Thermodynamic studies on the solubility of actinides in the presence of organic acids related to geological disposal

Kobayashi, Taishi*; Teshima, Takeshi*; Wang, P.*; Sasaki, Takayuki*; Kitamura, Akira

no journal, , 

We focused on the complexation of U(IV) and U(VI) with isosaccharinic acid (ISA) and measured U(IV) and U(VI) solubility in the presence of ISA. The solubility dependences on hydrogen ion concentration (pHc) and ISA concentration revealed the dominant U(IV) and U(VI) ISA complexes and determined their formation constants. Furthermore, the solubility of Zr(IV), as an analogous of An(IV), in the presence of organic acids with different number of hydroxyl groups were investigated to elucidate the strong complexation ability of ISA.

Comprehensive study of the migration property in representative rock of Japan at underground research laboratories

Iwatsuki, Teruki; Ishii, Eiichi

no journal, , 

The paper reviews the applicable knowledge of the migration properties in deep underground gained by R&D in Mizunami and Horonobe URL. Summing up the major migration path, it is necessary to consider the fracture continuity / connectivity of hundreds of meters in granite of Mizunami area, while several hundred meters in the shallow part of sedimentary rock and of tens m scale in the deep part of Horonobe. On the other hand, it was also demonstrated that analogue elements are practically immobile in rock masses and closed galleries.

Thermodynamic study of complexation of deep groundwater humic acid by calorimetry

Kimuro, Shingo; Terashima, Motoki; Tachi, Yukio; Kitatsuji, Yoshihiro; Miyakawa, Kazuya; Akiyama, Daisuke*; Sato, Nobuaki*; Kirishima, Akira*

no journal, , 

Humic acid is confirmed to be present even in deep underground where radioactive wastes are planned to be disposed. Although the characteristic properties and reaction mechanism of humic acid are strongly affected by its origin, the reaction enthalpy and entropy for groundwater humic acid complexation are only estimated values obtained from the equilibrium constants at different temperature despite these thermodynamic quantities is necessary for the discussion of reaction thermodynamics. In this study, the thermodynamic quantities of the complexation of deep groundwater humic acid at Horonobe, Hokkaido, Japan with copper (II) and uranyl (VI) ion were determined by the combination of the potentiometry and calorimetry to cultivate a better understanding of the reaction mechanism. By the comparison of thermodynamic quantities with typical humic acid and simple organic acid, the characteristic reaction mechanism of Horonobe humic acid was revealed. In addition, thermodynamic equilibrium calculations based on the determined thermodynamic quantities were performed for the discussion of the impact of humic acid complexation and the origin of humic acid in the migration of radionuclide.

Sensitivity analyses of natural tracer profiles in sedimentary rocks of the Horonobe URL, Japan

Sasamoto, Hiroshi; Arthur, R. C.*; Alt-Epping, P.*; Tachi, Yukio

no journal, , 

The present study performed an interpretation of natural tracers (non or weakly sorption elements) profiles of groundwater observed in the boreholes drilled from the surface around the Horonobe Underground Laboratory based on the transport processes of advection and diffusion. In the interpretation, due to several uncertainty ranges for transport parameters in initial and boundary conditions, sensitivity analyses considering the relevant model parameters defined uncertainty limits were also conducted to evaluate the plausible parameter sets and conditions to be compatible with observations.

Boron sorption in Na-montmorillonite

Chen, Y.; Sawaguchi, Takuma

no journal, , 

Sorption of boron in compacted Na-montmorillonite was studied for a better understanding of the boron migration behavior. Boron adsorption at various pH and ionic strength conditions was investigated by batch studies. Sorption distribution ratio value (K [m/kg]) was found to be at the order of magnitude of -3. At fixed pH, sorption can be described using Freundlich isotherm expressions. Boron sorption generally increased with pH. Above about pH 8, however sorption decreased. It was assumed that adsorption was via ligand exchange with aluminol groups at clay surfaces. Both charges of adsorbent and adsorbate were taken into account to explain the pH effects.

Evaluating the mass transport characteristics for fault zone in mudstone at the Horonobe Underground Research Laboratory

Takeda, Masaki; Ishii, Eiichi; Ono, Hirokazu; Tachi, Yukio; Ito, Tsuyoshi*; Nemoto, Kazuaki*

no journal, , 

Estimation of sorption reduction by organic ligands in actinide-cement systems

Ochs, M.*; Dolder, F.*; Tachi, Yukio

no journal, , 

Numerical study on sorption kinetics of radiocesium in forest soil

Kurikami, Hiroshi; Malins, A.; Niizato, Tadafumi; Iijima, Kazuki; Tsukada, Hirofumi*

no journal, , 

This study examined the evolution of reversibly sorbed Cs in forest soil using a vertical transport model considering kinetic sorption. The simulated distributions and physicochemical forms of Cs were consistent with measurements, indicating the modelling approach was reasonable. The results suggest that Cs concentrations in wild animals are somewhat linked with the concentration of reversibly sorbed Cs in forest soil.

An Experimental study of microbial effect on simulant fuel debris

Liu, J.; Dotsuta, Yuma; Kitagaki, Toru; Kozai, Naofumi; Yamaji, Keiko*; Onuki, Toshihiko

no journal, , 

Fuel debris was formed in severe accident in nuclear power plant. After the confirmation of microorganisms in water in damaged plant, it is necessary to consider the element migration of fuel debris. Here, some widespread bacteria were applied. By cultivation with simulant fuel debris, the migration mechanism was estimated.

Radiocesium in sewage sludge ash

Kozai, Naofumi; Suzuki, Shinichi; Sakamoto, Fuminori; Onuki, Toshihiko

no journal, , 

A fraction of radiocesium (Cs) released by the Fukushima Daiichi Nuclear Power Plant accident was accumulated in sewage sludge ash (SSA). It was previously reported that more than 80% of Cs is fixed in iron oxides of SSA and approximately 10% of Cs is tightly fixed in unidentified amorphous silicon oxides of SSA. This study reports that silicon in paper flowing in sewage and that in organic flocculant added to sewage at sewage treatment plants are origin of the silicon in SSA. Next, to contribute to developing measures for SSA disposal, we prepared geopolymer and cement solidified bodies containing SSA and evaluated their characteristics. We report a high barrier performance of geopolymer solidified bodies.