Above- and belowground distribution of radiocesium released from TEPCO' FDNPP accident in the mountainous forest of Fukushima

Niizato, Tadafumi; Sasaki, Yoshito; Ito, Satomi; Mitachi, Katsuaki*; Watanabe, Takayoshi

no journal, , 

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.

Fixation of radium by adsorption on clay minerals based on analyses of core samples around Ningyo-toge uranium mine

Yamaguchi, Akiko; Kuribara, Yuichi; Okumura, Masahiko; Takahashi, Yoshio*

no journal, , 

no abstracts in English

Upward migration of radiocesium in soil via abiotic process

Sakamoto, Fuminori; Kozai, Naofumi; Guido-Garcia, F.; Kimura, Tatsuki; Grambow, B.

no journal, , 

Soil microorganisms are known to remove a fraction of tightly fixed radiocesium and make it bioavailable. In this study, we attempted to nondestructively recover available radiocesium from soil using microorganisms instead of plants. Microbial activity was tested to form bioavailable radiocesium by the comparing the addition of nutrients and microbicide. Powdered minerals, a water absorbent material, and paper towels were packed in a fine mesh cloth bag (mineral bag) with a size of 50 cm 50 cm. The radiocesium concentration analysis revealed that the surface soil contained approximately 0.3-1.2 Bq/g. The mineral mat was replaced with a new one every two weeks. Two control experiments were established: one with 1 L of nutrient solution to activate microorganisms, and another with sodium hypochlorite aqueous solution to suppress microbial activity. These solutions were added every week. After eight weeks, radiocesium concentrations of the top soil and in the soil core were measured. The accumulative radiocesium concentration in the four mats after eight weeks was within 4.210 and 9.010 Bq, indicating that the mats indeed absorbed radiocesium from soil. The driving force of upward migration of radiocesium is thought to be soil water flow due to continuous water absorption from soil by the mat and evaporation from itself. These results suggest that cesium upward migration flow along with water is a behavior expected to happen in the environment.

Cs uptake by lentinula edodes (shiitake) mushrooms

Guido-Garcia, F.; Sakamoto, Fuminori; Kozai, Naofumi; Grambow, B.; Devid, K.*

no journal, , 

The uptake of Cs by fungi has been thought to be similar to the uptake of K due to their chemical similarities. In this research we aimed to evaluate the impact of different concentrations of K in Cs uptake during mushrooms growth, as well as determine the spatial distribution of both within fruit bodies. Lentinula edodes (shiitake) was used as a model organism due to their capacity to produce fruit body. Preliminary results have shown that the concentrations of Cs in the obtained mushroom samples from mushroom bed did not show any clear relationship to the different concentrations of added K. Higher concentrations of Cs were observed in pileus than in stem, consistently. The results of Cs and K mapping did not show a significant spatial variation. This result suggest that Cs and K are distributed evenly, and that there is no specific or selective binding site for cesium.

Importance of halogen for soil decontamination using cesium-free mineralization; A Role of chlorine on phase transformation of weathered biotite

Shimoyama, Iwao; Baba, Yuji*

no journal, , 

Management of radioactive contaminated soil is an unsolved problem after the nuclear incident in Fukushima, but soil decontamination is generally difficult due to the existence of micaseous clay minerals in which radiocesium is strongly fixed. Cesium-free mineralization (CFM) can remove Cs from the soil through the conversion process from clay minerals to other minerals and the choice of reactant is critically important for this method. Because CaCl has higher decontamination efficiency than CaCO and Ca(OH) and facilitates phase transformation of clay minerals around 700C, it is deduced that Cl has a catalytic effect on phase transformation, however, the detail is not clear. In this work, Cs-sorbed weathered biotite (WB) was used as a model soil and chemical bonding states of Cl was studied using X-ray absorption spectroscopy and molecular orbital calculations. We clarified that Cl interacted with WB at 400C and Cl and higher valent Cl sites were formed by bonding with O in WB besides Cl sites in the early stage of the reaction. Because formation of Cl-O bonds can destabilize the silica network, Cl can facililate decomposition and phase transformation of WB at moderate temperatures.

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.

Computational molecular study of predominant organic molecules in forest ecosystems concerning cesium accumulation and transport

Suno, Hiroya; Machida, Masahiko; Dohi, Terumi; Omura, Yoshihito*; Sasaki, Yoshito

no journal, , 

Complexation of biomolecules with radiocesium is known to play an important role in the accumulation and migration of radioactivity on the organic matter in forests. In this work, we identify typical molecules forming a metal complex in the forest organic matter and carry out atomistic analyses by performing quantum mechanical calculations in order to understand the alkali metal cation complexation selectivity of these organic molecules. Among these molecules, of particular interest are norbadione A (CHO), a primary pigment molecule present in mushrooms, oxalic acid (CHO), atranorin (CHO), lecanoric acid (CHO), and usnic acid (CHO), main secondary metabolites in lichens.