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  • Author or Editor: S. Ueda x
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Abstract  

The aim of this study was to measure the distribution and inventories of 239+240Pu, 137Cs, and excess 210Pb (210Pbexcess) in sediment core samples from brackish Lake Obuchi, which is in the vicinity of nuclear fuel facilities in Rokkasho Village, Japan. The inventory of the 239+240Pu activity in the sediment samples from the estuary of a freshwater river, the central point of the lake, and the deepest point in the lake were 0.18, 0.29, and 0.24 kBq·m–2, respectively. The inventories of 137Cs and 210Pbexcess in sediments were 0.83–1.2 kBq·m–2 and 25–30 kBq·m–2, respectively. The mean 239+240Pu/137Cs and 210Pbexcess/137Cs activity ratios were 0.23 and 28, respectively. The239+240Pu/137Cs activity ratios were approximately 13–24 times the ratio expected from global fallout. The inventories of 239+240Pu and 210Pb in sediments were higher than the inventory expected from atmospheric fallout, but the 137Cs inventory was significantly lower than expected.

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Summary  

Major and trace elements in soil and plant samples, including standard reference materials were determined by means of neutron activation analysis (NAA) and inductively coupled plasma-mass spectrometry (ICP-MS). The analytical procedure for NAA utilized dried powder samples. The concentration of iodine in soil samples was determined by radiochemical NAA. The irradiated samples were cooled and then counted with a Ge gamma-ray detector connected to a multi-channel analyzer. For ICP-MS analysis, the samples were decomposed by microwave digestion with an acid mixture. The concentration of I in the soil samples was measured by ICP-MS after separation by ignition. The analytical values for most elements in the environmental samples by both methods were in good agreement, whereas sample treatments were different. Measured value of Zr in the soil samples by ICP-MS was about 50% lower than that by NAA. It should be assumed that some minerals of Zr in soil particles were not entirely dissolved by the acid mixture. Analytical results of Cd for three different Cd levels in unpolished rice flour samples (NIES 10-a, b and c) determined by ICP-MS were in agreement with certified values. The concentration of Cd in the sample with the lowest Cd level, as determined by NAA with 57% counting error, was 3 times higher than the certified value.

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Abstract  

The behavior of uranium under various redox conditions was investigated in the brackish Obuchi lake surrounded by an uranium enrichment plant and facilities currently under construction for reprocessing of spent nuclear fuel in Rokkasho Village in northern Japan. Our investigation showed that uranium in water under oxic conditions can be explained by the simple mixing of freshwater and seawater, and the source of uranium in the lake is mainly seawater. The ratios of 238U/salinity under oxic conditions were approximately 0.09-0.12 g.l-1.psu-1. However, the ratios of 238U/salinity in bottom layer water under anoxic condition in summer were lower (0.07-0.09 g.l-1.psu-1) than those in seawater. 238U concentrations in pore water sampled under anoxic conditions were very low (0.05-0.06 g.l-1.psu-1). Moreover, the relationships between the 238U/Al ratios and the Fe/Al ratios of particle substances were strongly correlated. This suggests that uranium in the bottom-layer water may be precipitated to an insoluble form in the anoxic state, and Fe is the major carrier of insoluble uranium.

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Summary  

In order to evaluate the transport of 3H and 137Cs radionuclides in semi-closed brackish Lake Obuchi, Japan, bordered by nuclear fuel cycling facilities, a 3D-lower-trophic eco-hydrodynamic model has been developed and validated. In a short-term prediction, 3H and 137Cs activity levels in water should be in an agreement with field measurements. It became clear that the results depended on the mixing of fresh water and seawater in the model. Moreover, a short-term simulation estimated that most 3H and 137Cs flowed to the ocean rather than remaining in the lake. Based on calculations over the past 50 years, a peak of 137Cs in sediment was in 1963, when the maximum 137Cs fallout was observed. The calculation showed a rapid decrease after that peak, however, the field measurement data gradually declined. This suggested that the process by which 137Cs accumulated from the watershed to the lake was actually slower in the field than in the model calculations. The model may be successfully applied to a variety of different environmental situations as a generic tool for evaluating the concentration and migration of 3H and 137Cs in a brackish lake.

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Summary  

In order to identify the concentration of tritium (3H) in areas of fresh, brackish and sea water, bordered by nuclear fuel facilities at Rokkasho-Village, Aomori, Japan, water samples were collected from 2001 to 2004 at six points in those areas. Concentration ranges of tritium in fresh river water, brackish lake and seawater samples were 0.60 to 1.1 Bq. l-1(mean value 0.79 Bq. l-1), 0.20 to 0.87 Bq. l-1(mean value 0.41 Bq. l-1), and 0.08 to 0.25 Bq. l-1(mean value 0.15 Bq. l-1), respectively. Relationships between tritium concentrations and salinity in the samples showed a clear negative correlation. Moreover, the seasonal variation of tritium in water from Rokkasho-Village was high in spring and low in fall.

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Abstract  

Excess enthalpies of six binary mixtures of CH3 OD+CH3 OH, CH3 OD+CD3 OD, CD3 OD+CH3 OH, C2 D5 OD+C2 H5 OH, C2 D5 OD+C2 H5 OD, C2 H5 OD+C2 H5 OH have been determined over the whole range of mole fractions at 298.15 K in order to know the isotopic effect on hydrogen-bonding accurately, although there are many reports on the differences in the strength of hydrogen-bonding between OH and OD. All excess enthalpies measured are very small and endothermic. The mixtures of CH3 OD+ CH3 OH, and C2 D5 OD+C2 H5 OH showed the largest excess enthalpies among each methanol and ethanol mixtures. The difference of intermolecular interaction between OH and OD in methanol and ethanol was almost same value of (1.820.04) J mol-1 Excess enthalpies of 1,4-dimethylbenzene+1,3-dimethylbenzene and 1,4-dimethylbenzene+1,2-methylbenzene were measured by three different principle calorimeters at 298.15 K in order to know the precision of calorimetry for a small enthalpy change.

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Abstract  

The suspended particles floating in the seawater have the ability to biologically, as well as physically adsorb radionuclides and other elements dissolved in seawater. We have studied the distribution and composition of suspended particles, as well as the state of eluted of radionuclides in the decomposition process, in the coastal waters off Rokkasho Village, where radionuclides will be discharged from a nuclear fuel reprocessing plant in the near future.

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Abstract  

The phase transitions of Ba2-xSrxIn2O5 were investigated with various thermal analyses and high-temperature X-ray diffraction. It was clarified that crystal structure of Ba2-xSrxIn2O5 with x=0.0~0.4 varies from brownmillerite through distorted perovskite to another distorted perovskite with increase of temperature. The phase transition from brownmillerite to distorted perovskite was revealed to be first order, whereas transition from distorted perovskite to another one was second order. The specimen with x≥0.5 showed only one first order phase transition from brownmillerite to distorted perovskite. The phase diagram of Ba2-xSrxIn2O5 was established and existence of tricritical point at ~1100C with x=0.4~0.5 was suggested.

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Abstract  

A survey was conducted to determine the concentration levels of 3H, 137Cs, 90Sr, 238,239+240Pu, and 234,235,238U in seawater off Rokkasho Village, Japan, before the start-up of a nuclear-fuel reprocessing plant. The level, fluctuation range and distribution characteristics of each radionuclide was determined

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