Isotopic evidence of plutonium release into the environment from the Fukushima DNPP accident

Characterization of typical transuranic nuclides in a reference fallout material using SF-ICP-MS

For the quality control in determining transuranic nuclides in fallout samples, this work first reported the 237Np activity concentration in a reference fallout material and further calculated the activity ratios of 237Np/239+240Pu and 237Np/241Am, and the atom ratio of 237Np/239Pu in it. The reference fallout material prepared by the Meteorological Research Institute was collected at 14 stations throughout Japan in 1963-1979. The 237Np and Pu isotopes (239Pu and 240Pu) were separated and purified using AG MP-1M anion-exchange resin, quantified using 242Pu as an isotope dilution tracer, and determined by the SF-ICP-MS. The analytical method was validated by the analysis of 4 sediment reference materials. The activity concentrations of 237Np, 239Pu and 240Pu were (25.9 ± 0.6) × 10-3, 4.10 ± 0.01 and 2.89 ± 0.04 Bq/kg, respectively, in the investigated reference fallout material. The activity ratio of 237Np/239+240Pu (3.7 ± 0.1) × 10-3 was consistent with the global fallout evaluation value. The 237Np/239Pu atom ratio of 0.561 ± 0.014 was higher than the average global fallout value of 0.41 ± 0.010, indicating the necessity of establishing regional characteristic global fallout value of 237Np/239Pu atom ratio for assessment of radioactive contamination. Comparison of the 237Np/239+240Pu activity ratios between in the reference fallout material and in soils over several decades indicated that 237Np has stronger migration capability than Pu isotopes in soils because 237Np was depleted compared to reference fallout material.

Fukushima Daiichi Nuclear Power Plant Accident: Understanding Formation Mechanism of Radioactive Particles through Sr and Pu Quantities

The Fukushima Daiichi Nuclear Power Plant accident released considerable radionuclides into the environment. Radioactive particles, composed mainly of SiO2, emerged as distinctive features, revealing insights into the accident's dynamics. While studies extensively focused on high-volatile radionuclides like Cs, investigations into low-volatile nuclides such as 90Sr and Pu remain limited. Understanding their abundance in radioactive particles is crucial for deciphering the accident's details, including reactor temperatures and injection processes. Here, we aimed to determine 90Sr and Pu amounts in radioactive particles and provide essential data for understanding the formation processes and conditions within the reactor during the accident. We employed radiochemical analysis on nine radioactive particles and determined the amounts of 90Sr and Pu in these particles. 90Sr and Pu quantification in radioactive particles showed that the 90Sr/137Cs radioactivity ratio (corrected to March 11, 2011) aligned with core temperature expectations. However, the 239+240Pu/137Cs activity ratio indicated nonvolatile Pu introduction, possibly through fuel fragments. Analyzing 90Sr and Pu enhances our understanding of the Fukushima Daiichi accident. Deviations in 239+240Pu/137Cs activity ratios underscore nonvolatile processes, emphasizing the accident's complexity. Future research should expand this data set for a more comprehensive understanding of the accident's nuances.

Pace of heavy metal pollution in the anthropogenically altered and industrialized Nakdong River Estuary, South Korea: Implications for the Anthropocene

Estuaries, vital coastal ecosystems, face growing threats from industrialization. To understand the pace of sedimentary changes and heavy metal pollution at the anthropogenically altered and industrialized Nakdong River Estuary in South Korea, we used sediment coring to reconstruct environmental change. Estuarine dam construction in 1934 shifted the sedimentary system from sand to mud, coinciding with a post-1930s mercury increase due to coal burning. Mercury concentrations in other South Korean regions surged in the 1970s, indicating proximity to emission sources matters. However, most heavy metal levels (Cu, Cd, Zn, Ag) sharply rose in the 1960s and 1970s with regional industrialization. Modern heavy metal concentrations doubled pre-industrial levels, underscoring human activities as the primary driver of Nakdong Estuary environmental changes. This emphasizes the need for a balanced approach to development and environmental preservation.

Review of the sources and behaviors of plutonium isotopes in the atmosphere and ocean

Plutonium, as well as fission products such as 137Cs, had been released into the earth environment in 1945 after the first atmospheric nuclear explosion of plutonium bomb in the desert of New Mexico (USA, July 16) and later over Nagasaki (August 9), followed then by many other explosions. Thus, plutonium cycling in the atmosphere and ocean has become a major public concern as a result of the radiological and chemical toxicity of plutonium. However, plutonium isotopes and 137Cs are important transient tracers of biogeochemical and physical processes in the environment, respectively. In this review, we show that both physical and chemical approaches are needed to comprehensively understand the behaviors of plutonium in the atmosphere and ocean. In the atmosphere, plutonium and 137Cs attach with aerosols; thus, plutonium moves according to physical and chemical processes in connection with aerosols; however, since plutonium is a chemically reactive element, its behavior in an aqueous environment is more complicated, because biogeochemical regulatory factors, in addition to geophysical regulatory factors, must be considered. Meanwhile, 137Cs is chemically inert in aqueous environments. Therefore, the biogeochemical characteristics of plutonium can be elucidated through a comparison with those of 137Cs, which show conservative properties and moves according to physical processes. Finally, we suggest that monitoring of both plutonium and 137Cs can help elucidate geophysical and biogeochemical changes from climate changes.

Ultrastructural Analysis of Large Japanese Field Mouse (Apodemus speciosus) Testes Exposed to Low-Dose-Rate (LDR) Radiation after the Fukushima Nuclear Power Plant Accident

Since the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, great attention has been paid to the impact of chronic low-dose-rate (LDR) radiation exposure on biological systems. The reproductive system is sensitive to radiation, with implications connected to infertility. We investigated the testis ultrastructure of the wild large Japanese field mouse (Apodemus speciosus) from three areas contaminated after the FDNPP accident, with different levels of LDR radiation (0.29 µSv/h, 5.11 µSv/h, and 11.80 µSv/h). Results showed good preservation of the seminiferous tubules, comparable to the unexposed animals (controls), except for some ultrastructural modifications. Increases in the numerical density of lipid droplet clusters in spermatogenic cells were found at high levels of LDR radiation, indicating an antioxidant activity rising due to radiation recovery. In all groups, wide intercellular spaces were found between spermatogenic cells, and cytoplasmic vacuolization increased at intermediate and high levels and vacuolated mitochondria at the high-level. However, these findings were also related to the physiological dynamics of spermatogenesis. In conclusion, the testes of A. speciosus exposed to LDR radiation associated with the FDNPP accident showed a normal spermatogenesis, with some ultrastructural changes. These outcomes may add information on the reproductive potential of mammals chronically exposed to LDR radiation.

Level, distribution and sources of Np, Pu and Am isotopes in Peter the Great Bay of Japan sea

Transuranium elements such as Np, Pu and Am, are considered to be the most important radioactive elements in view of their biological toxicity and environmental impact. Concentrations of 237Np, Pu isotopes and 241Am in two sediment cores collected from Peter the Great Bay of Japan Sea were determined using radiochemical separation combined with inductively coupled plasma mass spectrometry (ICP-MS) measurement. The 239,240Pu and 241Am concentrations in all sediment samples range from 0.01 Bq/kg to 2.02 Bq/kg and from 0.01 Bq/kg to 1.11 Bq/kg, respectively, which are comparable to reported values in the investigated area. The average atomic ratios of 240Pu/239Pu (0.20 ± 0.02 and 0.21 ± 0.01) and 241Am/239+240Pu activity ratios (3.32 ± 2.76 and 0.45 ± 0.17) in the two sediment cores indicated that the sources of Pu and Am in this area are global fallout and the Pacific Proving Grounds through the movement of prevailing ocean currents, and no measurable release of Np, Pu and Am from the local K-431 nuclear submarine incident was observed. The extremely low 237Np/239Pu atomic ratios ((2.0-2.5) × 10-4) in this area are mainly attributed to the discrepancy of their different chemical behaviors in the ocean due to the relatively higher solubility of 237Np compared to particle active plutonium isotopes. It was estimated using two end members model that 23% ± 6% of transuranium radionuclides originated from the Pacific Proving Grounds tests, and the rest (ca. 77%) from global fallout.

Assessment of the depositional characteristics of the Yellow River estuary from 1960s by 239+240Pu and 137Cs

The spatial and vertical distribution of 239+240Pu and 137Cs in the sediments of the Yellow River Delta was studied to evaluate the deposition dynamics in the Yellow River estuary from 1960s. The activity of 239+240Pu and 137Cs in sediment core ranged from 0.001 to 0.212 Bq/kg and 0.52-2.53 Bq/kg, respectively. A maximum accumulation peak and two secondary accumulation peaks appeared in the sediment core YR2. The average deposition rate of 8.3 cm/y for the Yellow River estuary from 1964 to 1976 was obtained. The proportion of Pu from the Yellow River net input and direct deposition to the total inventory of Pu in the estuary was assessed, with a total inventory of Pu in the abandoned estuary of 7.4 × 1010 Bq and a net input of 2.2 × 1010 Bq from the Yellow River. Pu deposited in the estuary only accounts for 18 % of the total Pu transported by the Yellow River, and most of the Pu is injected into the Bohai Sea with the Yellow River.

Spatial distribution, source identification, and transportation paths of plutonium in the Beibu Gulf, South China Sea

To investigate the spatial distribution and source of plutonium isotopes in the Beibu Gulf, surface sediments were collected and analyzed using sector field inductively coupled plasma mass spectrometry (SF-ICP-MS). The activities of 239+240Pu in surface sediments ranged from 0.012 to 0.451 mBq/g (mean: 0.171 ± 0.138 mBq/g, n = 36), indicating a decreasing trend in a counterclockwise direction from the southern bay mouth. The counterclockwise decreasing trend in the south of the bay mouth is similar to the current in the Beibu Gulf. The 240Pu/239Pu atom ratios in surface sediments ranged from 0.156 to 0.283 (mean: 0.236 ± 0.031, n = 36), slightly higher than that of the global fallout value of 0.18. This suggests that the Pu in the Beibu Gulf was a combination of global fallout and Pacific Proving Ground (PPG). The average contribution of the plutonium (Pu) derived from the PPG in the sediment was estimated to be 52 % ± 24 %.

Assessment of soil-soil solution distribution coefficients of global fallout 237Np and 239Pu in Japanese upland soils

Neptunium-237 and ²³⁹Pu are important radionuclides in the safety assessment related to geological disposal of radioactive waste because of the possibility of long-term exposure to humans. Mobilities of these radionuclides in the environment are of particular importance for their radiation dose evaluation; therefore, in this study, we have made the assessment of the soil-soil solution distribution coefficient (K_d, L/kg) using global fallout ²³⁷Np and ²³⁹Pu in Japanese upland soils. The K_d values were determined by extracting these radionuclides from 24 soil samples using a laboratory batch method. The desorption K_d values of ²³⁷Np ranged from 3.3 × 10² to 1.0 × 10⁴ L/kg, and their geometric mean (GM) and arithmetic mean (AM) were 1.7 × 10³ L/kg and 2.6 × 10³ L/kg, respectively. The desorption K_d values of ²³⁹Pu were found to vary from 9.4 × 10³ to 7.1 × 10⁴ L/kg, and their GM and AM were 3.3 × 10⁴ L/kg and 4.0 × 10⁴ L/kg, respectively. In Japanese upland soils, the K_d value of ²³⁹Pu was one order of magnitude higher than that of ²³⁷Np.

Plutonium in sediments of the Eastern Guangdong coast-its sources and their contribution

The ^239+240Pu activities and ²⁴⁰Pu/²³⁹Pu atom ratios of surface sediments from the Eastern Guangdong coast (EGDC) were determined by sector field ICP-MS in order to examine the sources of plutonium (Pu) and quantify their contributions. The ^239+240Pu activities in the EGDC ranged from 0.113 to 0.451 Bq kg^-1, with an average of 0.225 ± 0.090 Bq kg^-1 (n = 17). Consistently high ²⁴⁰Pu/²³⁹Pu atom ratios, ranging from 0.218 to 0.274 (average = 0.254 ± 0.014, n = 17), indicate a non-global fallout Pu source in the EGDC. The horizontal distribution of the ²⁴⁰Pu/²³⁹Pu atom ratios in the EGDC sediment suggests the non-global fallout Pu is sourced from close-in fallout from the Pacific Proving Grounds (PPG). Using a simple two end-member mixing model, we calculated the relative proportions of Pu from the PPG and global fallout in the EGDC to be 57 ± 9 % and 43 ± 9 %, respectively. Moreover, from the well-defined relationship between ^239+240Pu activity and total organic carbon content in sediments and a two end-member mixing model using δ¹³C, we further calculated the Terr-global fallout (riverine input) and Mar-global fallout (direct atmospheric deposition) to be 11 ± 2 % and 32 ± 6 %, respectively. Finally, from the activity levels and atom ratios of Pu isotopes in the EGDC, we established a baseline for future use in environmental risk assessment related to nuclear power plant operations.

Vertical distribution of plutonium isotopes from the floodplain and lacustrine sediments in Poyang Lake, China

Anthropogenic radionuclides deposited in sediments have been used for environmental radiation risk valuation as well as source identification. In this study, we investigated the vertical distribution of plutonium (Pu) isotopes and ²⁴⁰Pu/²³⁹Pu atom ratios in both floodplain and lacustrine sediments in Poyang Lake. The ^239+240Pu activity concentrations in floodplain sediment cores were found to range from 0.002 to 0.085 Bq kg^-1, with a maximum value at the subsurface layer. The activity in lacustrine sediment cores was from 0.062 to 0.351 Bq kg^-1 with a mean of 0.138 ± 0.053 Bq kg^-1. The inventory of 43.15 Bq m^-2 in lacustrine sediment core is comparable to the average value of global fallout expected at the same latitude. The average ²⁴⁰Pu/²³⁹Pu atomic ratios (0.183 ± 0.032) for sediment cores indicated that the global fallout is the major source of Pu in the studied region. The results are of great significance to the further understanding of sources, records, and environmental impacts of regional nuclear activities in the environment.

Potential Airborne Releases and Deposition of Radionuclides from the Santa Susana Field Laboratory during the Woolsey Fire

ABSTRACT

The Santa Susana Field Laboratory (SSFL), located in southern California, is a former research facility, and past activities have resulted in residual radioactive contamination in Area IV of the Site. The Woolsey Fire burned across the site, including some of the contaminated areas, on 8-11 November 2018. Atmospheric transport modeling was performed to determine where the smoke plume went while the fire burned across the SSFL and the deposition footprint of particulates in downwind communities. Any radionuclides on vegetation and in surface soil released by the fire were assumed to follow particulate matter transport path and deposition. The predicted deposition footprint was used to guide confirmatory soil sampling at 16 locations including background. Highest offsite deposition was determined to be northeast of the Oak Park community, which is located about 6 km southwest of SSFL. Depth-profile sampling was used to evaluate whether radionuclides of SSFL origin were potentially emitted and deposited during the Woolsey Fire. If radionuclides had been deposited from the Woolsey Fire at sufficient concentrations, then they would be detected in the surface layer and would be expected to be higher within the plume footprint than outside it. An upper bound estimate of the hypothetical effective dose to a person in Oak Park based on measured radionuclide concentrations in soil and vegetation on the SSFL was less than 0.0002 mSv. The occurrence of naturally occurring radionuclides at concentrations above the established background for the SSFL was attributed to natural variability in geologic formations and not SSFL. No anthropogenic radionuclides were measured at levels above those expected from global fallout. The soil sampling confirmed that no detectable levels of SSFL-derived radionuclides migrated from SSFL at the locations sampled because of the Woolsey Fire or from past operations of the SSFL.

Simultaneous Determination of Transuranium Radionuclides for Nuclear Forensics by Compact Accelerator Mass Spectrometry

Accelerator mass spectrometry (AMS) is one of the most sensitive techniques used to measure the long-lived actinides. This is particularly of interest for determination of ultra-trace transuranium nuclides and their isotopic fingerprints for nuclear forensics. In this work, a new method was developed for simultaneous determination of transuranium nuclides (Np, Pu, Am, and Cm isotopes) by using 300 kV AMS after a sequential chemical separation of each group of actinides. ²⁴²Pu and ²⁴³Am were utilized as tracers for Np/Pu and Am/Cm yield monitoring. The results show that the chemical behaviors of Np and Pu on the TK200 column and those of Am and Cm on the DGA column were very consistent in 8-9 mol/L of HNO₃ and 0.015-0.03 mol/L of NaNO₂ media during the radiochemical separation. The AMS detection efficiencies for transuranium nuclides were also evaluated. The detection limits for all radionuclides are below femtogram level and even in attogram level for Pu and Cm isotopes. The established method has been successfully applied to accurately measure various transuranium nuclides in a single actinide radionuclide solution, demonstrating its feasibility for nuclear forensic investigation.

Temporal evolution of plutonium concentrations and isotopic ratios in the Ukedo - Takase Rivers draining the Difficult-To-Return zone in Fukushima, Japan (2013-2020)

In 2011, the Fukushima Dai-Ichi Nuclear Power Plant (FDNPP) accident released significant quantities of radionuclides into the environment. Japanese authorities decided to progressively reopen the Difficult-To-Return Zone after the decontamination of priority reconstruction zones. These areas include parts of the initially highly contaminated municipalities located to the north of the FDNPP, including Namie Town, an area drained by the Ukedo and Takase Rivers. Eleven years after the accident, research focused on the spatial distribution of plutonium (Pu) and radiocesium (Cs) isotopes at contrasted individual locations. To complement previous results, the current research was conducted on flood sediment deposits collected at the same locations after major flooding events during eleven fieldwork campaigns organised between 2013 and 2020 at the outlet of the Ukedo and Takase Rivers (n = 22). The results highlighted a global decrease of the Pu and ¹³⁷Cs contents in sediment with time during the abandonment phase in the region, from 2013 (238.20 fg g^-1) to 2020 (4.28 fg g^-1). Furthermore, based on the analysis of the ²⁴⁰Pu/²³⁹Pu isotopic ratios, the plutonium transiting these rivers (range: 0.166 - 0.220) essentially originated from the global fallout (0.180 ± 0.014 (Kelley et al., 1999)). Sediment showed contrasted properties in the two investigated rivers, which is likely mainly the result of the occurrence of Ogaki Dam on upper sections of the Ukedo River as it strongly impacts the material supply from this river to the Pacific Ocean. A statistical analysis highlighted the strong correlation between Pu activity concentrations and ¹³⁷Cs activities in both rivers, confirming that both radionuclides are transported with a similar pathway. Despite it was detected early after the accident (2011-2013), the current research demonstrates that plutonium originating from FDNPP is no longer detected in these rivers draining the Difficult-To-Return Zone at the onset of the reopening of the area to its former inhabitants.

Plutonium Signatures in a Dated Sediment Core as a Tool to Reveal Nuclear Sources in the Baltic Sea

Plutonium distribution was studied in an undisturbed sediment core sampled from the Tvären bay in the vicinity of the Studsvik nuclear facility in Sweden. The complete analysis, including minor isotopes, of the Pu isotope composition (238Pu, 239Pu, 240Pu, 241Pu, 242Pu, and 244Pu) allowed us to establish the Pu origin in this area of the Baltic Sea and to reconstruct the Studsvik aquatic release history. The results show highly enriched 239Pu, probably originating from the Swedish nuclear program in the 1960s and 1970s and the handling of high burn-up nuclear fuel in the later years. In addition, the 244Pu/239Pu atomic ratio for the global fallout period between 1958 and 1965 is suggested to be (7.94 ± 0.31)·10-5. In the bottom layer of the sediment, dated 1953-1957, we detected a higher average 244Pu/239Pu ratio of (1.51 ± 0.11)·10-4, indicating the possible impact of the first US thermonuclear tests (1952-1958).

An overview of plutonium isotopes in soils, China: Distribution, spatial patterns, and sources

Plutonium (Pu) is an anthropogenic radionuclide which has drawn significant attentions due to its radiotoxicity, and the sources of plutonium linked with nuclear accidents and contaminations. The ²⁴⁰Pu/²³⁹Pu atom ratio is source dependent and can be used as a fingerprint to determine the sources of radioactive contaminant. However, the distribution and sources of plutonium in soils of China have not yet been systematically studied at a national scale up to date. The distribution, spatial patterns, and sources of plutonium in soils of China were discussed in this work. The concentrations of ^239,240Pu are in the range of 0.002-4.824 mBq/g with a large variation, and the ^239,240Pu concentrations in surface soils increase with the increasing latitude, which affects by multi-factors such as organic matter and particle size, etc. The inventories of ^239,240Pu are in the range of 7.31-554 Bq/m². The weighted average of ²⁴⁰Pu/²³⁹Pu atom ratios (0.180 ± 0.004) in all surface samples is good agreement with the ratio of global fallout (0.180 ± 0.014) of the nuclear weapons tests, this indicate that the major source of plutonium in China is global fallout. However, among some sites, distinctly lower ²⁴⁰Pu/²³⁹Pu atom ratio compared to the global fallout values were observed in the northwest China, indicating a significant contribution from other source besides the global fallout. Furthermore, the spatial clustering patterns of hot spots (high values) and cold spots (low values) for plutonium showing the clear associations with nuclear tests, especially the Chinese Lop Nor nuclear weapons tests (CNTs) and the Semipalatinsk nuclear weapons tests (STS). Radioactive material including plutonium from the STS or CNTs was transported by the prevailing westerlies to the northwest China. This review about the fingerprints and distribution of plutonium in soils of China will help researchers to establish a reference database for future radiation risk assessment and environmental radioactive management.

Distributions of fallout 137Cs, 239+240Pu and 241Am in a soil core from South Central China

The source and vertical distribution of ¹³⁷Cs,^239+240Pu and ²⁴¹Am activity concentrations in a soil core from Hunan Province, China were investigated. The maximum ¹³⁷Cs and ^239+240Pu activity concentrations were 15.45 ± 0.76 mBq/g and 0.819 ± 0.066 mBq/g, respectively. While the maximum ²⁴¹Am activity concentration in samples obtained from the core was 0.341 ± 0.019 mBq/g. The ²⁴⁰Pu/²³⁹Pu atom ratio and the ¹³⁷Cs/^239+240Pu activity ratio were 0.183 ± 0.011 and 19.5 ± 1.8, respectively, and both were consistent with the characteristic value of global fallout. The integrated ²⁴¹Am/^239+240Pu activity ratio for global fallout was also re-estimated. The measured ²⁴¹Am/^239+240Pu activity ratio (average 0.43 ± 0.07) in the samples was very close to the estimated value (0.45), which suggested their ²⁴¹Am also came from the global fallout. Regarding the vertical distribution of ¹³⁷Cs, ^239+240Pu and ²⁴¹Am in these red soil samples, all these radionuclides had higher concentrations in upper layers of several centimeters of soil while they had slightly lower concentrations in lower soil layers down to 30 cm. Vertical distributions of ¹³⁷Cs/^239+240Pu and ²⁴¹Am/^239+240Pu activity ratios indicated the migration velocity was Am ≈ Pu > Cs. The intrinsic chemical properties of the radionuclides as well as soil type and properties (acidic, nutrient-deficient and low in organic matter and cation exchange capacity) might be reasons for the differences in their migration behaviors.

Plutonium isotopes in the Qinghai-Tibet Plateau: Sources, distribution, and their environmental behaviors

Due to the high radiotoxicity in high concentrations, plutonium isotopes have drawn high attentions in the consideration of radiation risk, their sources, level, environmental behaviors, including deposition, retention and migration behaviors. However, such research in the Qinghai-Tibet Plateau is still missing, where is deemed as an environmental sensitive area. ^239,240Pu in surface soil collected from the Qinghai-Tibet Plateau were determined for the first time in this work. The concentrations of ^239,240Pu are in the range of 0.0176-1.95 Bq/kg, falling into the reported ranges in the background areas from the similar latitude belt. The ²⁴⁰Pu/²³⁹Pu atomic ratio range was measured to be 0.146-0.225, which is similar with the global fallout values. Both indicate that the global fallout is the major source of plutonium in this region, and the low plutonium level will not cause any radiation risk so far. Based on the statistical analysis of the possible parameters (organic content, moisture content, average annual precipitation, altitudes, topography and human activity), the large variations of ^239,240Pu concentrations were mainly attributed to the retention process related factors including soil organic content and human activity disturbances. While, the deposition related factors including the average annual precipitation, altitudes, topography made insignificant influence on the spatial distribution of ^239,240Pu concentrations due to the low ^239,240Pu concentrations in atmosphere, less wet deposition amount and insignificant re-suspended amount. The highest ^239,240Pu concentrations of 0.805-1.95 Bq/kg were mainly due to the good retention condition in the sampling sites with higher soil organic content and less human activity disturbances.

Prompt digestion and HPIC separation of rare earth elements in surrogate post-detonation debris material with detection by ICP-MS and gamma spectroscopy

Prompt analysis of fission products and rare earth elements (REE)s in post-detonation nuclear debris is critical for nuclear forensic analysis. In this work the compatibility of ammonium biflouoride fusion and microwave digestion in combination with high pressure ion chromatography (HPIC) separation was examined for the analysis of REEs. The refractory geological materials USGS G-2, QLO-1a, AGV-2 and BHVO-2 were used as surrogate post-detonation debris. The HPIC separation used a mixed bed ion exchange column with a gradient elution consisting of oxalic acid and diglycolic acid mobile phases. Quantitative recovery for seven REEs was achieved using the in-line HPIC-ICP-MS. An off-line HPIC method was also developed to separate U, Pu, and REE fission products. Collected fractions were analyzed by ICP-MS or gamma ray spectroscopy. The offline HPIC separation with detection of short-lived fission products with gamma ray spectroscopy had detection limits 5-20,000 times lower than quadrupole ICP-MS for stable REEs.

Distributions and impacts of plutonium in the environment originating from the Fukushima Daiichi Nuclear Power Plant accident: An overview of a decade of studies

This paper reviews the current knowledge on plutonium (Pu) isotopic composition (the atom or activity ratios) and activity concentrations of ²³⁸Pu, ²³⁹Pu, ²⁴⁰Pu, and ²⁴¹Pu resulting from the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident in 2011. In this critical review, we document the characteristic values of Pu atom or activity ratios (fingerprints) and present their spatial distributions around the FDNPP site. Based on multiple Pu fingerprints (²³⁸Pu/^239+240Pu activity ratio, ²⁴⁰Pu/²³⁹Pu atom ratio, and ²⁴¹Pu/²³⁹Pu atom ratio), we clarify that Pu contamination from the FDNPP accident occurred in a restricted terrestrial area, while Pu in the Northwest Pacific Ocean is still predominately sourced from the Pacific Proving Grounds (PPG) and global fallout. Using a simple two end-member mixing model, we calculate average contributions of Pu from the FDNPP accident of 13 ± 20% (n = 180) in soil samples, 55 ± 32% (n = 38) in leaf litter samples, and 67 ± 26% (n = 129) in air dust/black substances. In the marine environment, the PPG source average contributions are 45 ± 15% (n = 76) in seawater and 42 ± 12% (n = 48) in sediments. The spatial distributions of Pu atom or activity ratios based on existing studies suggest that: 1) in the terrestrial region investigated 80 km northwest of the FDNPP site, the Pu contamination is mainly observed in an area within a 50 km distance, and 2) in the terrestrial region investigated 60 km southwest of the FDNPP site, the Pu contamination is mainly observed in an area within a 30 km distance. Studies of Cs-bearing radioactive particles indicate that Pu occurs as Pu oxide, and the fuel fragments containing Pu that were released from the reactors to the surrounding environment are associated with micron-scale Cs-bearing radioactive particles. We note that the fractionation between Pu and other radionuclides occurred after release. These new findings about the Pu fingerprints around the FDNPP site will help researchers to establish a reference background database for future environmental risk assessment and geochemical study there.

Source and distribution characteristics of 239, 240, 241Pu, 237Np and 134, 137Cs in sediments in the Northwest and Central Equatorial Pacific after the Fukushima nuclear accident

To understand the possible influence of the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident on the deep sea, as well as the geochemical behavior and transport of radionuclides, ¹³⁴Cs, ¹³⁷Cs, ^{239, 240}Pu, ²⁴¹Pu, and ²³⁷Np were measured in the abyssal sediments of the Northwest Pacific (NWP) and Central Equatorial Pacific (CEP) Ocean. Data on the characteristics of these sediments obtained after the FDNPP accident are extremely rare, especially in the NWP subtropical gyre (NPSG) region. FDNPP-derived radio-Cs (¹³⁴Cs, ¹³⁷Cs) arrived at the open sea floor of the NWP before 2018 but was only found in the Kuroshio-Oyashio Extension (KOE) region. No FDNPP-derived Pu was detected in the abyssal sediments of the NWP or CEP. Pu in the NWP mainly originated from global fallout and the Pacific Proving Ground (PPG) close-in fallout, except for at station WP1 (39°N in the KOE region), where an abnormal but non-FDNPP-derived Pu signal was detected. Pu in the eastern CEP sediment was less affected by the PPG close-in fallout from the Marshall Islands and was mainly derived from global fallout, with some close-in fallout from the Johnston Atoll test. The KOE region was the area most affected by PPG close-in fallout Pu via Kuroshio transport, while the lowest inventories of ^239+240Pu and ²³⁷Np were found in the NPSG region due to its oligotrophic environment. The ²³⁷Np originated from the same source as Pu, and the latitudinal pattern of ²³⁷Np was consistent with that of Pu. Station SS (in the marginal sea of the NWP) contained high ²³⁷Np/²³⁹Pu atom ratios in the deeper layers of sediment and had a ²³⁷Np depth profile opposite that of the ^239+240Pu profile, compared to other stations; these differences are mainly attributed to differences in the behaviors of ²³⁷Np and ²³⁹Pu.

Analysis of particles containing alpha-emitters in stagnant water at torus room of Fukushima Dai-ichi Nuclear Power Station’s Unit 2 reactor

Particles containing alpha (α) nuclides were identified from sediment in stagnant water in the torus room of the Fukushima Dai-ichi Nuclear Power Station(FDiNPS)’s Unit 2 reactor. We analyzed uranium (U), which is the main component of nuclear fuel, using scanning electron microscopy (SEM). Other α-nuclides (plutonium [Pu], americium [Am], and curium [Cm]) were detected by alpha track detection and the morphology of particles with α-nuclides were analyzed by SEM-energy dispersive X-Ray (EDX) analysis. Several uranium-bearing particles ranging from sub-µm to several µm in size were identified by SEM observation. These particles contained zirconium (Zr) and other elements which constituted fuel cladding and structural materials. The 235U/238U isotope ratio in the solid fractions that included U particles was consistent with what was found for the nuclear fuel in the Unit 2 reactor. This indicated that the U of similar fuel composition had made finer. The α-nuclide-containing particles identified by alpha track analysis were several tens to several hundred µm in size. The EDX spectra showed that these particles mainly comprised iron (Fe). Since the amount of α-nuclide material was very small, Pu, Am, and Cm were adsorbed on the Fe particles. This study clarifies that the major morphologies of U and other α-nuclides in the sediment of stagnant water in the torus room of FDiNPS’s Unit 2 reactor differed.

Sources and Variability of Plutonium in Chinese Soils: A Statistical Perspective with Moving Average

We investigated the different sources and their corresponding impact areas of Pu in Chinese surface soils to illustrate the state-of-the-art of the sources, levels and distributions of 240Pu/239Pu atom ratios as well as 239+240Pu activity concentrations in China. For the first time a moving average strategy in combination with statistical analysis was employed to partition geographic areas in China based on the reported 240Pu/239Pu atom ratio and 239+240Pu concentration data from public literature. During the partitioning, the median (MED) of the dataset was basically employed as a criteria in place of the commonly used arithmetic average (AM). Concisely, three areas were partitioned according to the different influences of Pu from the Lop Nor (LNTS) and Semipalatinsk (STS) test sites and the global fallout. The partitioned Ternary area (80° E–105° E, 35° N–50° N) was supposed to have multiple sources of Pu including the STS and LNTS besides the global fallout, which was characterized with slightly lower 240Pu/239Pu atom ratios (MED = 0.174) as well as elevated 239+240Pu concentrations (MED = 0.416 mBq/g). Meanwhile, the Binary area (35° N–45° N, 100° E–115° E) was considered to have received the extra contribution from the high-yield nuclear tests at the LNTS besides the global fallout, resulting in the highest 240Pu/239Pu atom ratios (MED = 0.200) across China. The remaining area was marked as the Unitary area, where it only received the exclusive contribution of global fallout. Furthermore, through the statistical analysis of the 240Pu/239Pu data in the Unitary area, we recommended a value of 0.186 ± 0.021 (AM ± SD) as a representative or area-specific 240Pu/239Pu atom ratio baseline to characterize the global fallout derived Pu in Chinese soils.

A summary of environmental radioactivity research studies by members of the Japan Society of Nuclear and Radiochemical Sciences

Many scientists who are members of the Japan Society of Nuclear and Radiochemical Sciences have been involved in academic activities in response to the Fukushima Daiichi Nuclear Power Plant accident. Projects had been implemented that include determining radionuclides in environmental samples, identifying the distribution of radionuclides by large-scale soil monitoring, tracing radionuclide discharge time series, clarifying environmental dynamics of radionuclides, etc. For the last 10 years, these results have been shared and discussed in annual workshops partly sponsored by the society. This review summarizes the studies yielding these results, and they include reconstruction of the 131I distribution on soil by long-lived 129I analysis, reconstruction of the radioactive plume transport, identification of biological resuspension sources, discovery and characterization of cesium particles, and parameterization of the environmental behavior of radiocesium for dose assessment.

Meteoric 10Be, 137Cs and 239+240Pu as Tracers of Long- and Medium-Term Soil Erosion—A Review

Isotopes of meteoric 10Be, 137Cs, 239+240Pu have been proposed as a soil redistribution tracer and applied worldwide as an alternative method to classical field-related techniques (e.g., sediment traps). Meteoric 10Be provides information about long-term soil redistribution rates (millennia), while 137Cs and 239+240Pu give medium-term rates (decades). A significant progress in developing new models and approaches for the calculation of erosion rates has been made; thus, we provide a global review (n = 59) of research articles to present these three isotopes (meteoric 10Be, 239+240Pu and 137Cs) as soil erosion markers in different environments and under different land-use types. Understanding the dynamics and behaviours of isotopes in the soil environment is crucial to determine their usefulness as soil erosion tracers; thus, we discuss the chemical–physical behaviour of meteoric 10Be, 137Cs and 239+240Pu in soils. The application of these isotopes sometimes has strong limitations, and we give suggestions on how to overcome them or how to adapt them to a given situation. This review also shows where these isotopic methods can potentially be applied in the future. A lack in knowledge about soil redistribution rates exists particularly in loess-dominated areas where the tillage system has changed or in areas with strong wind erosion.

Soil-soil solution distribution coefficients of global fallout 239Pu and 237Np in Japanese paddy soils

²³⁹Pu and ²³⁷Np are long-lived radionuclides that emit alpha rays, and once released into the environment, they are present there for a long period of time. Therefore,²³⁹Pu and ²³⁷Np are important radionuclides in the safety assessment related to geological disposal of radioactive waste because of the possibility of long-term exposure to humans. Mobilities of these radionuclides in the environment are of particular interest; therefore, in this study, we have made the first-time determination of the soil-soil solution distribution coefficient (K_d, L/kg) using global fallout ²³⁹Pu and ²³⁷Np in soil. The K_d values were determined by extracting these radionuclides from 23 soil samples using a laboratory batch method. The desorption K_d values of ²³⁹Pu were found to vary from 3.2 × 10³ to 1.4 × 10⁵ L/kg, and their geometric mean (GM) and arithmetic mean (AM) were 2.3 × 10⁴ L/kg and 3.2 × 10⁴ L/kg, respectively. The desorption K_d values of ²³⁷Np ranged from 8.9 × 10² to 2.1 × 10⁴ L/kg, and their GM and AM were 4.1 × 10³ L/kg and 6.4 × 10³ L/kg, respectively. A comparison between the obtained K_d values of ²³⁹Pu and ²³⁷Np indicated that the former were about 6-fold higher than the latter in Japanese paddy field soils. Pearson's correlation analysis suggested that the main factors contributing to the sorption and desorption of Pu isotopes in Japanese paddy soils were related to the amounts of Fe and Mn oxides, while the sorption and desorption of ²³⁷Np in them would be controlled by an ion-exchange reaction, and/or complex-formation with organic matter, especially in Fluvisols.

Isotopic signatures of plutonium and uranium at Bikar atoll, northern Marshall Islands

We present plutonium (Pu) and uranium (U) isotopic fingerprints (or signatures) in environmental samples collected at Bikar Atoll. Bikar is the second -most northern atoll of the Republic of the Marshall Islands, and therefore an important reference point to evaluate the extension of the regional fallout from the Pacific Proving Grounds (PPG) in Bikini and Enewetak Atolls. Previous studies have shown that regional fallout from atmospheric nuclear weapon testing (NWT) in Bikini and Enewetak has resulted in elevated levels of fallout radionuclides in this atoll. In order to optimally interpret the isotopic fingerprints, we compare our results with data obtained in eleven certified reference materials, representing different contamination sources. As well as ²³⁸Pu, ²³⁹Pu, ²⁴⁰Pu, ²⁴¹Pu, ²³⁸U and ²³⁵U, this study also encompasses less commonly reported radionuclides such as ²⁴²Pu, ²⁴⁴Pu and ²³⁶U. We show the importance of combining numerous fingerprints for improved assessment of the source of a nuclear contamination. In samples from Bikar, Pu and U isotope ratios were found to vary within narrow ranges. Pu and U fingerprints suggest that regional fallout from the Castle Bravo test in March 1954 was the main source of the contamination. This was further confirmed by two different age dating approaches that estimated 1954 as the year of the contamination. We demonstrate that use of an exponential function to approximate the yield of heavy radionuclides in thermonuclear explosions with increasing mass is a valid approach for estimating the age of a contamination. We show that, if sufficient radionuclide activity concentration measurement results with low uncertainties are available, this method is robust.

237Np and 241Am as Fingerprints in the Major River Basins of Southern China and North South China Sea: A Land-Sea Perspective

During the global nuclear weapon tests, large amounts of radioactive elements are released into the environment. Long-period actinide elements such as Np, Pu, and Am exhibit different behaviors in various environments, and their isotope characteristic fingerprints are of great significance for studying the distribution, migration, and prediction of radioactive pollutants. To investigate the distribution of ²⁴¹Am and ²³⁷Np in southern China, activities of ²⁴¹Am (0.008 ± 0.012-0.932 ± 0.066 Bq/kg) and ²³⁷Np (0.037 ± 0.003-1.458 ± 0.063 mBq/kg), ²³⁷Np/²³⁹Pu atom ratios (0.055 ± 0.003-0.864 ± 0.054), and ²⁴¹Am/^239+240Pu activity ratios (0.033 ± 0.075-15.870 ± 0.477) in 95 surface sediment samples collected from the northern South China Sea and major river basins were analyzed for the first time. Due to the different scavenging mechanisms of Am and Pu, ²⁴¹Am is preferentially concentrated by sinking the particulate, while plutonium is scavenged in the coastal area, resulting in a higher ²⁴¹Am/^239+240Pu activity ratio in estuary and coastal areas. The distribution of ²³⁷Np shows obvious spatial inhomogeneity as the high migration rate. The relevant fingerprint characteristic has changed greatly and needs to be updated urgently. As a result of the convergence of land and sea, ²⁴¹Am, ^239,240Pu, and ²³⁷Np are dominated by terrestrial sediments and deposited in the coastal area of southern China, which should be paid more attention to. This work can establish China's current neptunium radioactivity database, and the difference in Np, Pu, and Am scavenging processes may be a powerful tool for evaluating the impact of the Pearl River Estuary salt tide.

Europe-Wide Atmospheric Radionuclide Dispersion by Unprecedented Wildfires in the Chernobyl Exclusion Zone, April 2020

From early April 2020, wildfires raged in the highly contaminated areas around the Chernobyl nuclear power plant (CNPP), Ukraine. For about 4 weeks, the fires spread around and into the Chernobyl exclusion zone (CEZ) and came within a few kilometers of both the CNPP and radioactive waste storage facilities. Wildfires occurred on several occasions throughout the month of April. They were extinguished, but weather conditions and the spread of fires by airborne embers and smoldering fires led to new fires starting at different locations of the CEZ. The forest fires were only completely under control at the beginning of May, thanks to the tireless and incessant work of the firefighters and a period of sustained precipitation. In total, 0.7-1.2 TBq ¹³⁷Cs were released into the atmosphere. Smoke plumes partly spread south and west and contributed to the detection of airborne ¹³⁷Cs over the Ukrainian territory and as far away as Western Europe. The increase in airborne ¹³⁷Cs ranged from several hundred μBq·m^-3 in northern Ukraine to trace levels of a few μBq·m^-3 or even within the usual background level in other European countries. Dispersion modeling determined the plume arrival time and was helpful in the assessment of the possible increase in airborne ¹³⁷Cs concentrations in Europe. Detections of airborne ⁹⁰Sr (emission estimate 345-612 GBq) and Pu (up to 75 GBq, mostly ²⁴¹Pu) were reported from the CEZ. Americium-241 represented only 1.4% of the total source term corresponding to the studied anthropogenic radionuclides but would have contributed up to 80% of the inhalation dose.

Distinctive distribution and migration of global fallout plutonium isotopes in an alpine lake and its implications for sediment dating

This work investigated plutonium (Pu) isotopes in sediment cores collected from an alpine lake (Lake Heinongpo with 3779 m above sea level) in Southwestern China. ²⁴⁰Pu/²³⁹Pu atom ratios in all sediment samples showed the typical global fallout values of ∼0.18 without any influences from other Pu contaminant sources. ^239+240Pu activities with surface and subsurface maximums followed by exponential decline with sediment depth were respectively observed in the two sediment cores. The distinctive depth distributions of ^239,240Pu in the lake sediments was attributed to the very slow sediment deposition rate due to the lack of terrestrial sediment input, while the alpine snowmelt input was the primary source of Pu in the lake sediments in addition to the direct atmospheric deposition. The total Pu inventory was estimated to be 56.3 ± 1.4 and 63.9 ± 0.8 Bq/m² respectively in the two sediment cores. The generally higher Pu inventory in the Lake Heinongpo compared with other reported lakes in similar latitude should be mainly attributed to their different Pu input passages. The advection-diffusion equation was further applied to evaluate the downward migration of Pu isotopes in the sediment cores and predict the future evolution of Pu distribution in the sediment cores. The fitted results indicated that the diffusion effect controlled the downward migration of Pu in the sediments, but this diffusive migration will not prevent the peak of global fallout Pu in undisturbed sediment cores from being a valuable time marker for sediment dating.

Rapid analysis of 237Np and Pu isotopes in small volume urine by SF-ICP-MS and ICP-MS/MS

Internal contamination with alpha-particle emitting actinides, such as ²³⁷Np, ²³⁹Pu, ²⁴⁰Pu, is likely to bring a large amount of dose to the tissues of persons even if the intake amount is small. To provide timely information for prompt decision-making in radiation emergency therapy, we developed a simple and rapid method for urinary bioassay to determine ultra-trace ²³⁷Np and Pu isotopes using SF-ICP-MS and ICP-MS/MS. To avoid polyatomic interferences and tailing effects from U, ²³⁷Np and Pu isotopes were collected after removing U effectively using a simple single chromatographic column packed with 2 mL AG MP-1M anion exchange resin, exhibiting a high decontamination factor of 10⁸ for ²³⁸U. The overall chemical fractionation between ²³⁷Np and ²⁴²Pu for the whole analytical procedure was 0.974 ± 0.064 (k = 2), allowing us to measure ²³⁷Np and Pu isotopes using ²⁴²Pu as a yield tracer with yields of 76 ± 5%. Using ICP-MS/MS with low background provided the method detection limits for ²³⁷Np, ²³⁹Pu, ²⁴⁰Pu, and ²⁴¹Pu of 0.025, 0.025, 0.015, and 0.020 fg mL^-1, respectively, for 20 mL of urine sample. Those were comparable to detection limits of SF-ICP-MS with high sensitivity. Subsequently, three urine reference materials with Pu spike, provided by the Association for the PROmotion of Quality COntrol in RADiotoxicological Analysis (PROCORAD), France, were analyzed by the developed method and the conventional alpha spectrometry technique for validation. Finally, the developed method was successfully employed to measure the contamination level of ²³⁷Np, ²³⁹Pu, ²⁴⁰Pu, and ²⁴¹Pu in urine samples collected during decorporation therapy using DTPA, after a Pu inhalation exposure accident in Japan. The high throughput (9 h for 12 samples), simplicity, low cost, and high sensitivity of the method will allow greater numbers of related laboratories to be involved in screening activities for unexpected actinide exposure, such as in the case of a large scale radiological disaster.

Microbial interaction with and tolerance of radionuclides: underlying mechanisms and biotechnological applications

Radionuclides (RNs) generated by nuclear and civil industries are released in natural ecosystems and may have a hazardous impact on human health and the environment. RN-polluted environments harbour different microbial species that become highly tolerant of these elements through mechanisms including biosorption, biotransformation, biomineralization and intracellular accumulation. Such microbial-RN interaction processes hold biotechnological potential for the design of bioremediation strategies to deal with several contamination problems. This paper, with its multidisciplinary approach, provides a state-of-the-art review of most research endeavours aimed to elucidate how microbes deal with radionuclides and how they tolerate ionizing radiations. In addition, the most recent findings related to new biotechnological applications of microbes in the bioremediation of radionuclides and in the long-term disposal of nuclear wastes are described and discussed.

The mental health status of children who have been evacuated or migrated from rural areas in Fukushima prefecture after the Fukushima daiichi nuclear power station accident:results from the Fukushima health management survey

INTRODUCTION

We evaluated the mental health status of children residing in Kawauchi village (Kawauchi), Fukushima Prefecture, after the 2011 accident at the Fukushima Daiichi Nuclear Power Station, based on the children's experience of the nuclear disaster.

METHODS

We conducted this cross-sectional study within the framework of the Fukushima Health Management Survey (FHMS);FHMS data on age, sex, exercise habits, sleeping times, experience of the nuclear disaster, and the "Strengths and Difficulties Questionnaire (SDQ)" scores for 156 children from Kawauchi in 2012 were collected. Groups with and without experience of the nuclear disaster - "nuclear disaster (+)" and "nuclear disaster (-)" - were also compared.

RESULTS

Our effective response was 93 (59.6%);the mean SDQ score was 11.4±6.8 among elementary school-aged participants and 12.4±6.8 among junior high school-aged ones. We statistically compared the Total Difficulties Scores (TDS) and sub-item scores of the SDQ between "elementary school" and "junior high school" or "nuclear disaster" (+) and (-). There was no significant difference between these items.

CONCLUSIONS

We found indications of poor mental health among elementary and junior high school-aged children in the disaster area immediately following the accident, but no differences based on their experience of the nuclear disaster. These results indicate the possibility of triggering stress, separate to that from experiences related to the nuclear disaster, in children who lived in affected rural areas and were evacuated just after the nuclear disaster.

Differentiating Fukushima and Nagasaki plutonium from global fallout using 241Pu/239Pu atom ratios: Pu vs. Cs uptake and dose to biota

Plutonium (Pu) has been released in Japan by two very different types of nuclear events - the 2011 Fukushima accident and the 1945 detonation of a Pu-core weapon at Nagasaki. Here we report on the use of Accelerator Mass Spectrometry (AMS) methods to distinguish the FDNPP-accident and Nagasaki-detonation Pu from worldwide fallout in soils and biota. The FDNPP-Pu was distinct in local environmental samples through the use of highly sensitive ²⁴¹Pu/²³⁹Pu atom ratios. In contrast, other typically-used Pu measures (²⁴⁰Pu/²³⁹Pu atom ratios, activity concentrations) did not distinguish the FDNPP Pu from background in most 2016 environmental samples. Results indicate the accident contributed new Pu of ~0.4%-2% in the 0-5 cm soils, ~0.3%-3% in earthworms, and ~1%-10% in wild boar near the FDNPP. The uptake of Pu in the boar appears to be relatively uninfluenced by the glassy particle forms of fallout near the FDNPP, whereas the ^134,137Cs uptake appears to be highly influenced. Near Nagasaki, the lasting legacy of Pu is greater with high percentages of Pu sourced from the 1945 detonation (~93% soils, ~88% earthworm, ~96% boar). The Pu at Nagasaki contrasts with that from the FDNPP in having proportionately higher ²³⁹Pu and was distinguished by both ²⁴⁰Pu/²³⁹Pu and ²⁴¹Pu/²³⁹Pu atom ratios. However, compared with the contamination near the Chernobyl accident site, the Pu amounts at all study sites in Japan are orders of magnitude lower. The dose rates from Pu to organisms in the FDNPP and Nagasaki areas, as well as to human consumers of wild boar meat, have been only slightly elevated above background. Our data demonstrate the greater sensitivity of ²⁴¹Pu/²³⁹Pu atom ratios in tracing Pu from nuclear releases and suggest that the Nagasaki-detonation Pu will be distinguishable in the environment for much longer than the FDNPP-accident Pu.

Transuranic nuclides Pu, Am and Cm isotopes, and 90Sr in seafloor sediments off the Fukushima Daiichi Nuclear Power Plant during the period from 2012 to 2019

The ²³⁸Pu, ^239+240Pu, ²⁴¹Am, ²⁴²Cm, ^243+244Cm and ⁹⁰Sr concentrations in seafloor surface sediments collected at three sampling stations off the Fukushima Daiichi Nuclear Power Plant (FDNPP) site during the period from 2012 to 2019 were determined to elucidate the impacts of the FDNPP accident onto their concentrations in coastal sediments and to discuss the sources of the measured radionuclides. The ^239+240Pu, ²⁴¹Pu and ²⁴¹Am concentrations and ²⁴⁰Pu/²³⁹Pu atom ratios in a sediment core were also determined to allow comparison of their inventories between this study and previously reported values and to identify the Pu sources. The ²³⁸Pu, ^239+240Pu, ²⁴¹Am and ⁹⁰Sr concentrations showed no remarkable temporal variations; no significant increases in concentrations after the FDNPP accident were observed; these concentrations were comfortably within the previously reported concentration range; and no detectable ²⁴²Cm and ^243+244Cm amounts were observed in surface sediments. The observed ²³⁸Pu/^239+240Pu activity ratios were approximately two orders of magnitudes lower than those for the damaged FDNPP reactor core inventories and the observed values in terrestrial samples after the accident. The ^239+240Pu, ²⁴¹Pu and ²⁴¹Am inventories in the sediment core were 389 ± 5, 503 ± 33 and 214 ± 3 Bq m^-2, respectively. The ^239+240Pu inventory was about an order of magnitude greater than the expected cumulative deposition density of global fallout from atmospheric nuclear weapons testing due to an enhanced scavenging effect. The ²⁴⁰Pu/²³⁹Pu atom ratios in the sediment core ranged from 0.239 to 0.246 with a mean value of 0.242 ± 0.002; these ratios were clearly greater than the mean global fallout ratio of 0.18. The results for ²³⁸Pu/^239+240Pu activity ratios and ²⁴⁰Pu/²³⁹Pu atom ratios reflected a mixture of global fallout and Pacific Proving Grounds (PPG) close-in fallout Pu rather than Fukushima accident-derived Pu. The sediment column inventory for ^239+240Pu originating from the PPG close-in fallout was calculated as 166 Bq m^-2, which corresponded to 43% of the total inventory. A significant amount of the PPG-derived Pu has been transported by ocean currents and then preferentially scavenged in the coastal waters of Japan.

Matrix-Assisted Ionization of Molecular Uranium Species

Matrix-assisted ionization (MAI) demonstrates high sensitivity for a variety of organic compounds; however, few studies have reported the application of MAI for the detection and characterization of inorganic analytes. Trace-level uranium analysis is important in the realms of nuclear forensics, nuclear safeguards, and environmental monitoring. Traditional mass spectrometry methods employed in these fields require combinations of extensive laboratory chemistry sample preparation and destructive ionization methods. There has been recent interest in exploring ambient mass spectrometry methods that enable timely sample analysis and higher sensitivity than what is attainable by field-portable radiation detectors. Rapid characterization of uranium at nanogram levels is demonstrated in this study using MAI techniques. Mass spectra were collected on an atmospheric pressure mass spectrometer for solutions of uranyl nitrate, uranyl chloride, uranyl acetate, and uranyl oxalate utilizing 3-nibrobenzonitrile as the ionization matrix. The uranyl complexes investigated were detectable, and the chemical speciation was preserved. Sample analysis was accomplished in a matter of seconds, and limits of detection of 5 ng of uranyl nitrate, 10 ng of uranyl oxalate, 100 ng of uranyl chloride, and 200 ng of uranyl acetate were achieved. The observed gas-phase speciation was similar to negative-ion electrospray ionization of uranyl compounds with notable differences. Six matrix-derived ions were detected in all negative-ion mass spectra, and some of these ions formed adducts with the uranyl analyte. Subsequent analysis of the matrix suggests that these molecules are not matrix contaminants and are instead created during the ionization process.

Distribution of Pu isotopes and 210Pb in the Bohai Sea and Yellow Sea: Implications for provenance and transportation

Particle-reactive radionuclides are useful for tracing sediment dynamics in marginal seas. We collected a suite of surface sediment samples in May 2014 from the Bohai Sea (BS) and Northern Yellow Sea (NYS) to observe the spatial distribution of Plutonium (Pu) isotopes and ²¹⁰Pb activities. ^239+240Pu activities ranged from 0.001 to 0.288 and 0.040-0.269 Bq kg^-1 in BS and NYS surface sediments, respectively. ²¹⁰Pb_ex shows a significant correlation with ^239+240Pu (r = 0.84, p < 0.01) that suggested these two nuclides were scavenged to the same grade. ²⁴⁰Pu/²³⁹Pu atom ratios in BS (0.173-0.256) and NYS (0.196-0.275) were slightly higher than the global fallout value of 0.18 and lower than the Pacific Proving Ground (PPG) value of 0.36, indicating that some fraction of Pu originating from the PPG was capable of being transported to the BS and NYS. Mass balance results showed that 41% of ^239+240Pu (8.9 × 10⁹ Bq yr^-1) and 18% of ²¹⁰Pb (2.4 × 10¹² Bq yr^-1) in the NYS originated in the oceanic input. In the BS, 63% of ²¹⁰Pb originated from atmospheric deposition and 84% of ^239+240Pu originated from riverine input. Using Pu and ²¹⁰Pb as tracers, we estimate that (1.8-2.6) × 10⁸ t yr^-1 and (3.6-3.8) × 10⁸ t yr^-1 of sedimentary particles could be transported from the BS to the NYS and from the NYS to the Southern Yellow Sea, respectively. Furthermore, the ²²⁶Ra/²³⁸U activity ratio distribution suggested that sedimentary particles derived from the Yellow River could be transported to the middle of the BS and coastal areas of the NYS.

Innovative high-temperature ammonium bifluoride fusion and rapid analysis of elements with nuclear forensic value

High-temperature ammonium bifluoride (ABF) fusions were evaluated for potential use in rapid dissolution of post-detonation nuclear debris. The ABF fusion was carried out in a Pt crucible which allowed evaluation of higher fusion and evaporation temperatures. The high-temperature ABF fusion dissolution method was evaluated using geological reference materials: USGS QLO-1a Quartz Latite, USGS SDC-1 Mica Schist, and NIST 278 Obsidian Rock. The optimized dissolution method involved a 10 min fusion at 540 °C, a 5 min reflux in 8 M HNO_3, an evaporation at 300 °C and final dilution into 45 mL of 2% (v/v) HNO₃. The final solution was filtered after heating at 105 °C using a hotblock. This dissolution method was simple, requiring only a hotplate or hotblock, filtered samples were available for ICP-MS analysis or radiochemical separation within 150 min, and was found to have high (>90%) recovery for many isotopes of interest in nuclear forensics applications. U and Pu in the dissolved material was separated using TEVA and UTEVA extraction chromatography columns, a process which resulted in >90% recovery. An irradiated U tracer was spiked into the material prior to dissolution and analyzed for recovery of major fission products and ²³⁹Np. The monitored radionuclides had recoveries of greater than 90%, except for the volatile radioiodine isotopes.

Particulate plutonium released from the Fukushima Daiichi meltdowns

Traces of Pu have been detected in material released from the Fukushima Daiichi Nuclear Power Plant (FDNPP) in March of 2011; however, to date the physical and chemical form of the Pu have remained unknown. Here we report the discovery of particulate Pu associated with cesium-rich microparticles (CsMPs) that formed in and were released from the reactors during the FDNPP meltdowns. The Cs-pollucite-based CsMP contained discrete U(IV)O₂ nanoparticles, <~10 nm, one of which is enriched in Pu adjacent to fragments of Zr-cladding. The isotope ratios, ²³⁵U/²³⁸U, ²⁴⁰Pu/²³⁹Pu, and ²⁴²Pu/²³⁹Pu, of the CsMPs were determined to be ~0.0193, ~0.347, and ~0.065, respectively, which are consistent with the calculated isotopic ratios of irradiated-fuel fragments. Thus, considering the regional distribution of CsMPs, the long-distance dispersion of Pu from FNDPP is attributed to the transport by CsMPs that have incorporated nanoscale fuel fragments prior to their dispersion up to 230 km away from the Fukushima Daiichi reactor site.

Plutonium in Southern Yellow Sea sediments and its implications for the quantification of oceanic-derived mercury and zinc

The spatial distributions of mercury (Hg) and zinc (Zn) concentration and the isotopic composition of plutonium (Pu) were investigated in surface sediments and sediment cores collected from the Southern Yellow Sea (SYS) during May 2014. The variation of the ²⁴⁰Pu/²³⁹Pu atom ratio (0.18-0.31) in the surface sediments of the SYS clearly indicated a signal of close-in fallout input from the Pacific Proving Ground (PPG). The buried ^239+240Pu in the sediment of the SYS was estimated to be (4.7 ± 0.5) × 10¹⁰ Bq y^-1 during the period from 2011 to 2014, of which ∼33% (1.5 × 10¹⁰ Bq y^-1) was derived from the PPG by long-range transport via ocean currents (e.g., the North Equatorial Current and Kuroshio Current). The concentrations of Hg and Zn varied from 0.003 to 0.067 mg kg^-1 and from 43.9 to 137 mg kg^-1, respectively, and exhibited positive correlations with the ^239+240Pu activity both in the surface sediments (0-1 cm) and upper layers (7 cm) of the sediment cores. Therefore, by using Pu as a tracer, we estimated that the oceanic input contributed 2.0 tons y^-1 of Hg and 1.0 × 10³ tons y^-1 of Zn to the SYS sediments between 2011 and 2014, which accounted for 33% and 3% of total buried Hg and Zn, respectively. These findings indicate that environmental pollution control should also consider the oceanic contribution of some pollutants. The results of the present work help to elucidate the biogeochemical cycling of trace metals in marginal seas, and are helpful for managing environmental pollution in marine environments.

Initiation of radioecological monitoring of forest soils and plants at the Lithuanian border region before the start of the Belarusian nuclear power plant operation

Knowledge of the background activity concentrations of anthropogenic radionuclides before the start of operation of the new nuclear power plant in Belarus, BelNPP, is an issue of great importance for neighbouring countries. In this study, we provide the pilot characterisation of the Lithuanian part of the 30-km zone of the BelNPP, emphasising the forest plants, terrestrial mosses, forest organic and mineral topsoil to describe the preoperational radioecological state of the pine forest ecosystem. Key anthropogenic radionuclides (¹⁴C, ³H, ¹³⁷Cs and ^239,240Pu) were analysed. The ¹⁴C specific activity varied from 97.80 ± 1.30 to 102.40 ± 0.79 pMC. The ³H specific activity in the tissue-free water tritium form varied from 13.2 ± 2.2 TU to 20.8 ± 2.3 TU, which corresponded to the ³H level of precipitation in this region. The activity concentrations of ^239,240Pu in soil and moss samples did not exceed 1 Bq/kg and were mainly due to global fallout after nuclear tests. The ¹³⁷Cs inventory in the pine forest soils of the Lithuanian part of the BelNPP 30-km zone varied from 930 ± 70 to 1650 ± 430 Bq/m². High variation of the inventory and uneven distribution in the soil profile conditioned a wide range of ¹³⁷Сs activity in terrestrial plants from 1.0 ± 0.5 to 40.5 ± 1.8 Bq/kg dry weight. The abundance of microorganisms in different seasons and soil depths do not exceed the natural levels. According to PCA loads, the number of microorganisms and variability of ¹³⁷Cs specific activity is determined by soil abiotic parameters.

Plutonium isotopes in Northern Xinjiang, China: Level, distribution, sources and their contributions

Plutonium in the environment has drawn significant attentions due to its radiotoxicity in high concentration and source term linked with nuclear accidents and contaminations. The isotopic ratio of plutonium is source dependent and can be used as a fingerprint to discriminate the sources of radioactive contaminant. ²³⁹Pu, ²⁴⁰Pu and ¹³⁷Cs in surface soil and soil cores collected from Northern Xinjiang were determined in this work. The concentrations of ^239,240Pu and ¹³⁷Cs are in the range of 0.06-1.20 Bq kg^-1, and <1.0-31.4 Bq kg^-1 (decay corrected to Sep. 2017), respectively, falling in the ranges of global fallout in this latitude zone. The ²⁴⁰Pu/²³⁹Pu atomic ratios of 0.118-0.209 and ^239,240Pu/¹³⁷Cs activity ratios of 0.039-0.215 were measured. Among the investigated sites, distinctly lower ²⁴⁰Pu/²³⁹Pu atomic ratios of 0.118-0.133 and higher ^239,240Pu/¹³⁷Cs activity ratios of 0.065-0.215 compared to the global fallout values were observed in the northwest part, indicating a significant contribution from other source besides the global fallout. This extra source is mainly attributed to the releases of atmospheric nuclear weapons testing at Semipalatinsk Nuclear Test Site, which was transported by the west and northwest wind through the river valley among mountains in this region. This contribution is estimated to account for 28-43% of the global fallout in the northwest part of Northern Xinjiang. The contribution from the Chinese atmospheric nuclear weapons testing to this region is negligible due to the lack of appropriate wind direction to transport the radioactive releases to this region.

First study of 237Np in Chinese soils: Source, distribution and mobility in comparison with plutonium isotopes

In this study, the distribution and migration of ²³⁷Np and ^239+240Pu in soils in the vicinity (<5 km) of Qinshan and Tianwan Nuclear Power Plants in China were studied, which is the first specific study of global fallout ²³⁷Np in Chinese soils. The ²³⁷Np and ^239+240Pu concentrations in surface soils showed large spatial inhomogeneity. A remarkable ^239+240Pu concentration (4.783 mBq/g) was observed in a surface soil near Qinshan NPP and stands for the ever reported highest value in the Chinese soils. The inventories of ^239+240Pu in two Qinshan and Tianwan soil cores were estimated to be 128.8 Bq/m² and 121.0 Bq/m², respectively; while the ²³⁷Np inventories were 0.039 Bq/m² and 0.035 Bq/m² at these sites, respectively. The ²⁴⁰Pu/²³⁹Pu atomic ratios in these soils indicated that the global fallout is the main source of Pu in these regions. However, the non-isotopic ²³⁷Np/²³⁹Pu atomic ratio in environmental soil is not a sensitive indicator for source identification. Furthermore, we conducted pilot study on the migration behaviors of ²³⁷Np and ^239+240Pu in soil core at Qinshan site with the Convection-Dispersion Equation (CDE) model. The obtained apparent dispersion coefficients of ²³⁷Np (2.82 ± 2.06 cm²/y) was 5 times higher than that of ^239+240Pu (0.57 ± 0.16 cm²/y), proving that ²³⁷Np has stronger migration ability than Pu isotopes in the Qinshan soil. Finally, we predicted that with the increase of migration time, both ²³⁷Np and ^239+240Pu concentration in the soil will gradually become more evenly distributed among different soil layers due to the dominant dispersion effects.