Search

The data set “Spatial radionuclide deposition data from the 60 radial km area around the Chernobyl nuclear power plant: results from a sampling survey in 1987” is the latest in a series of data to be published by the Environmental Information Data Centre (EIDC) describing samples collected and analysed following the Chernobyl Nuclear Power Plant accident in 1986. The data result from a survey carried out by the Ukrainian Institute of Agricultural Radiology (UIAR) in April and May 1987 and includes sample site information, dose rate, radionuclide (zirconium-95, niobium-95, ruthenium-106, caesium-134, caesium-137 and cerium-144) deposition, and exchangeable (determined following 1M NH4Ac extraction of soils) caesium-134 and 137. The purpose of this paper is to describe the available data and methodology used for sample collection, sample preparation and analysis. The data will be useful in reconstructing doses to human and wildlife populations, answering the current lack of scientific consensus on the effects of radiation on wildlife in the Chernobyl Exclusion Zone and evaluating future management options for the Chernobyl-impacted areas of Ukraine and Belarus. The data and supporting documentation are freely available from the EIDC under the terms and conditions of the Open Government Licence (Kashparov et al., 2019; https://doi.org/10.5285/a408ac9d-763e-4f4c-ba72-73bc2d1f596d).

Dose estimation for workers and the public was conducted to use the recycled soil removed from the Fukushima prefecture for land reclamation. The land was availed to the public as a greenery-covered area. In the case of revegetation with trees, the absorption of Cs by the trees was considered. The exposure from trees, trimmed or thinned trees, and the organic deposits from litter fall were evaluated. From the results, the concentration levels of radiocesium, 134Cs and 137Cs, for which the annual effective exposure dose does not exceed 1 mSv/y was calculated. Moreover, the thickness of the cover soil required to maintain the exposure dose lower than 10 μSv/y for the public during servicing was ascertained. Furthermore, disasters were considered; for instance, by considering that tsunamis, fires, and intense heavy rain can increase the exposure doses based on the changes in the conditions of the reclamation land. We confirmed that the additional exposure dose during the disaster and rehabilitation of the area was lower than 1 mSv/y. From these evaluation results, we determined the amenable concentration levels for recycling.

In order to study the possibility of removing radioactive cesium (Cs),134Cs and 137Cs, accumulated on the soil surface, a column device of Cs-contaminated soil overlaid on non-contaminated soil was constructed. The movement and distribution of radioactive Cs in soil by pouring various solutions were analyzed with an imaging plate. Further analysis of the chemical composition of the droplets from the device and in the soil after the experiment was reported to investigate the effects of the soil. It was found that most radioactive Cs are effectively transferred by acidic solutions such as 2 M citric acid and 10% polyphosphoric acid, and the impact on soil is not so great.

This paper describes the calculation of the response of the most common types of radiation detectors that were used within the first few weeks after the Chernobyl accident to determine the activity of 131I in the thyroids of Belarusian subjects of an epidemiologic study of thyroid cancer. The radiation detectors, which were placed against the necks of the subjects, measured the exposure rates due to the emission of gamma rays resulting from the radioactive decay of 131I in their thyroids. Because of the external and internal radioactive contamination of the monitored subjects, gamma radiation from many radionuclides in various locations contributed to the exposure rates recorded by the detectors. To estimate accurately the contribution from gamma rays emitted from various internal and external parts of the body, the calibration factors of the radiation detectors, expressed in kBq per µR h− 1, were calculated, by means of Monte Carlo simulation, for external irradiation from unit activities of 17 radionuclides located on 19 parts of the body, as well as for internal irradiation from the same 17 radionuclides in the lungs, from caesium radionuclides distributed uniformly in the whole body, and from 131I in the thyroid. The calculations were performed for six body sizes, representative of the age range of the subjects. In a companion paper, the levels of external and internal contamination of the body were estimated for a variety of exposure conditions. The results presented in the two papers were combined to calculate the 131I activities in the thyroids of all 11,732 Belarusian study subjects of an epidemiologic study of thyroid cancer and, in turn, their thyroid doses.

Ten years have elapsed since the accident at the Fukushima Daiichi Nuclear Power Plant in 2011, and the relative contribution of natural radiation is increasing in Fukushima Prefecture due to the reduced dose of artificial radiation. In order to accurately determine the effective dose of exposure to artificial radiation, it is necessary to evaluate the effective dose of natural as well as artificial components. In this study, we measured the gamma-ray pulse-height distribution over the accessible area of Namie Town, Fukushima Prefecture, and evaluated the annual effective dose of external exposure by distinguishing between natural and artificial radionuclides. The estimated median (range) of absorbed dose rates in air from artificial radionuclides as of 1 April 2020, is 133 (67&ndash, 511) nGy h&minus, 1 in the evacuation order cancellation zone, and 1306 (892&ndash, 2081) nGy h&minus, 1 in the difficult-to-return zone. The median annual effective doses of external exposures from natural and artificial radionuclides were found to be 0.19 and 0.40 mSv in the evacuation order cancellation zone, and 0.25 and 3.9 mSv in the difficult-to-return zone. The latest annual effective dose of external exposure discriminated into natural and artificial radionuclides is expected to be utilized for radiation risk communication.

Sedimentary cesium-137 concentrations around the Fukushima Daiichi Nuclear Power Plant (FDNPP) were measured from 2011 to 2017 at eight stations. Although high values were observed until 2013, decreasing trends were observed at the surface sediments of seven stations. We isolated 25 radioactive Cs-bearing microparticles (CsMPs; 1.0–5385 Bq per particle). The contribution ratio of CsMPs to each sample ranged from 4.1% to 99.5% (median 58.8%), with the contribution ratio of the CsMPs in the southern part of the FDNPP was low compared to that from the northern part. In the southern part of the FDNPP, small CsMPs that could not be isolated in this study were present in large quantities immediately after the accident, and gradually diffused away and/or were dissolved over time. In contrast, the CsMPs in the northern part of the FDNPP have most likely accumulated over time, as suggested by the silty nature of the sediments there.

Gamma spectrometry has been used to evaluate the burnup and fission product inventory of different components from the US Advanced Gas Reactor Fuel Development and Qualification Program’s second TRISO-coated particle fuel irradiation test (AGR-2). TRISO fuel in this irradiation included both uranium carbide/uranium oxide (UCO) kernels and uranium oxide (UO 2 ) kernels. Four of the 6 capsules contained fuel from the US Advanced Gas Reactor program, and only those capsules will be discussed in this work. The inventories of gamma-emitting fission products from the fuel compacts, graphite compact holders, graphite spacers and test capsule shell were evaluated. The measured activities were used to calculate the fractional release of fission products such as Cs-137, Cs-134, Eu-154, Ce-144, and Ag-110m from the compacts. The fraction of Ag-110m retained in the compacts ranged from 1.8% to full retention. Additionally, the activities of the radioactive cesium isotopes (Cs-134 and Cs-137) have been used to evaluate the burnup of all US TRISO fuel compacts in the irradiation. The experimental burnup evaluations compare favorably with burnups predicted from physics simulations. Predicted burnups for UCO compacts range from 7.26 to 13.15% fission per initial metal atom (FIMA) and 9.01–10.69% FIMA for UO 2 compacts. Measured burnup ranged from 7.3 to 13.1% FIMA for UCO compacts and 8.5–10.6% FIMA for UO 2 compacts. Results from gamma emission computed tomography performed on compacts and graphite holders that reveal the distribution of different fission products in a component will also be discussed. Gamma tomography of graphite holders was also used to locate the position of TRISO fuel particles suspected of having silicon carbide layer failures that lead to in-pile cesium release.

Radiocesium-bearing microparticles (CsMPs) with a diameter and 137Cs radioactivity less than 0.5 µm and 0.05 Bq, respectively, released by the Fukushima nuclear accident were identified on the grou...

Immediately after the Fukushima nuclear power plant accident, a team of 40-50 researchers at the Graduate School of Agricultural and Life Sciences at the University of Tokyo began to analyze the behavior of radioactive materials in the fallout regions. The fallout has remained in situ and become strongly adsorbed within the soil over time. 137Cs was found to bind strongly to the fine clay, weathered biotite, and organic matter in the soil; therefore, it has not mobilized from mountainous regions, even after heavy rainfall. In farmland, the quantity of 137Cs in the soil absorbed by crop plants was small. The downward migration of 137Cs in soil is now estimated at 1-2 mm/year. The intake of 137Cs by trees occurred through the bark and not from the roots. This report summarizes the findings of research across a wide variety of agricultural specialties.

Several reactors at the Fukushima Dai-ichi Nuclear Power Plant suffered damage on March 11, 2011, resulting in the release of radiocesium (134Cs and 137Cs), as well as other radionuclides, into the atmosphere. A week later, these isotopes were detected in aerosols over the state of Hawai'i and in milk samples analyzed on the island of Hawai'i. This study estimated the magnitude of cesium deposition in soil, collected in 2015-2016, resulting from atmospheric fallout. It also examined the patterns of cesium wet deposition with precipitation observed on O'ahu and the island of Hawai'i following the disaster. Fukushima-derived fallout was differentiated from historic nuclear weapons testing fallout by the presence of 134Cs and the assumption that the 134Cs to 137Cs ratio was 1:1. Detectable, Fukushima-derived 134Cs inventories ranged from 30 to 630 Bq m-2 and 137Cs inventories ranged from 20 to 2200 Bq m-2. Fukushima-derived cesium inventories in soils were related to precipitation gradients, particularly in areas where rainfall exceeded 200 mm between March 19 and April 4, 2011. This research confirmed and quantified the presence of Fukushima-derived fallout in the state of Hawai'i in amounts higher than predicted by models and observed in the United States mainland, however the activities detected were an order of magnitude lower than fallout associated with historic sources such as the nuclear weapons testing in the Pacific. In addition, this study showed that areas of highest cesium deposition do not overlap with densely populated or agriculturally used areas.

© 2017 Elsevier Inc. Experimental nuclear structure data from various reactions and decays are compiled and evaluated for all known nuclides with mass number A=138 (Sn,Sb,Te,I,Xe,Cs,Ba,La,Ce,Pr,Nd,Pm,Sm,Eu,Gd,Tb). Detailed evaluated nuclear structure information is presented for each reaction and decay and the best values combining all available data are recommended for level energies, half-lives, γ-ray energies and intensities, decay properties (energies, intensities and placement of radiations), and other spectroscopic properties. This work supersedes the previous full evaluation of A=138 by A.A. Sonzogni (2003So13).

Radioactivity of spent nuclear fuel (SNF) discharged from nuclear reactor core is determined during the first 100 years by fission fragments (FF), after that the main contribution in the SNF activity is made by actinides. Existing scenarios of SNF handling are based on the transmutation of minor actinides (MA) into fission fragments accomplished in fast reactors. Scenarios of transmutation of fission fragments in thermal and fast neutron spectra and time-dependent radiation characteristics are examined in the present study. Nuclide composition of fission fragments is taken from the results of simulation of burnup of 439GT fuel assembly (TVSA type) for VVER-1000 nuclear reactor during 3 years performed using MCU-5 software complex. The obtained data were used for determining starting nuclide composition for different cooling-down times prior to the beginning of transmutation (irradiation in neutron fluxes) to be input in the ORIGEN2 code. The following three options of irradiation of fission fragments are presented: transmutation without cooling down, cooling down fission fragments during 4 years prior to irradiation, cooling down fission fragments during 30 prior to irradiation. Duration of irradiation was selected to be equal to 3 and 15 years. Efficiency of transmutation was determined using time-dependent “transmutation factor” equal to the ratio of radioactivity of nuclides in the process of transmutation and after its completion to their radioactivity without transmutation. The calculated values of transmutation factors proved to be noticeable only during irradiation in reactor core: these values reached 5–10 and were dependent only on the duration of fission fragment cooling down prior to the beginning of transmutation. After removal of fission fragments from neutron flux transmutation factor decreased to unity within several years. After one hundred more years after irradiation in neutron spectrum of thermal reactor transmutation factor reduces to 0.8–0.5 depending on the duration of the transmutation process. Slight growth of transmutation factor to the values of 1.2–1.8 was observed after irradiation in fast reactor spectrum within the time interval of 200–1000 years and after 1000 years following this its reduction to the value of 0.9–0.7 was noted. The main conclusion is that purposeful incineration of fission fragments is senseless because only insignificant gain in radioactivity (a little less than by the factor two) is achieved after 1000 years. The indifference of fission fragments with regard to transmutation can be partially explained by the fraction of stable nuclides which increases with extension of the period of fission fragments cooling down. Upon completion of the cycle of fuel use it contains approximately 15% of stable nuclides among fission fragments, and after 30 years of cooling down the fraction of stable isotopes reaches 85%.

The activity concentrations of naturally occurring radionuclides (such as 226Ra, 210Pb and 210Po) and long lived 137Cs were measured in a total of 119 tissue samples (43 blubber, 43 liver, and 33 muscle samples) from 40 ringed seals and 4 bearded seals collected in the Arviat area of Canada during the fall of 2014. Activity concentration of 210Po was measured in all seal liver and muscle samples individually. The average 210Po activity concentrations were 25 ± 7.6 Bq/kg fresh weight (fw) in muscle and 211 ± 58 Bq/kg fw in liver for ringed seals, and 20 ± 6.1 Bq/kg fw in muscle and 231 ± 150 Bq/kg fw in liver for bearded seals. Due to insufficient sample material for most samples collected, gamma counting for radioactive caesium and radiochemical analysis for 226Ra and 210Pb were performed for pooled samples. Activity concentrations of 210Pb and 226Ra were generally below detection limits. While 134Cs activity concentration was not detectable, 137Cs activity concentration was detected in muscle and liver samples. On average, the 137Cs activity concentrations were 0.25 ± 0.05 and 0.12 ± 0.04 Bq/kg fw in muscle and liver samples of ringed seals, and 0.11 ± 0.02 and 0.10 ± 0.03 Bq/kg fw in muscle and liver samples of bearded seals, respectively. Neither 210Po nor 137Cs were detected in the blubber samples. This study confirmed that 210Po is the dominant contributor to radiation doses resulting from seal consumption. Man-made contaminant 137Cs only contributes less than 0.01% of the total ingestion dose obtained from Arviat seals.

This review summarizes the more than 70 papers published during the 4 years since the Fukushima Dai-ichi nuclear power plant accident that occurred on 11 March 2011, and details the radioactive cesium dispersion pattern in the North Pacific and adjacent seas. The total amount of Fukushima-derived radioactive cesium released into the North Pacific via atmospheric deposition and direct release, spatial and temporal changes in the Pacific coast around the accident site, and the concentration levels of radioactive cesium around the Japanese Islands, not only the Pacific coast but also in adjacent seas, such as Japan Sea, East China Sea are summarized. Based on observational data mostly obtained during 2 years since the accident, and simulation results, oceanic dispersion of radioactive cesium in the entire area of the North Pacific is described. The Fukushima-derived radioactive cesium dispersed eastward as surface water and extended to the eastern side of the North Pacific in 2014, and was also observed via a southward intrusion to subsurface waters as Subtropical Mode Water and Central Mode Water. The radioactive cesium movement related to mode water is important in terms of the circulation of cesium into the ocean interior. Some new technologies and techniques concerning emergency monitoring of radioactivity in the ocean environment are also reported, the effectiveness of which has been demonstrated by use in relation to the Fukushima accident.

Air concentrations of 133Xe, 131I, 132I, 133I, 132Te, 134Cs, 136Cs, and 137Cs in the early stage of the Fukushima Daiichi Nuclear Power Station (FNPS1) accident were estimated for six locations in Ibaraki Prefecture from pulse height distributions measured with NaI(Tl) scintillation detectors continuously operated as a part of monitoring station systems. Air concentration of 133Xe in Ibaraki was estimated for the first time, which showed the maximum value of 150 kBq m−3 in the plume arrived at the southern part of Ibaraki around noon of 15 March 2011. The plume was found to consist mainly of noble gases without other nuclides at significant level and to correspond to the hydrogen explosion at Unit 3. Spatiotemporal distributions of 131I and other nuclides were discussed for the plumes detected during the periods of 15–16 and 20–21 March. Variations in radionuclide composition among the plumes and within each plume were also discussed.

We have proposed a new selective isotope transmutation method using photonuclear reactions with quasi-monochromatic γ-ray beams. This method is based on the fact that the particle threshold of a long-lived fission product (LLFP) such as 93Zr, 107Pd, or 79Se is lower than those of stable isotopes of the same chemical element. Therefore, this method has the excellent advantage that LLFPs cannot, in principle, be produced newly even if the target materials include stable isotopes in addition to LLFPs. Furthermore, this method is effective for 126Sn, 135, 137Cs, 90Sr, and 3H. The nuclear data involved and suitable γ-ray sources are discussed. Laser Compton scattering γ-ray sources and neutron capture γ-rays in nuclear reactors are candidates for this method.

Scientists face challenge in identifying the radioactive materials which are found as dotted images on various imaging plate (IP) autoradiographic photos of radioactively contaminated materials by the Fukushima Dai-ichi Nuclear Power Plant (F1NPP, or FDNPP) accident, such as air filter, fugitive dust, surface soil, agricultural materials, and water-shed samples. It has been revealed that they are minute particles with distinct morphology and elemental composition with high specific radioactivity, and different from those of the so-called Chernobyl hot particles. Basically, they are glassy particles once molten, composed of Si, O, Fe, Zn etc. with highly concentrated radiocaesium, which can be called as radiocaesium-bearing microparticles (CsMP). At present, CsMP can be classified into two types, Types-A and -B, which are characterized by different specific radioactivity, 134Cs/137Cs ratio, size and morphology, and geographic distribution around F1NPP. Such studies on the CsMP from various aspects have provided valuable information about what happened in the nuclear reactors during the F1NPP accident and fates of the CsMP in the environment. This review first provides a retrospective view on the research history of the CsMP, which is helpful to understand the unique character of the CsMP. Subsequently, more details about the current understanding of the natures of these hot particles, such as origin, morphology, chemical compositions, thermal properties, water-solubility, and secondary migration of CsMP in river and ocean systems are described with future prospects.

The time-integrated absorbed dose to the thyroid gland in the years after a fallout event can indicate the potential excess number of thyroid cancers among young individuals after a radionuclide release. Typical mean values of the absorbed dose to the thyroid have been calculated previously using reported data on radioiodine obtained from air sampling and dairy milk surveys in Sweden after the Chernobyl fallout, not including the contribution from Cs-134 and Cs-137. We have developed a model for Swedish conditions taking these additional dose contributions into account. Our estimate of the average time-integrated absorbed dose to the thyroid, D-th,D-tot, during the first 5 years after fallout ranged from 0.5-4.1 mGy for infants and from 0.3-3.3 mGy for adults. The contribution to D-th,D-tot, from I-131 through inhalation and milk consumption varied considerably among different regions of Sweden, ranging from 9%-79% in infants, and from 4%-58% in adults. The external irradiation and exposure from the ingestion of (CS)-C-134,137 in foodstuffs accounted for the remaining contributions to D-th,D-tot, (i.e. up to 96% for adults). These large variations can be explained by the highly diverse conditions in the regions studied, such as different degrees of fractionation between wet and dry deposition, different grazing restrictions on dairy cattle, and differences in (CS)-C-134,137 transfers through food resulting from differences in the local fallout. It is our conclusion that the main contribution to D-th,D-tot, from nuclear power plant fallout in areas subjected to predominantly wet deposition will be from external exposure from ground deposition, followed by internal exposure from contaminated food containing the long-lived fission product Cs-137 and the neutron-activated fission product (CS)-C-134. The contribution from (CS)-C-134,137 to the thyroid absorbed dose should thus be taken into account in future epidemiological studies. Correction in: JOURNAL OF RADIOLOGICAL PROTECTION, Volume: 39, Issue: 3, Pages: 987-989, DOI: 10.1088/1361-6498/ab21ea

Results obtained from a dedicated radiochemistry cruise approximately 100 days after the 11 March 2011 Tohoku earthquake and subsequent disaster at the Fukushima Daiichi Nuclear Power Plant show that Fukushima derived radionuclides in the nearby ocean environment had penetrated, on average, to ≤250 m depth (1026.5 kg m3 potential density surface). The excess inventory of Fukushima-derived 129I in the region (∼150 000 km2) sampled during the cruise is estimated to have been between 0.89 and 1.173 billion Bq (∼136 to ∼179 grams) of 129I. Based on a tight tracer–tracer relation with 134Cs (or 137Cs) and estimates that most of the excess cesium is due to direct discharge, we infer that much of the excess 129I is from direct (non-atmospheric deposition) discharge. After taking into account oceanic transport, we estimate the direct discharge, i.e., that directly released into the ocean, off Fukushima to have been ∼1 kg 129I. Although this small pulse is dwarfed by the ~90 kg of weapons-testing-derived 129I that was released into the environment in the late 1950s and early 1960s, it should be possible to use Fukushima-derived 129I and other radionuclides (e.g., 134, 137Cs) to study transport and entrainment processes along and across the Kuroshio Current.

Approximately two months after the Fukushima nuclear accident, the Japan Atomic Energy Agency (JAEA) led off a series of demonstration tests to develop effective but easily applicable decontamination methods for various school facilities in Fukushima. This effort included (1) dose reduction measures in schoolyards, (2) purification of swimming pool water, and (3) removal of surface contamination from playground equipment. Through these demonstration tests, they established practical methods suitable for each situation: (1) In schoolyards, dose rates were drastically reduced by removing topsoil, which was then placed in 1-m-deep trenches at a corner of the schoolyard. (2) For the purification of pool water, the flocculation coagulation treatment was found to be effective for collecting radiocesium dissolved in the water. (3) Demonstration tests for playground equipment, such as horizontal bars and a sandbox wood frame indicated that the decontamination effectiveness considerably varied depending on the material, paint or coating condition of each equipment piece. These findings were summarized in reports, some of which were compiled in local/national guidelines or handbooks for decontaminating the living environment in Fukushima.

In the current study, 32 brands of canned tuna that were purchased in supermarkets in Riyadh, Saudi Arabia were analysed to quantify the activity levels of 137Cs, 134Cs and 40K. These samples were processed in Japan, the Philippines, Thailand, Europe and the Middle East in 2011 and 2012. The samples were analysed using high-resolution gamma-ray spectroscopy. The highest activity concentrations of all three radionuclides were obtained in the samples that were processed in Japan in 2011 a few months after the Fukushima Daiichi accident. However, the activity concentrations of radiocaesium in all the samples in this study were far below the limit for food and beverages of 100 Bq/kg, which is the standard limit in the Japan.

The concentrations of radiocesium in different organs of wild boar inhabiting Iitate, Fukushima were measured, after the Fukushima Daiichi nuclear power plant accident. After dissection, about 24 parts were collected and measured using a NaI gamma ray counter. In 2012, the radiocesium concentration (134Cs and 137Cs) was highest in muscle (approximately 15,000 Bq kg−1) and low in ovary, bone and thyroid gland, indicating large variation among tissues. Radiocesium concentrations in 24 different organs revealed the pattern of distribution of radiocesium in wild boar and indicated its availability in the ecosystem of the forests and villages where the boars matured.

The dataset “Spatial datasets of radionuclide contamination in the Ukrainian Chernobyl Exclusion Zone” was developed to enable data collected between May 1986 (immediately after Chernobyl) and 2014 by the Ukrainian Institute of Agricultural Radiology (UIAR) after the Chernobyl accident to be made publicly available. The dataset includes results from comprehensive soil sampling across the Chernobyl Exclusion Zone (CEZ). Analyses include radiocaesium (134Cs and 134Cs) 90Sr, 154Eu and soil property data; plutonium isotope activity concentrations in soil (including distribution in the soil profile); analyses of “hot” (or fuel) particles from the CEZ (data from Poland and across Europe are also included); and results of monitoring in the Ivankov district, a region adjacent to the exclusion zone. The purpose of this paper is to describe the available data and methodology used to obtain them. The data will be valuable to those conducting studies within the CEZ in a number of ways, for instance (i) for helping to perform robust exposure estimates to wildlife, (ii) for predicting comparative activity concentrations of different key radionuclides, (iii) for providing a baseline against which future surveys in the CEZ can be compared, (iv) as a source of information on the behaviour of fuel particles (FPs), (v) for performing retrospective dose assessments and (vi) for assessing natural background dose rates in the CEZ. The CEZ has been proposed as a “radioecological observatory” (i.e. a radioactively contaminated site that will provide a focus for long-term, radioecological collaborative international research). Key to the future success of this concept is open access to data for the CEZ. The data presented here are a first step in this process. The data and supporting documentation are freely available from the Environmental Information Data Centre (EIDC) under the terms and conditions of the Open Government Licence: https://doi.org/10.5285/782ec845-2135-4698-8881-b38823e533bf.

Six months after the explosion of TEPCO's Fukushima Dai-ichi nuclear power plant, radioactive silver ((110m)Ag), was detected in concentrations of 3754 Bq/kg in Nephila clavata (the orb-web spider; Joro-gumo in Japanese) collected at Nimaibashi, Iitate village in Fukushima Prefecture, whereas (110m)Ag in the soil was 43.1 Bq/kg. A survey of 35 faunal species in the terrestrial environment during the 3.5 years after the accident showed that most of Anthropoda had two orders higher (110m)Ag in their tissues than soils, although silver is not an essential element for their life. However, tracing of the activity of (110m)Ag detected in spider Atypus karschi collected regularly at a fixed location showed that it declined much faster than the physical half-life. These results suggest that (110m)Ag was at once biologically concentrated by faunal species, especially Arthropoda, through food chain. The factors affecting the subsequent rapid decline of (110m)Ag concentration in faunal species are discussed.

Car-borne surveys were carried out on eight islands of the Izu Islands located 339-570 km southwest of the Fukushima Daiichi Nuclear Power Plant. The mean dose rates measured in 2015, 2016 or 2017 on each island were from 12 to 47 nGy h-1, meaning that the contribution ratios of artificial radionuclides were 5-31%. Based on the environmental half-life for long half-life radionuclides (134Cs + 137Cs) measured on Izu-Oshima (3.1 y), the mean dose rates in March 2011 were estimated to be 15-53 nGy h-1 and the contribution ratios of artificial radionuclides were 11-55%. The estimated annual external effective doses were 0.06-0.21 mSv which were 13-44% of the worldwide average (0.48 mSv).

The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident resulted in a release of radionuclides into the environment. Since the accident, measurements of radiation in the environment such as air dose rate and deposition density of radionuclides have been performed by various organizations and universities. In particular, Japan Atomic Energy Agency (JAEA) has been performing observations of air dose rate using a car-borne survey system continuously over widespread areas. Based on the data measured by JAEA, we estimated effective dose from external exposure in the prefectures surrounding Fukushima. Since car-borne survey started a few months after the accident, the main contribution to measured data comes from 137Cs and 134Cs whose half-lives are relatively long. Using air dose rate of 137Cs and 134Cs and the ratio of deposition density of short-lived nuclides to that of 137Cs and 134Cs, we also estimated contributions to the effective dose from other short-lived nuclides.

Nuclear weapons represent one of the most immediate threats of mass destruction. In the event that a procured or developed nuclear weapon is detonated in a populated metropolitan area, timely and accurate nuclear forensic analysis and fallout modeling would be needed to support attribution efforts and hazard assessments. Here we demonstrate that fissiogenic xenon isotopes retained in radioactive fallout generated by a nuclear explosion provide unique constraints on (1) the timescale of fallout formation, (2) chemical fractionation that occurs when fission products and nuclear fuel are incorporated into fallout, and (3) the speciation of fission products in the fireball. Our data suggest that, in near surface nuclear tests, the presence of a significant quantity of metal in a device assembly, combined with a short time allowed for mixing with the ambient atmosphere (seconds), may prevent complete oxidation of fission products prior to their incorporation into fallout. Xenon isotopes thus provide a window into the chemical composition of the fireball in the seconds that follow a nuclear explosion, thereby improving our understanding of the physical and thermo-chemical conditions under which fallout forms.

To investigate the time variations of radionuclides discharged from the Fukushima Daiichi nuclear power plants accident, we started collecting aerosol samples in Osaka, Japan, using a high-volume sampler from March 15 to May 1, 2011. Atmospheric radioactivity concentrations of I-131, Cs-134 and Cs-137 were measured with germanium semi-conductor detectors. Only I-131 was detected in the early phase and two Cs-134.137 peaks were found in Osaka in April. Using the HYSPLIT model, we concluded that direct transportation of the air mass from the Fukushima area was responsible for such events.

A method of estimating surface radioactivity concentrations of key anthropogenic radionuclides from NaI(Tl) pulse-height distribution observed at a monitoring station (MS) was discussed. In the estimation, a realistic assumption on geometric distribution of source and obstacles around the detector of the MS including the infiltration of radionuclides into the ground was used and the results were compared with ones with a commonly used assumption of a uniformly distributed plane source. The surface radioactivity concentration was determined by comparing the count rates at the full-energy peak ranges between observation and calculation with an electron-photon transport code EGS5. It was shown that the estimated absolute values of concentration differed by a factor of ∼1.5 depending on the assumption of infiltration depth. The estimated surface concentrations of (131)I, (134)Cs and (137)Cs were in good agreement with ones determined by the in situ measurements with an HPGe detector and the cumulative values of daily surface depositions.

Total radioactivity of 137Cs in water samples from the Niida River was 0.025–4.18 Bq/L during May 2011–November 2012. Higher radioactivity was found during May–September 2011 and after a high flow condition caused by a rain event in 2012. The particulate phase of 134Cs and 137Cs was 47–48 % for May–September 2011, 75–93 % in normal flow conditions and 86–91 % in high flow conditions after December 2011. These results indicate that the supply of 134Cs and 137Cs from the watershed differs from the early stage up to September 2011 and from the last stage.

AGR-1 was the first in a series of experiments designed to test US TRISO fuel under high temperature gas-cooled reactor irradiation conditions. This experiment was irradiated in the Advanced Test Reactor (ATR) at Idaho National Laboratory (INL) and is currently undergoing post-irradiation examination (PIE) at INL and Oak Ridge National Laboratory. One component of the AGR-1 PIE is the experimental evaluation of the burnup of the fuel by two separate techniques. Gamma spectrometry was used to non-destructively evaluate the burnup of all 72 of the TRISO fuel compacts that comprised the AGR-1 experiment. Two methods for evaluating burnup by gamma spectrometry were developed, one based on the Cs-137 activity and the other based on the ratio of Cs-134 and Cs-137 activities. Burnup values determined from both methods compared well with the values predicted from simulations. The highest measured burnup was 20.1% FIMA (fissions per initial heavy metal atom) for the direct method and 20.0% FIMA for the ratio method (compared to 19.56% FIMA from simulations). An advantage of the ratio method is that the burnup of the cylindrical fuel compacts can be determined in small (2.5 mm) axial increments and an axial burnup profile can be produced. Destructive chemical analysis by inductively coupled mass spectrometry (ICP-MS) was then performed on selected compacts that were representative of the expected range of fuel burnups in the experiment to compare with the burnup values determined by gamma spectrometry. The compacts analyzed by mass spectrometry had a burnup range of 19.3% FIMA to 10.7% FIMA. The mass spectrometry evaluation of burnup for the four compacts agreed well with the gamma spectrometry burnup evaluations and the expected burnup from simulation. For all four compacts analyzed by mass spectrometry, the maximum range in the three experimentally determined values and the predicted value was 6% or less. The results confirm the accuracy of the nondestructive burnup evaluation from gamma spectrometry for TRISO fuel compacts across a burnup range of approximately 10–20% FIMA and also validate the approach used in the physics simulation of the AGR-1 experiment.

Numerical simulations on oceanic 134 Cs and 137 Cs dispersions were intensively conducted in order to assess an effect of the radioactive cesium on the North Pacific environment with a focus on the long-term variation of the radioactive cesium concentration after the Fukushima disaster that occurred in March 2011. The amounts of 134 Cs and 137 Cs released into the ocean were estimated using oceanic monitoring data, whereas the atmospheric deposition was calculated through atmospheric dispersion simulations. The highly accurate ocean current reanalyzed through a three-dimensional variational data assimilation enabled us to clarify the time series of the 134 Cs and 137 Cs concentrations in the North Pacific. It was suggested that the main radioactive cesium cloud due to the direct oceanic release reached the central part of the North Pacific, crossing 170°W one year after the Fukushima disaster. The radioactive cesium was efficiently diluted by meso-scale eddies in the Kuroshio Extension region and its concentration in the surface, intermediate, and deep layers had already been reduced to the pre-Fukushima background value in the wide area within the North Pacific 2.5 years after the Fukushima disaster.

We measured the concentrations of several radionuclides in atmospheric deposition samples collected in the period from 2000 to 2012 at Rokkasho, Japan. Monthly 7Be deposition rates were higher in winter/spring and fall, and monthly 210Pb deposition rates were highest in winter/spring. Following the accident at the Fukushima Dai-ichi Nuclear Power Plant in March 2011, the radiocesium (134Cs and 137Cs) deposition rate rapidly increased until it reached the maximum in April 2011, after which the deposition rate of 137Cs decreased with a half-time of 22 days before remaining constant throughout 2012.