand. Migration amounts of ⁸⁵Sr into a deeper region of sand layer in the column increased under coexistence of humic acid, because a dissociation process of the humic compounds did not equilibrate in experimental condition of the column method. Such migration behavior of ⁸⁵Sr could be evaluated by applying the migration model talking account of kinetics in the dissociation process.

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  Transport behaviors of colloids through a compacted and saturated bentonite were studied experimentally by using hydraulic conductivity test method for colloidal gold. In this test, the colloidal gold particles were about 15 nm in diameter and the bentonite was compacted at dry density 1.0 g/cm³ . We found experimentally a filtration effect of the bentonite for the colloidal gold.

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  Based on the results from potentiometric titrations carried out on polyacrylic acid and some commercially available humic acids, the equation for the proton dissociation of weak polymeric acids is proposed to be K_app ＝ [H^＋]α/(1－α) ＝ K_1/2{(1－α)/α}([Na^＋]/[Na^＋]_s), where α is the degree of dissociation, K_1/2 is the dissociation constant at α ＝ 1/2, and the brackets with subscript s denote the concentration at the surface of the polymer. This equation has been derived on the assumptions: (i) Each polymer molecule is a polybasic acid (H_NR_N) having different acidic sites with K values from K₁ to K_N. (ii) Binding energies of protons on these sites are all equal. (iii) The ratios of the dissociation constants of H_N－iR_N^i－ and H_N－jR_N^j－ is expressed by K_i/K_j ＝ {(N－i＋1)/i}/{(N－j＋1)/j} since the probabilities to release or bind a proton are proportional to the numbers of protons or numbers of available anionic sites on the polymer. (iv) The effective concentration of protons at the surface of the polymer ([H^＋]_s) is related by [H^＋]_s/([H^＋] ＝ [Na^＋]_s/[Na^＋], where [Na^＋]_s can be estimated by the relation, [Na^＋]_s ＝ [Cl^－]_s＋[R^－]_s (where [R^－]_s ＝ ∑i[H_N－iR_N^i－]). This leads to [Na^＋]_s ⋍ [Cl^－]_s, which in turn leads to [Na^＋]_s ⋍ [Na^＋] at high ionic strength and [Na^＋]_s ⋍ [R^－]_s ＝ C_Rα at low ionic strength.

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  Activities and tolerance of some bacteria were investigated under alkaline and reducing conditions for geological disposal. A fermenter was used to control pH and Eh with a liquid culture inoculated with sulphate-reducing bacteria (SRB), methane-producing bacteria (MPB) and sulphur-oxidizing bacteria (SOB). Growth of SRB was obtained at maximum pH 8.6 (Eh －340 mV) or maximum Eh －100 mV (pH 7). Ranges of Eh for the growth of MPB and SOB were estimated to be less than －210 mV at pH8, and more than ＋240 mV at pH 7.5, respectively. Activity for SOB was not observed in the pH range more than 8.

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  Organic content and availability as nutrients were investigated for bacteria in compacted bentonite and asphalt material, and possibilities of bacteria migration in compacted bentonite were examined. Total organic carbon and humic substances in the bentonite (Kunigel V1) were estimated more than 0.30 to 0.35 wt%, 0.5 to 10 ppm, respectively. Bacteria in groundwater were propagated in the presence of bentonite as much as twofold greater than in the absence of it. A straight asphalt was separated into 4 fractions by solvent extraction and by chromatographic technique. Growth of some Pseudomonas strain was observed in some fractions. Finally, the experimental system was shown for a better understanding of bacterial migration in compacted bentonite.

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  This review focused on aquatic humic substances in groundwater. Humic substances are large molecular，heterogeneous mixtures of many organic compounds and comprise a major fraction of dissolved organic materials in natural waters. Humic substances may play an important role related to the migration behavior of TRU nuclides in underground layer because of the high complexation affinity to TRU nuclides. This report summarized characteristics (elemental composition，functional groups，molecular weight，etc.) of humic substances in groundwater and stability constants for TRU nuclides-groundwater humates.

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  The migration of radionuclide through the buffer material was analyzed by considering the precipitation caused by decay-chain ingrowth. In the analysis, the temporal and spacial isotopic ratio in the buffer material was taken into account for determining the shared solubility for each radionuclide. The release rate of radionuclide from the outer surface of buffer material to surrounding rock is generally lower in such realistic analysis considering precipitation in the buffer material than calculated by the model neglecting precipitation. This result shows the model not considering such effects is more conservative for the safety assessment. It is also shown that the realistic analysis considering precipitation defined by the shared solubility can provide a large margin in the safety assessment.

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  A radioactive metal ion must be removed from contaminated soil which accidentally adsorbs the radioactive metal ion. With this situation, the authors examined the diffusion dialysis as a removal process of the radioactive ion from fine particles of the soil. In a dialyzer, the one side of the solution including fine particles of soil was referred to as diluting cell and the other side stripping was referred to as concentrating cell. The experiments by batch operations were carried out by interposing a cation exchange membrane (CMV) between both cells. The high separation of the ion from the soil could be achieved by the experiments when the aqueous solution of hydrochloric acid was used as stripping solution. Equations for batch diffusion dialysis system were set up and calculated. From the results of simulation, it was noted that the concentration of hydrochloric acid in the stripping solution, the selections of the membrane, and mass transfer coefficient at the surface of the membrane strongly affect the removal efficiency of the ion.

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