[en] Plutonium (Pu) isotopes, being characterized as strong chemical and radiological toxicity, are high risky for human health, and study on Pu concentrations and distributions is an important part for environmental assessment of human nuclear activity. The information of Pu in the soils of China has been expanded benefiting from the improvement of measuring methods and the increasing scientific and public concern in recent years. The activity of ^239+240Pu in surface soils from different areas of China varies, but typically less than 1 mBq/g. It was indicated by prophase results that no influence from Chinese Nuclear Test Site (CNTS) to the upwind areas of that was observed. However, the Pu inventory of some points from downwind areas of CNTS is five times higher than that of global fallout, which was suggested to be the influence of CNTS. Further field investigations in detail are necessary to master the total figure of CNTS. For the areas far away from CNTS, Pu inventory and ²⁴⁰Pu/²³⁹Pu are both similar with global fallout. The forms of Pu vertical distribution vary for different soils, depending upon various factors (e.g. soil type, weather condition). (authors)

[en] Atmospheric deposition of Pu isotopes from the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident has been observed in the terrestrial environment around the FDNPP site; however, their deposition in the marine environment has not been studied. To fully understand this possible contamination of Pu isotopes from the FDNPP accident to the marine environment, we collected marine sediment core samples within the 30 km zone around the FDNPP site in the western North Pacific about two years after the accident. Pu (²³⁹Pu, ²⁴⁰Pu, ²⁴¹Pu) and radiocesium (¹³⁴Cs, ¹³⁷Cs) isotopes were determined. The high activities of radiocesium and the ¹³⁴Cs/¹³⁷Cs activity ratios with values around 1 (decay corrected to 15 March 2011) revealed that these samples were heavily contaminated by the Fukushima-released radionuclides. However, the activities of ^239+240Pu and ²⁴¹Pu were comparable with the background level before the FDNPP accident. The Pu atom ratios (²⁴⁰Pu/²³⁹Pu and ²⁴¹Pu/²³⁹Pu) suggested that global fallout and the Pacific Proving Ground (PPG) close-in fallout are the main sources for Pu contamination in the marine sediments. As Pu isotopes are particle-reactive and they can be easily incorporated with the marine sediments, we concluded that the release of Pu isotopes from the FDNPP accident to the marine environment was negligible. (author)

[en] The activity of ^239+240Pu in surface soils from different areas of China varies, but typically less than 1 mBq/g. It was indicated by previous study that no influence from Chinese Nuclear Test Site (CNTS) has occurred to the upwind areas. However, the Pu inventory at one point in downwind areas of CNTS is five times higher than that of global fallout and ²⁴⁰Pu/²³⁹Pu atom ratio in one lake sediment is below 0.18, which were suggested to be the influence of CNTS. Further field investigations in detail are necessary to master the total figure of CNTS. For the areas far away from CNTS, Pu inventory and ²⁴⁰Pu/²³⁹Pu atom ratio are both similar with global fallout. The forms of Pu vertical distribution vary for different soils, depending upon various factors (e.g. soil type, weather condition). (authors)

[en] In this study, a detail evaluation is made of the new sector-field ICP-MS (Element XR) on its analytical potential for ultra-trace determination of Pu isotopes. In order to enhance the sensitivity for Pu isotope analysis, high efficiency sample introduction systems (APEX-Q and Aridus II) were combined with the Element XR. A detection limit at attogram (10^-18 g) level was obtained, which is comparable or even better than that of AMS, indicating a significant advance of ICP-MS for ultra-trace Pu isotope measurements. (author)

No abstract available

[en] The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident led to the release of large amounts of radionuclides into the environment. In addition to the atmospheric releases, the direct discharges of highly contaminated water from the damaged reactor buildings resulted in contamination of radionuclides in the sea. It has been estimated that the total amount of ¹³⁷Cs released from the FDNPP accident ranged from 15-35 PBq, while for the refractory actinides, in particular, Pu isotopes, tiny amount (^239+240Pu/¹³⁷Cs activity ratio of ca. 10^-7-10^-8 in heavily contaminated environmental samples) was released into the environment. The released radioactive materials posed radiation threat to human society. Thus, source identification of radioactive contamination and long-term environmental behaviour of released radioactive materials are important issues of study after the FDNPP accident. In this work, we made accurate isotope ratio analysis for radioactive Cs isotopes (¹³⁵Cs/¹³⁷Cs atom ratio) and Pu isotopes (²⁴⁰Pu/²³⁹Pu and ²⁴¹Pu/²³⁹Pu atom ratios) in environmental samples collected in Fukushima Prefecture before and after the FDNPP accident. We identified the isotopic compositions of radioactive Cs and Pu isotopes released from the FDNPP accident, and estimated the released amounts of ¹³⁵Cs and Pu isotopes. We demonstrated that radiocesium in the terrestrial environment was mainly released from the Unit 2 reactor. The potential applications of the obtained FDNPP-sourced Cs and Pu fingerprints in the study of long-term environmental behaviour of the released radioactive materials will also be discussed. (author)

No abstract available

[en] As a widely accepted method of measuring ultra-trace level Plutonium isotopes in environment samples, the most difficulty and inaccuracy of ICP-MS measurement is from the interference of matrix elements, mainly uranium. In this research, we employed acid digestion and a two-stage anion chromatography for extraction and purification of Pu from soil and sediment samples, which can achieve high decontamination factor of uranium up to 1.5 × 10⁵. By introducing a APEX-IR sampling system combined with a Spiro membrane desolvation unit, the yields of polyatomic interferences ²³⁸U¹H⁺ and ²³⁸U¹H₂⁺, which are the main interferences of ²³⁹Pu and ²⁴⁰Pu, are as low as 3.4 × 10^-5 and 7.6 × 10^-6, respectively. In case of using this method to analyze the Pu level of Chinese soils and sediments, the relative tolerances of measured results are supposed to be less than millesimal. The detection limit of this method for ²³⁹Pu and ²⁴⁰Pu are respectively 3.6 fg/mL and 7.3 fg/mL. This method is validated by analyzing soil and sediment reference materials IAEA-soil-6 and NIST-4357, both the ^239+240Pu concentration and ²⁴⁰Pu/²³⁹Pu atom ratio correspond well with the certified values. (authors)

[en] On March 11, 2011, a catastrophic tsunami induced by a magnitude 9.0 earthquake caused the terrible Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, leading to the release of a large amount of radionuclides into the environment. The published studies on plutonium isotopes in the environment after the FDNPP accident were reviewed in this paper. The total atmospheric released amounts of Pu from the FDNPP accident were estimated to be 10⁹ Bq, that is only 1/10000 of that released from the Chernobyl accident. The Pu isotopes were released from the damaged reactors, not from the spent fuel pools in the FDNPP. The Pu isotopic ratios (²⁴⁰Pu/²³⁹Pu, ²⁴¹Pu/²³⁹Pu) and activity ratios of A(²³⁸Pu)/A(^239+240Pu) were significantly different from that of global fallout, serving as powerful fingerprints for Pu source identification. To date, the plutonium isotopes from the accident in the terrestrial environment within the 30 km zone around the FDNPP site have been widely observed and there are no strong positive correlations between the Pu isotopes contamination levels and the distances from the FDNPP site. The influence of the FDNPP accident on Pu distributions in the marine environment is limited. No detectable Pu contamination from the accident is observed even in the near coastal (5 km off the FDNPP site) marine sediments. (authors)

[en] The ultra-trace level of Pu (plutonium) isotopes in Chinese surface soil are mainly resulted from global fallout following the world-wide atmospheric nuclear tests last century. The vertical migration behaviors of Pu in soil were studied by field sampling and laboratory measurements using AMS (Accelerator Mass Spectrometry) and ICP-MS (Inductively Coupled Plasma Mass Spectrometry). Subsequently by fitting the vertical distribution of ^239+240Pu with the solution of convection-dispersion equation in single pulse condition, the apparent convection coefficient V in Chinese soils was found to be 0.046-0.163 cm/a, the apparent diffusion coefficient D ranged from 0.058 to 0.339 cm²/a and the migration velocity of ^239+240Pu concentration peak in soils of different areas from 0.063 to 0.187 cm/a. Based on these, the predicted ^239+240Pu concentration peak would remain in top 10 cm of the surface soil in Chongqing city after 200 years' migration. The results indicated that the organic matter content of soil would be a key factor influencing the migration behavior of Pu. Besides, other soil parameters such as porosity, soil particle size, cation exchange capacity etc. tend to have influences on the migration velocity of Pu in soils. (authors)