Vol. 62 No. 6
A radioactivity survey program was launched in 1983 to determine the background levels of artificial radionuclides, such as 90Sr and 137Cs in the marine environment off commercial nuclear power stations. In this paper, we report on the long-term temporal changes of 90Sr and 137Cs in seawater, bottom sediment and marine organism samples. Both 90Sr and 137Cs have been detected since the beginning of the program in the seawater samples. Their concentrations decreased slowly over time, except for a prompt rise of the 137Cs concentration caused by the Chernobyl nuclear accident in 1986, and reached the level corresponding to 1-2 mBq L−1 for both radionuclides just before the Fukushima accident. The concentration of 137Cs in the bottom sediments widely varied, unlike that in seawater from one sampling site to another. The highest 137Cs concentration was observed in marine organisms in 1986, when the Chernobyl nuclear accident occurred, and was followed by relatively high concentrations for some years. The 137Cs concentration gradually decreased thereafter during the 1990s. The most recent results before the Fukushima accident suggested that the 137Cs concentration would not be more than 1-2 mBq L−1, ND (below the detection limit) to 8 Bq kg−1-dry and ND to 0.24 Bq kg−1-wet, respectively, for seawater, bottom sediment and marine organism samples. A post-accident monitoring after the Fukushima accident revealed a heavy burden of artificial radionuclides in the marine environment adjacent to Fukushima Prefecture. This paper also summarizes the 90Sr and 137Cs monitoring data in the seawaters, bottom sediments and marine organisms immediately after the accident. A comparison of data was made between the precedent situation before the accident and the post-accident situation in order to assess the impacts of the Fukushima accident on the adjacent marine environment.
We estimated the extent of radioactive contamination from each reactor unit (1 to 3) of Fukushima Daiichi Nuclear Power Station by using the 134Cs/137Cs activity ratio as an index. Although the activity ratio of 134Cs/137Cs emitted by the accident has been reported to be about 1 : 1, variations in the activity ratio has arisen in environmental samples, since the ratio differs slightly for every nuclear reactor. Therefore, it is considered that the ratio is useful for a index for evaluating the contamination from each reactor unit. We collected soils and plant pieces in eastern Japan, measured gamma rays and calculated the 134Cs/137Cs activity ratio. We also calculated the 134Cs/137Cs activity ratio in contaminated water accumulated in each reactor building (R/B) and turbine building (T/B), and compared it with the ratio of environmental samples. The data of the 134Cs and 137Cs activity concentration are presented by Tokyo Electric Power Company. As a result, it turned out that the ratio of a sample in Oshika Peninsula was about 0.91, which was lower than that of other samples, and similar to the ratio of reactor unit 1 of Fukushima Daiichi Nuclear Power Station. It is suggested that Oshika Peninsula is contaminated mainly from reactor unit 1. We also evaluated the extent of activity contamination from each reactor unit at other points.
Radiation leaks from the Fukushima Daiichi nuclear power station has occurred after the Japan’s Tohoku earthquake on March 11, 2011. Since then, by using validated analytical procedures, the behavior of radioactive materials, especially radiocesium (134Cs, 137Cs), should be investigated for not only government-initiated areawide waste management, but also for routine waste management and recycling. To confirm the necessity to improve the accuracy and precision of the current analytical procedures of radicesium in radiation-contaminated wastes, such as soil and incineration ash samples, we have conducted research for intra- and inter-laboratory comparisons on radiocesium with six participants. During an inter-laboratory study, radiocesium in activity concentration-prepared samples was measured by a Ge semiconductor detector, a NaI(TI) scintillation detector and a LaBr3(Ce) scintillation detector. The mean activity concentrations (n＝14) in roadside soil, plantation soil, agriculture soil, fly ash, bottom ash, and molten slag were 63900, 5610, 356, 21200, 3640, and 670 Bq kg−1 (the sum of 134Cs and 137Cs), respectively. The standard for Special Measures concerning the Handling of Pollution by Radioactive Materials Act in Japan is 8000 Bq kg−1 (the sum of 134Cs and 137Cs) within the obtained activity concentration range. The results demonstrated that the relative standard deviations (RSDs) for intra- and inter-laboratory data from tested samples were less than 10%, indicating participants in this research could obtain reproducible results based on intra- and inter-laboratory comparisons. In this study, small variations in the data were observed as follows: 1) variation in the intra-laboratory data for agriculture soil; the lowest activity concentration of radiocesium tended to be comparably higher than other samples. 2) A detector-dependent variation in the inter-laboratory data was also indicated.
We have developed a rapid monitoring technology for measuring the level of radiocesium (Cs) dissolved in water. This developed technology uses a cartridge filled with a nonwoven fabric, impregnated with Prussian blue (PB). Dissolved Cs was absorbed and concentrated onto PB when water passed through the cartridge. Experiments were conducted by using water samples with 0.005-5 Bq L−1 of Cs. Results showed that the recovery rate was from 83% to 98% when passed through the first and second cartridge at a flow speed of 2.5 L min−1. The recovery rate of 137Cs at the first cartridge was over 89% at flow speeds of 0.4 L min−1. Compared with the conventional pretreatment method, taking over 6 hours for the concentration of a 20 L water sample, this new technology should make available the performance of water concentration more rapidly: about 10 min for 20 L water concentration and about 50 min for 100 L water concentration. Also, it is certain that an increase in the flow volume of a water sample would decrease the analysis time of a germanium semiconductor detector.
An analytical method for short-lived nuclides in rainwater using γ-ray spectrometry combined with solid-phase extraction on an ion-exchange extraction disk has been developed. Rapid pretreatment is important in determining radioactive nuclides in rainwater, because short-lived nuclides disintegrate and decrease for sampling and measurements. The appropriate measurement time for each radioactive nuclide in rainwater was considered. The disk-shaped ion-exchange resin and chelating resin enable a simple concentration of trace metals in environmental water. A rainwater sample was passed through EmporeTM ion-exchange disks of Cation-SR and Anion-SR, pretreated with methanol for 10 minutes. The radioactivity of short-lived nuclides in rainwater samples was determined by using a HP-Ge spectrometer. Several environmental radionuclides (7Be, 131I, 134Cs, 137Cs, 212Pb, 214Pb, 212Bi and 214Bi) were identified on the gamma-ray spectra of rainwater samples. A spike test for three analytes (Tl, Pb and Bi) showed good recoveries (94 – 100%) for rainwater. The present method is more rapid than the conventional method.
After the accident at the Fukushima Daiichi Nuclear Power station on 2011 March 11, the levels of radioactive cesium isotopes in environment media have been widely monitored. For determining the levels of radioactive cesium (134Cs and 137Cs) in water samples, they are generally put in a 2 L Marinelli beaker and analyzed by a germanium semiconductor detector (abbreviated as “direct method” below). However, when the concentration of suspended solids in water is high, there is a possibility that any sedimentation of the suspended solids may change the geometry of the water in the 2 L Marinelli beaker during the measurement time; therefore, an exact analysis value may not be provided. In this research, we developed an analytical method for determining radioactive cesium in water containing suspended solids using gellant in order to overcome any geometry problem. We first evaluated the effect of any sedimentation of suspended solids on measurements of radioactive cesium isotopes in water by a “direct method”. After that, we examined the applicability of the “gelling method” developed in this study, and a traditional “filtration method” widely used as an analytical method to compare with the results obtained by the direct method. Firstly, in the direct method, when the concentrations of suspended solid in water was over 100 mg L−1, the results of the measured concentrations of each radioactive cesium were more than 120% of the calculated concentration. From this result, it was confirmed that the measured concentrations of radioactive cesium isotopes in this method tend to be overestimated. In the gelling method, the errors of the measured concentrations of radioactive cesium isotopes in highly suspended solids (100 – 10000 mg L−1) were less than 15%. On the other hand, in the filtration method, the concentration of suspended solids was applicable about 100 mg L−1; however, the result will be applicable only to the concentrations of radioactive cesium isotopes (particulate form). This result indicated that the gelling method is very suitable for measuring the concentrations of radioactive cesium isotopes in suspended water.
The nuclear accident of Fukushima Daiichi Nuclear Power Station scattered radioactive cesium, following the Tohoku earthquake on March 11, 2011. In the present work, alternative radioactivity data obtained from NaI(Tl) scintillation analyzers and a Ge semi-conductor detector were compared and evaluated with respect to the correlation of those values, the accuracies and the sensitivities using as an actual agricultural product, brown rice which was contaminated by Fukushima Daiichi Nuclear Power Station accident.
Soil can migrate to the sea through river systems by weathering; radionuclides sorbed on the soil could migrate together to the sea. In the terrestrial environment, soil is in contact with freshwater; however, after it reaches the sea, large amounts of high-salinity seawater can contact with the soil. Consequently, some radionuclides as well as stable elements would be released from the soil. To estimate the potential extractability of radionuclides from soil, the solid/liquid distribution coefficient, Kd, was used in this study. Since there were no reported Kd values for sediments in Japanese estuarine areas, the published global fallout 60Co, 90Sr, 137Cs and 144Ce activity concentration data in estuarine areas in Japan were collated first. Data suitable for obtaining Kd for sediment-seawater values were identified. The geometric means of the Kd values for 60Co, 90Sr, 137Cs and 144Ce were 1200, 23, 200 and 2000, respectively. Using the Kd differences between the terrestrial and estuarine environments, the extractability of these radionuclides from soil to seawater was estimated. Stable element concentration data for Japanese soil and estuarine sediments were also used for comparisons. It was found that the extraction of Co and Ce from soil would be negligible; however, Sr and Cs would be partially removed from the soil to the seawater. For Cs, a preliminary study on 137Cs extractability from soil in seawater was carried out. The data supported a possible Cs extraction from Cs contaminated soil in estuarine systems, which might affect the biota living in the systems.
The removal and adsorption of radioactive cesium, 137Cs or 134Cs, from contaminated soil was investigated using various extractants: sodium hydroxide, hydrochloric acid, and sulfuric acid. In this experiment, a sand sample was used as contaminated soil. Although the radioactive cesium could not be removed from the soil by using sodium hydroxide, 64% of the removal efficiency was provided at room temperature when 10 M hydrochloric acid was used. Eighty percent of the radioactive cesium was removed by using 1 M sulfuric acid containing 0.1 M thiourea at 90℃. A more than 90% removal efficiency was obtained by increasing of the volume of sulfuric acid containing thiourea. The same result was obtained using custom-made radioactive cesium removal equipment. The adsorption of the radioactive cesium was also investigated. In an experiment of concerning adsorption, contaminated water containing radioactive cesium was prepared from a contaminated sand sample. More than 96% adsorption was obtained using zeolite (clinoptilolite). However, when commercial activated carbon was used, most the radioactive cesium was hardly removed. The influence of shaking time on the adsorption of radioactive cesium was investigated by a batch-system using zeolite. As a result, a shaking time of at least 5 min showed that the radioactive cesium was quantitatively adsorbed to zeolite. The adsorptive behavior of the radioactive cesium by a flow-system was also examined using zeolite.
Cation exchange resins (calcium polystyrene sulfonate, Ca-resin and sodium polystyrene sulfonate, Na-resin) have been used as agents to improve hyperkerlemia. For removing 137Cs from the human body, the adsorption ability of the resin for 137Cs was examined and evaluated. Resin (0.03 g) and 137Cs (ca.1 kBq) were introduced into 3 mL of water, the Japanese Pharmacopoeia 1st fluid for a dissolution test (pH 1.2) and 2nd fluid (pH 6.8), respectively, and shaken. After 1-3 hours, the 137Cs adsorption (%) of Na-resin was 99% in water, 60% in a pH 1.2 fluid and, 66% in a pH 6.8 fluid. By adding potassium, the 137Cs adsorption (%) of Ca-resin was reduced. However, the 137Cs adsorption (%) of Na-resin was almost unchanged. These results show that both resins have adsorption ability for 137Cs in the stomach and the intestines. Therefore, the proposed method will be an effective means in the case of a radiological emergency due to 137Cs.
Deposition of radioactive cesium isotopes, known as 137Cs and 134Cs, from the Fukushima Daiichi Nuclear Power Station (FDNPS) causes great concern due to their long half lives. Decontamination of radioactive cesium in the environment is not easy. Deposited radioactive cesium moves slowly in the soil, and remains in the surface region unless physically disturbed. However, a selective extraction of cesium from soil particles is impossible, because cesium has been strongly absorbed on clay minerals. This study demonstrated a method for the effective decontamination of radioactive cesium by using rice chaff and straw as an adsorbent at drains for rainwater in Moriya city, Japan. After 58 days of soaking, rice chaff and straw have captured radioactive cesium from 2990 Bq kg−1 (chaff) to 13610 Bq kg−1 (straw). Moreover, it was revealed that microorgasisms on the surface of rice chaff strongly captured radioactive cesium from soil particles in water. Therefore, rice chaff and straw are effective, low-cost and safe adsorbents for the decontamination of radioactive cesium.
X-ray absorption spectra of 3d transition elements at K-edge, lanthanoides and the other period 6 elements at L-edges for 105 compounds were recorded by a laboratory-type X-ray absorption spectrometer to elucidate the chemical shift comprehensively for empirical oxidation state analysis. Apparent absorption edge energies were determined at a half of the normalized XANES, and each the chemical shifts were estimated by a slope of the edge energy plotted as a function of the oxidation number. Evaluated apparent chemical shifts, linearity of the valence dependency, and the deviations were discussed based on chemical element groups, each element being within the group, and absorption edges. The apparent chemical shifts for K-edge of 3d transition elements lay within 2±0.5 eV/valences except for Cu. The chemical shifts for L-edges of lanthanoid compounds were about 2-4 times larger than those for K-edges of 3d transition elements, and shifts for Pt, Pb and Bi of the same period elements at L-edges were at most 1.3 eV/valences. Chemical shifts for lanthanoid elements at L1-edge were 1.5 times larger than those for corresponding L3-edges.
The small-angle X-ray scattering (SAXS) covers the major disciplines of biology, chemistry and physics delivering structural and dynamic information in nanoscience, mesoscopic architectures, supramolecular structures, and nucleation/growth of crystals. SAXS is also proving to be important in archaeological, environmental, and conservation sciences, and has further indicated its ability to span wide-ranging scientific disciplines. Thus, strong needs for SAXS studies are increasing significantly in a broad range of scientific fields year by year. Based on such a background, the demand for high throughput SAXS experiments is increasing. At the synchrotron facility, Diamond Light Source, one SAXS beamline, Non-crystalline diffraction I22 is now operational and highly automated throughput small-angle X-ray scattering (HATSAXS) beamline B21 is now under construction. I22 is the Undulator beamline and wide varieties of experiments, including time-resolved experiments are attempted. Based on the concept of HATSAXS, the key feature of B21 will focuses on the automation of end-station equipment. A automated sample changer has been purchased for solution SAXS measurements on biomolecules. A robotic-arm-type automated sample changer that is capable of handling several kinds of samples in material science is also being constructed. B21 is expected to successfully provide all users highly automated throughput measurements with the highest possible reliability and accuracy. Construction of this beamline will end in the second half of 2012, and will be open for users in the early summer of 2013 after commissioning.