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.
A 1 Ci Pu−Be neutron source and a low-background beta-spectrometer were used to activate and to measure the beta-rays of low-activity.
The main characteristics of this method can be given as follow: The determined S/N ratio increases because the background
beta-rays are lower than the gamma-rays. For example, the sensitivity obtained for quantitative analysis of sulphur in silicon
is 100 ppm in case of S/N=1.0.
Aerosol-size distributions of218Po were determined for the accelerator tunnel air sampled during machine operation and for the basement air of a concrete
building, where the number and the size distribution of non-radioactive aerosols are greatly different from each other. The218Po distributions depended very much on the size distributions of ambient non-radioactive aerosols, and could be well explained
by an attachment model of218Po to ambient non-radioactive aerosols.
Authors:Y. Kanda, Y. Oki, A. Endo, M. Numajiri, and K. Kondo
The irradiation of atmospheric air with high-energy protons has been performed at the 12 GeV proton synchrotron. The specific activity of 13N, one of the principal airborne radioactivities, was measured as a function of the irradiation time at a dose rate of about 6·1016 eV/g/s, and compared with the calculated values. The predominant chemical species of 13N produced were found to be 13N2and 13NO2. Their proportions were approximately 55% for 13N2 and 45% for13NO2, being almost independent of the irradiation time. Smaller quantities of 13NO and H13NO2 were also observed. Measurements of radiolytic products showed that ozone is a main product and that NO2predominates among the products of nitrogen compounds, including HNO2 and HNO3. The G-value for ozone formation in air was estimated from the experimental data as 6.4 molecules/100 eV.
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:K. Kondo, H. Kawabata, N. Akata, J. Inaba, O. Mitamura, Y. Seike, Y. Ohmomo, and S. Ueda
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.
Authors:K. Kondo, H. Kawabata, S. Ueda, N. Akata, O. Mitamura, Y. Seike, J. Inaba, and Y. Ohmomo
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
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.
Authors:H Kataoka, J Nakano, Y Kondo, Y Honda, J Sakamoto, T Origuchi, and M Okita
This study examined the aging effect on disuse muscle atrophy prevention using heat stress. Wistar rats aged 7 and 60 weeks were divided into three groups as follows: control, immobilized (Im), and immobilized and heat stressed (ImH). Heat stress was given by immersing the hindlimbs in hot water (42 °C) for 60 min, once in every 3 days and the gastrocnemius (GAS) and soleus (SOL) muscles were extracted after 14 days. Muscle-fiber types were classified using ATPase staining. Heat shock protein 70 (HSP70) was assessed through Western blotting. In GAS muscle of both groups and SOL muscle of 7-week-old rats, the fiber diameter of each muscle type in the ImH group significantly increased compared with that in the Im group. However, this could not be observed in the SOL muscle of the 60-week-old rats. The increased percentage of type-I fibers and variability of types I and II muscle-fiber diameter were evident in the SOL muscle of the 60-week rats. HSP70 was significantly elevated in the ImH group compared with in the Im group in both muscle types of both age groups. Thus, effectiveness of heat stress in the prevention of disuse muscle atrophy appears unsatisfactory in aging muscle fibers.