Processes affecting long-term change in Cs abundance in seabed sediment off Fukushima

Otosaka, Shigeyoshi; Kobayashi, Takuya

no journal, , 

The Cs abundance in surface sediment in the coast off Fukushima decreased at the rate of about 30%/year. In this study, we assessed the three processes, (1) vertical mixing of sediment, (2) offshore transport of Cs bound particles, and (3) desorption of Cs from sediment, that may affect the decrease in the Cs abundance. The process (1) was assessed by applying time-series data of vertical distribution of sedimentary Cs into a pulse input sediment mixing model. The model estimated up to 70% of Cs in the coastal sediment was efficiently transported to the lower sedimentary layers in the first 5 years after accident. In conclusion, we consider that the primary process decreasing the Cs abundance in surface sediment is vertical mixing of sediment due to bioturbation or storm events.

Groundwater colloid properties in sedimentary rocks; Preliminary results from the Horonobe URL

Sasamoto, Hiroshi; Ohara, Shigeru*

no journal, , 

In the present study, a non-destructive technique using Particle Tracking Analysis (PTA) has been tested to determine size distribution and concentration of colloids in groundwater. The groundwaters were sampled from water-rings (4 samples) located in the vertical shafts and boreholes (6 samples) drilled in the drifts of the Horonobe URL. Results suggest that colloid particle concentrations range from 9.110 to 7.810 particle/mL (pt/mL) and the estimated colloid mass concentrations range from 3.410 to 4.2 mg/L for the diameter of 1 to 1000 nm, respectively. Colloid concentrations of groundwater sampled from water-rings are generally higher than those sampled from boreholes due to differences in groundwater sampling conditions. For sizes 100 nm of particles, colloid stability was evaluated on the basis of DLVO theory. DLVO theory predicts that particle sizes 100 nm would be unstable (i.e., coagulation could occur). Particle and mass colloid concentrations in the groundwater were therefore reevaluated to obtain the reliable colloid particle concentrations range from 5.810 to 3.010 pt/mL and colloid mass concentrations range from 2.010 to 1.310 mg/L for the diameter range 100 nm, respectively. Furthermore, the reevaluated results indicate a negative correlation between colloid concentrations and IS of groundwater.

The Millennium scale monsoon cycles recorded in a sediment core from alpine Tibetan lake

Watanabe, Takahiro; Nara, Fumiko*; Matsunaka, Tetsuya*; Minoura, Koji*; Kakegawa, Takeshi*; Yamasaki, Shinichi*; Tsuchiya, Noriyoshi*; Nakamura, Toshio*; Junbo, W.*; Liping, Z.*

no journal, , 

Understanding of past environmental and geochemical changes is significant issues to estimate global climate variation. Therefore, these changes have been studied by continuous terrestrial sediments. The high-time resolution past environmental changes, especially monsoon fluctuations, have been reported in previous studies using geochemical signatures in stalagmites from Asian caves. However, continuous climate records in Tibetan plateau have not yet been cleared, which a key area to understand mechanism of monsoon fluctuations. In this study, mean grain size and geochemical proxies from lake sediment cores from south Tibetan plateau were used for estimation of past monsoon changes during Holocene. Spectral analysis of the mean grain size in the Tibetan lake indicated 1000-1500 years climate cycles, which might be caused by the changes in solar activities. These monsoon fluctuations based on the mean grain size were also supported by geochemical proxies in this study.

The JAEA thermodynamic database for reactions between groundwater, cement, clay, zeolite and/or rock forming minerals

Walker, C.; Arthur, R. C.*; Wakiya, Arata; Suto, Shunkichi; Sasamoto, Hiroshi; Oda, Chie; Mihara, Morihiro; Honda, Akira

no journal, , 

The JAEA thermodynamic database for reactions between groundwater, cement, clay, zeolite and/or rock forming minerals Summary: Reactions between groundwaters, cement, clay, zeolite and/or rock forming minerals will control the geochemical evolution of a repository built for the geological disposal of radioactive waste in Japan. JAEA has therefore developed a thermodynamic database (TDB) to simulate and assess the impact of these different reactions on the safety and performance of the repository. The thermodynamic properties of all relevant items have been written into formats supporting the geochemical computer programs SUPCRT92, Geochemists Workbenchtextregistered and PHREEQC.

A Survey on new standard materials for U-Pb dating of carbonate using LA-ICP-MS

Yokoyama, Tatsunori; Kokubu, Yoko; Murakami, Hiroaki; Watanabe, Takahiro; Hirata, Takafumi*; Sakata, Shuhei*; Danhara, Toru*; Iwano, Hideki*; Maruyama, Seiji*; Miyazaki, Takashi*; et al.

no journal, , 

Chronological and geochemical studies of carbonates, which are commonly found as fracture filling minerals in rocks, can provide information about geochemical conditions present during formation including in deep subsurface environments. A dating technique for the carbonates using laser ablation-multiple collector-inductively coupled plasma mass spectrometry (LA-MC-ICPMS) is still immature partly because of a lack of a consensus international carbonate standard for the in-situ dating technique. In this study, we performed a survey on the carbonate standard materials that may be suitable for high precision U-Th-Pb dating using LA-MC-ICPMS. We examined carbonate standard materials JCp-1 and JCt-1 issued by the Geological Survey of Japan (GSJ). Based on solution-based bulk analysis using MC-ICP-MS, heterogeneities in Pb isotope compositions were confirmed. Nevertheless, the 206Pb-based isotopic compositions were all within 1.2 per mill variations acceptable for a standard used for age determination using LA-MC-ICPMS. Additional tests on the heterogenities in U-Th-Pb compositions of the carbonate standards along with determinations of other trace elements using a 2D imaging LA-ICP-MS are ongoing. Examinations on both natural standards and synthetic standards are ongoing for further efforts in determination of the standard suitable for U-Th-Pb dating of carbonates.

Hydrochemical evolution process at the Horonobe area, northern part of Japan

Mizuno, Takashi

no journal, , 

How to use hydrochemical data to improve long-term groundwater flow simulations?

Amano, Kenji; Alexander, W. R.*

no journal, , 

For the purpose of improving the reliability of geological environment models, we have developed newly modelling methods that to be able to evaluate groundwater flow regime affected by natural events and processes. In addition to that, some approaches for reduction uncertainties in long-term groundwater flow simulations are proposed by the actual hydrochemical data obtained from the boreholes in the Horonobe Town, Hokkaido.

Seasonality of Cs-137 concentration of sediments eroded from a slope in Fukushima

Wakiyama, Yoshifumi*; Manome, Ryo*; Onda, Yuichi*; Yoshimura, Kazuya

no journal, , 

Pseudocolloid formation of Uranium with soluble surface glycoprotein of Paramecium

Kozai, Naofumi; Sakamoto, Fuminori; Tanaka, Kazuya; Sato, Takahiro; Kamiya, Tomihiro

no journal, , 

When living Paramecium cells were exposed to a U(VI) aqueous solution, U was hardly detected in the cells, while U was clearly detected in the Paramecium cells that were pre-killed with a fixative before exposure to the U aqueous solution. The U in the liquid phase after the experiment was found to bound to a large soluble glycoprotein to form pseudocolloid. We discuss the relation between these results and the soluble glycoprotein covering the cell surface of Paramecium.

Specific sorption processes of REEs and actinides induced by biomolecules

Tanaka, Kazuya; Tani, Yukinori*; Onuki, Toshihiko*

no journal, , 

We investigated sorption of rare earth elements (REEs) and actinides on biogenic Mn oxide. Sorption experiments of REEs showed a negative Ce anomaly under circumneutral conditions. SEC-HPLC-ICP-MS analysis confirmed that Ce was complexed with organic ligands in solution. A line of data indicates that the negative Ce anomaly under circumneutral pH conditions arose from Ce(III) oxidation on biogenic Mn oxide and subsequent complexation of Ce(IV) with biomolecules. Th(IV) was sorbed, and then desorbed from biogenic Mn oxide with time. The desorption of Th(IV) is possibly attributed to organic ligands released from fungal cells as observed in the Ce sorption. In contrast, sorption of Pu(IV) increased with time, which was similar to that of U(VI). Plutonium(IV) was possible to be oxidized to Pu(VI) by Mn oxide. Sterilized biogenic Mn oxide did not show the desorption behavior of Th(IV), indicating that living cells would release organic ligands strongly complexed with Th(IV).