Authors:S. Ueda, H. Hasegawa, Y. Takaku, and K. Kondo
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.
Authors:M. Hirabayashi, M. Matsuo, S. Hasegawa, S. Kobayashi, and K. Tanabe
Airborne particulate matter was collected at the intersection of Industrial Road in Kawasaki-city, Kanagawa, Japan using a
12-stage low-pressure impactor. High concentrations of airborne particulate matter have been observed in this area. The collected
samples were analyzed for 34 elements by instrumental neutron activation analysis (INAA), and data on the elemental concentrations
were obtained. High concentrations of fine particles of As, Br, Sb, V, and Zn were observed. It was further observed that
these fine particles were originated predominantly from the wear of tires and brakes, and not from automobile exhaust emissions.
In this paper, several small-scale screening test methods were discussed on evaluating the thermal hazard of reactive substances.
Generally the sensitivities of DSC and ARC are not high enough to evaluate the thermal hazards for all reactive substance,
especially, for those of complex reactions containing a phase and/or chemical reaction mechanism change in the lower temperature
range. Using the C80, however, the reaction can easily be detected in the lower temperature range due to its high sensitivity.
Therefore, the C80 gives generally more accurate results than DSC and ARC. Data from C80 and Dewar vessel were compared and
it indicates that the Dewar vessel has also high enough sensitivity to evaluate the thermal hazard and determine the heat
flux in lower temperature range of reactive substances.
Authors:T. Kambara, K. Hasegawa, H. Yoshioka, Y. Kamiya, T. Kotani, and K. Tabei
Variations of125Sb valency states in HCl solutions were investigated by the use of the N-benzoyl-N-phenyl-hydroxylamine (BPHA) extraction
method.125Sb(V) is completely reduced to Sb(III) by one hour refluxing in conc. HCl.125Sb(III) is gradually oxidized to Sb(V) in solutions of low HCl concentrations by the effects of their own radiations. Natural
light promotes such oxidation reactions. By utilizing such oxidation-reduction effects125Sb(V) can be easily prepared from125Sb(III) and also125Sb(III) can be prepared by the reduction of Cl
. Their valency states were stable on keeping them in brown-colored bottles at 6M HCl concentrations.
Authors:C. Shimasaki, T. Kanaki, S. Takeuchi, K. Hasegawa, D. Horita, E. Tsukurimichi, and T. Yoshimura
The pyrolysis of trimethylsilyl derivatives of saccharides (1) was investigated by DTA-TG, MS, GC/MS and TG-GC/MS. The DTA-TG/DTG
curves showed that the pyrolysis of 1 occurred in one stage. The exothermic peaks were due to sublimation or thermal decomposition
by vaporization. The cleavage mechanism by electron impact of 1 was classified into four categories: 1) stepwise elimination
of the side-chain, 2) cleavage of the side-chain, 3) cleavage of the pyranose ring, and 4) cleavage of the pyranose ring and
side-chain at the same time. The mass-spectrum for 1 revealed the main common four fragment ions, such asm/z 73, 191, 204 and 217, with cleavage of the pyranose ring. These fragment ions were detected with a similar retention time
in the gas cromatogram by GC/MS or TG-GC/MS. The retention time for 1 increased in the sequence aldopentose<ketohexose<aldohexose.
This result indicates that the trimethylsilyl derivatives are thermally stable. Subsequently, the pyrolysis regime for 1 obeyed
apparent 1/2-order kinetics and their apparent activation energy was estimated as 75–100 kJ/mole.
Authors:Naofumi Akata, H. Kawabata, H. Hasegawa, T. Sato, Y. Chikuchi, K. Kondo, S. Hisamatsu, and J. Inaba
The atmospheric concentrations and deposition fluxes of 7Be and 210Pb were observed biweekly in Rokkasho, Japan on the Pacific Ocean coast at the northern end of Honshu Island, from March 2000
to March 2006, to clarify their regional features. Seasonal variation pattern of atmospheric 7Be concentrations had double peaks, and that of 210Pb had a single peak. Deposition fluxes of 7Be and 210Pb showed the same patterns. The total deposition pattern of 7Be was similar to that commonly seen on the Pacific Ocean side of northern Honshu Island, while the pattern of 210Pb was similar to that commonly seen on the Japan Sea side. The lack of high spine mountains windward in Rokkasho may be the
cause of this ambiguity in the winter monsoon season. Total deposition velocities and scavenging ratios of 210Pb were similar to those of 7Be from spring to fall, and showed that both nuclides had a similar removal process from the atmosphere. However, the scavenging
ratios of 210Pb were slightly larger than those of 7Be in winter, indicating different behaviors for both nuclides in the scavenging process. The scavenging ratios of both nuclides
inversely correlated with precipitation rate, and the ratios in winter were larger than in the other seasons.
Authors:H. Hasegawa, N. Akata, H. Kawabata, Y. Chikuchi, T. Sato, K. Kondo, and J. Inaba
7Be deposition fluxes and atmospheric concentrations were measured at Rokkasho Village, Aomori Prefecture, Japan, from 2000
to 2005. It was confirmed that the 7Be deposition fluxes were minimum in summer, and the fallout maximizes in winter. The atmospheric concentration of 7Be was especially low in summer, and high in the other three seasons. A positive correlation was observed between the amount
of precipitation and 7Be deposition. Clear seasonal differences were evident among the ratios of 7Be deposition flux to precipitation amounts in the four seasons. The ratios were especially high in winter, higher than those
in the other three seasons. 7Be deposition flux was estimated by a simple simulation model using atmospheric 7Be concentrations and local meteorological data. As a result, the estimated deposition value was relatively lower than the
measured value in winter.
Authors:N. Akata, H. Kawabata, H. Hasegawa, K. Kondo, T. Sato, Y. Chikuchi, S. Hisamatsu, and J. Inaba
Atmospheric concentrations of 210Pb change with various factors such as meso-scale meteorological conditions. We have already reported the biweekly atmospheric
210Pb concentrations in Rokkasho, Japan for 5 years and found that they had clear seasonal variations: low concentrations in
summer and high values in winter to spring. To study the reasons for the seasonal variations, the origins of the air mass
flowing to Rokkasho were analyzed by 3-D backward air mass trajectory analysis. Routes of the calculated trajectories were
classified into four regions: northeastern and southeastern Asian Continent, sea and other regions. The atmospheric 210Pb concentrations were well correlated with the frequency of the routes through the northeastern Asian Continent. A non-linear
multiple regression analysis of the 210Pb concentrations and the relative frequencies of the four routes showed good fitting of the predicted values to the observed
ones, and indicated that the atmospheric 210Pb concentrations in Rokkasho depended on the frequency of the air mass from the northeastern Asian Continent.
Authors:K. Kondo, H. Kawabata, S. Ueda, H. Hasegawa, J. Inaba, O. Mitamura, Y. Seike, and Y. Ohmomo
We investigated the distribution of aquatic plants and the absorption of radionuclides by them in the brackish Lake Obuchi, Japan, which is bordered by nuclear fuel cycle facilities. We studied 5 species of submerged plants: Zannichellia palustris, Ruppia maritima, Potamogeton pectinatus, Zostera japonica, and Z. marina. The plants contained many elements, including radionuclides. The concentrations of 238U, 137Cs, and 90Sr in Z. marina were 11.3-12.4, 0.000-0.144, and 0.151-0.202 Bq.kg-1 dw, respectively. Those in Z. japonica were 5.2-8.8, 0.000-0.267, and 0.081-0.175 Bq.kg-1 dw, respectively. The concentrations of these radionuclides in the plants tended to be higher in higher-salinity regions than in lower-salinity regions of the lake. We found a close relationship between photosynthetic activity and the absorption of stable Sr by plants in the laboratory. Salinity, illumination, and water temperature influenced the photosynthetic activity of the plants and the consequent absorption of elements.