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The medical situation during disasters often differs from that at usual times. Disasters can lead to significant mortality that can be difficult to monitor. The types of disaster-related deaths are largely unknown. In this study, we conducted a survey to categorize the disaster-related deaths caused by a radiation disaster. A total of 520 people living in Minamisoma City, Fukushima Prefecture, at the time of the Fukushima Daiichi Nuclear Power Plant accident, who were certified to have died due to disaster-related causes were surveyed. We divided the participants into those who were at home at the time of the earthquake and those who were in hospitals or facilities when the disaster struck and conducted a hierarchical cluster analysis of the two groups. Disaster-related deaths could be divided into seven groups for those who were at home at the time of the disaster and five groups for those who were in hospitals or facilities at the time of the disaster. Each group showed different characteristics, such as "the group with disabilities," "the group receiving care," and "the group with depression," and it became evident that not only uniform post-disaster support, but support tailored to the characteristics of each group is necessary. [ABSTRACT FROM AUTHOR]

The United States Nuclear Regulatory Commission issued requests for licensees to re-evaluate the seismic hazards at their sites after the accident at the Fukushima Daiichi Nuclear Power Plant in Japan on March 11 in 2011 and to identify and address any site-specific vulnerabilities associated with seismic hazards. The primary guidance for performing those evaluations is provided in the Electric Power Research Institute EPRI-1025287 report, which also provides guidance for evaluating spent fuel pool (SFP) integrity. In addition, the EPRI-3002009564 report also provides evaluation approaches regarding the effects of seismic ground motions on SFPs that supplement the guidance provided in EPRI-1025287. SFP integrity has become increasingly important for active and decommissioned nuclear power plants. According to EPRI-1025287, the SFP integrity evaluation emphasizes failure modes of the SFP that could result in "rapid drain-down." The definition of "rapid drain-down" is a failure that could lead to the uncovering of irradiated fuel stored in the SFP within 72 h of an earthquake. Possible failures can be classified into two categories: failures relevant to the SFP structure and failures relevant to non-structural elements. This paper aims to study the approaches of implementing seismic evaluation of an SFP structure. EPRI-3002009564 provides separate seismic evaluation approaches for plants with a ground motion response spectrum (GMRS) peak Sa ≤ 0. 8 g and for plants with a GMRS peak Sa > 0. 8 g. Structural dynamic analysis is also a common approach for implementing seismic evaluation if a detailed finite element model is available. In this paper, a sample SFP structure was evaluated using the two approaches, structural dynamic analysis and structural analysis criteria. The results indicate that shear failure controlled the failure mode of the SFP structure for both approaches. This shows that the two approaches drew the same conclusion regarding the failure mode. Furthermore, a smaller seismic margin was obtained using the structural analysis criteria, which means this evaluative approach is more conservative. [ABSTRACT FROM AUTHOR]

Radionuclide contamination in foods has been a public concern in Japan after the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. To estimate time and regional trends of daily intake and annual committed effective dose of strontium-90 (90Sr) after the accident, we analysed Market basket samples using a low background 2π gas-flow counter. Samples were collected from six regions, once a year from 2013 to 2018. There appeared to be little variation in estimated daily intake and annual committed effective dose of 90Sr across the time periods and regions. The estimated maximum annual committed effective dose of 90Sr was 0.00076 mSv/year, a value sufficiently lower than the intervention exemption level, 1 mSv/year, in foods in Japan. There was no noticeable difference between the range of estimated daily intake of 90Sr in this study compared with daily intake measured before the FDNPP accident. These results suggested that no obvious increase in dietary intake of 90Sr was observed after the FDNPP accident, and that the effects on commercial foods from 90Sr due to the FDNPP accident were negligible. [ABSTRACT FROM AUTHOR]

The Fukushima Daiichi Nuclear Power Plant accident, triggered by the Great East Japan Earthquake and the tsunami, has had a major impact on societies across the world. The subsequent focus on decommissioning efforts has attracted worldwide attention. It has been consistently asserted since the aftermath of the accident that the decommissioning of the Fukushima Daiichi Nuclear Power Plant will take approximately 30 to 40 years. The promotion of decommissioning work means that we will continue to face the problems with uncertainties in the work, as sometimes referred to as Unknown Unknowns. Typical elemental technologies required in remotely operated robotic systems for decommissioning include mobile mechanisms and their control, handling mechanisms and their control, information communication, operation interface (information presentation and command input), shielding (radiation resistance) and so on. Although many tasks using remotely operated robotic systems have been carried out with noteworthy results, there are lingering issues yet to be clarified. To ensure the safe and effective execution of various types of decommissioning tasks over a period of several decades, continuous research and development of each elemental technology are imperative, and these technologies must be integrated into a system appropriately to the assumed tasks. In addition, human resource development and the transfer of knowledge and experience are also important issues. From such viewpoint, this special issue is titled "Robotic, Mechatronic and Information Systems for Decommissioning." It contains papers and development reports on robotics, mechatronics, information processing, and information systems technologies relevant to decommissioning work. It also features recent activities of nuclear emergency response organizations. We hope this special issue will acquaint readers with the latest research and development results and organizational activities related to decommissioning. At the same time, we hope that we were able to provide readers interested in robots, mechatronics, and information technology with an opportunity to become aware of the issues and necessary perspectives related to decommissioning and nuclear disasters. Lastly, we would like to thank the editorial board of the Journal of Robotics and Mechatronics, the editorial team of Fuji Technology Press, and the reviewers for their support in the planning and publication of this special issue. Their dedicated efforts are deeply appreciated. [ABSTRACT FROM AUTHOR]

The unexpected accident at the Fukushima Daiichi Nuclear Power Station in Japan, which occurred on March 11th, 2011, after the Great East Japan Earthquake and tsunami struck the north-eastern coast of Japan, released radionuclides into the environment. Today, because of the amounts of radionuclides released and their relatively long half-life, the levels of radiocesium contaminating foodstuffs remain a significant food safety concern. Foodstuffs in Japan have been sampled and monitored for 134,137Cs since the accident. More than 2.5 million samples of foodstuffs have been examined with the results reported monthly during each Japanese fiscal year (FY, from April 1st to March 31st) from 2012 to 2021. A total of 5,695 samples of foodstuffs within the "general foodstuffs" category collected during this whole period and 13 foodstuffs within the "drinking water including soft drinks containing tea as a raw material" category sampled in FY 2012 were found to exceed the Japanese maximum permitted level (JML) set at 100 and 10 Bq/kg, respectively. No samples from the "milk and infant foodstuffs" category exceeded the JML (50 Bq/kg). The annual proportions of foodstuffs exceeding the JML in the "general foodstuffs" category varied between 0.37% and 2.57%, and were highest in FY 2012. The 134,137Cs concentration for more than 99% of the foodstuffs monitored and reported has been low and not exceeding the JML in recent years, except for those foodstuffs that are difficult to cultivate, feed or manage, such as wild mushrooms, plants, animals and fish. The monitoring data for foodstuffs show the current status of food safety risks from 134,137Cs contamination, particularly for cultured and aquaculture foodstuffs on the market in Japan. [ABSTRACT FROM AUTHOR]

A fleet of thirteen in-service global container ships continuously measured the air dose rates over the North Pacific after the Fukushima Daiichi Nuclear Power Station (FDNPS) accident. The results showed that the elevated air dose rates over the Port of Tokyo and the FDNPS emissions are significantly correlated (log(emission fluxes) = 54.98 x (air dose rates) (R = 0.95, P-value<0.01), and they are also significantly correlated with the Tsukuba deposition fluxes (log(deposition fluxes) = 0.47 + 30.98 (air dose rates) (R = 0.91, P-value<0.01). These results demonstrate the direct impact of the FDNPS emissions on the depositions of radionuclides and the air dose rates over the Port of Tokyo. Over the North Pacific, the correlation equations are log(emission fluxes) = -2.72 + 202.36 x (air dose rates over the northwestern Pacific) (R = 0.40, P-value<0.01), and log(emission fluxes) = -0.55 + 80.19 x (air dose rates over the northeastern Pacific) (R = 0.29, P-value = 0.0424). These results indicate that the resuspension of the deposited radionuclides have become a dominant source in the transport of radionuclides across the North Pacific. Model simulations show underestimated air dose rates during the periods of 22-25 March 2011 and 27-30 March 2011 indicating the lack of mechanisms, such as the resuspension of radionuclides, in the model. [ABSTRACT FROM AUTHOR]

This paper's theme "Creative Robot Contest for Decommissioning (hereinafter, this Creative Robot Contest)" may be called a contest that would never have been planned in the absence of the Great East Japan Earthquake on March 11, 2011 and the core meltdown accident at Fukushima Daiichi Nuclear Power Plant of Tokyo Electric Power Company. When it was decided to decommission the nuclear reactors, their decommissioning was immediately put in hand, which, however, met with a high barrier of high radiation doses unconquerable even by the modern science and technologies. In order to advance the stagnating decommissioning work and in hopes of some creative breakthrough ideas from KOSEN students, this Robot Contest, first held in 2016, has been held by KOSEN teams who have shown their willingness to participate in it as a venue useful to address any difficulties they will face in the real world or as teaching material for them to consider social problems. This Robot Contest, sponsored by the Japan Atomic Energy Agency and the Council of Technical Colleges for Human Resource Development for Decommissioning, is planned and managed by the Executive Committee of Creative Robot Contest for Decommissioning (hereinafter, the Executive Committee) with its secretariat at National Institute of Technology, Fukushima College (hereinafter, Fukushima KOSEN) in Fukushima Prefecture where Fukushima Daiichi Nuclear Power Plant is located. In this paper, teachers at Osaka Metropolitan University College of Technology (hereinafter, Osaka Metropolitan University KOSEN) and at Nara National College of Technology, Nara College (hereinafter, Nara KOSEN), whose respective teams have participated in this Robot Contest every year from the first one, and teachers at Fukushima KOSEN who organize and manage the executive committee describe their own views on this Robot Contest based on their viewpoints as KOSEN educators. In the first half, this paper reviews this Robot Contest and outlines the robots of Osaka Metropolitan University KOSEN which participated in it in FY2016 and FY2017 and of Nara KOSEN which did in FY2016. In the latter half, this paper describes the views of the KOSEN teachers who educate engineers in the framework of robot contests from the viewpoints of the teachers who have instructed the teams of Osaka Metropolitan University KOSEN and Nara KOSEN who have participated in this Robot Contest up to the sixth one and who have held this Robot Contest. [ABSTRACT FROM AUTHOR]

Even after 7 years of the nuclear accident that occurred in 2011 at the Fukushima Dai-ichi nuclear power plant (F1NPP), high levels of 137Cs have been detected in ambient aerosols from some polluted areas of Fukushima. Higher levels of radionuclides were often observed in the atmosphere during and after rain events. We presume that biological processes such as fungal activity associated with higher relative humidity may be involved with a possible emission of radioactivity to the atmosphere, which was originally emitted from the F1NPP accident and was deposited over the ground, forest, soil, etc. Here, we report, for the first time, relationships of 137Cs and organic tracers of fungal spores (i.e., arabitol, mannitol and trehalose) in the aerosol samples collected from Fukushima, Japan. Although we found twice-higher concentrations of 137Cs at nighttime than at daytime, fungal spore tracers did not show a consistent trend to 137Cs, that is, organic tracers at nighttime were similar with those at daytime or were even higher in daytime. This study has not clearly demonstrated that fungal spores are the important source of high levels of 137Cs at nighttime. The current unclear relationship is probably associated with the sampling strategy (four consecutive days with a sampling on/off program for day/nighttime samples) taken in this campaign, which may have caused a complicated meteorological situation. [ABSTRACT FROM AUTHOR]

• Anaerobic wet fermentations were conducted for treating genuine radioactive grass. • Alkaline-heat and ultrasonic methodologies were used to pre-treat the grass. • Alkaline-heat-treated grass showed an optimal anaerobic conversion efficiency. • Pre-treatments and wet fermentations barely leached Rad-Cs from grass. • Soil with high cesium affinity mixed with grass limited the Rad-Cs leaching. Persistent concerns regarding environmental hazards arise from the difficulty in disposing of radioactive plant-based wastes originating from the nuclear accident at the Fukushima Daiichi Nuclear Power Plant (FNPP) in Japan in 2011. In this study, three anaerobic digestion (AD) strategies were proposed: Sole anaerobic wet fermentation, and wet fermentations with either alkaline-heat or ultrasonic pre-treatment, which were employed for long-term anaerobic treatment of a genuine radioactive grass stemming from the FNPP accident. The objectives of this work are to investigate the effects of pre-treatments on biomass conversion efficiency and to gain insight into the leaching behavior of radiocaesium (Rad-Cs) within AD processes. Experimental results indicate that by introducing alkaline-heat and ultrasonic pre-treatments to AD systems, the removal efficiencies of total solids (TS) from the raw grass increased by 60.8 % and 42.5 %, respectively, compared to sole wet fermentation. Pre-treatments have been shown to enhance the stability of AD systems, both in terms of enhancing methane production and mitigating pH fluctuations triggered by the accumulation of organic acids. Remarkably, even though the Rad-Cs leaching rate was highest when the AD system was fed with the alkaline-heat pre-treated grass, it remained unsatisfactory at only 5.77 %. We inadvertently isolated a soil-like component from the raw grass, and analyzed both its proportion in the raw grass and the radioactivity intensity. The results indicate that although the soil constituted only 9.51 % TS of the raw grass, it accounted for a significant 81.35 % of the total radioactivity. The soil, which has a pronounced affinity for ionic Cs, being mixed into the raw grass, was identified as the primary factor limiting the leaching efficiency of Rad-Cs throughout both the pre-treatment and wet fermentation phases. [Display omitted] [ABSTRACT FROM AUTHOR]

Following the accident at the Fukushima Dai-ichi Nuclear Power Station, radiocaesium concentrations were specifically elevated in rockfish species compared to other fish species. To clarify the likely reasons, a caesium metabolic rate in the Japanese rockfish Sebastes cheni was derived by an aquarium experiment of live fish collected from the area off Fukushima. Stable caesium and 137Cs concentration in prey organisms, stomach contents and muscle of rockfish were measured and the bioavailable fraction in prey organisms was evaluated. Using derived transfer parameters, 137Cs radioactivity levels in S. cheni and prey organisms were simulated by a model, and verified by the measured radioactivity concentrations of biota in coastal waters south of the Fukushima Dai-ichi Nuclear Power Station. As a result, slow caesium metabolism in S. cheni was confirmed with the biological half-life (Tb 1/2) of 190 d. The determining factor for the initial 137Cs radioactivity levels in S. cheni , was the maximum radioactivity levels in surrounding seawater which was constrained by the sedentary nature of rockfish. Controlling factors of depuration rate of 137Cs levels in S. cheni were slow caesium metabolism, enhanced 137Cs radioactivity level of prey organisms, and survival of older contaminated individuals due to a long life-span. During the study period 2017–2021, 137Cs radioactivity concentrations in seawater decreased close to the level measured before 2010, whereas those in prey organisms and rockfish in southern Fukushima waters were still above the levels that existed before 2010. An additional source for enhancing 137Cs radioactivity in rockfish and biota of the food chain was indicated by the greater 137Cs/133Cs atom ratios in rockfish compared to those in the surrounding seawater, however it was considered to be radiologically insignificant in relation to seafood safety limits. • Very slow radiocaesium excretion confirmed in rockfish. • Depuration in rockfish was delayed by 137Cs transfer from prey. • 137Cs excretion in contaminated old fish completed after 10 years. • 137Cs transfer among rockfish and adjacent ecosystems reached equilibrium after 2019. [ABSTRACT FROM AUTHOR]

The process of an aerosol rainout in wet deposition induces large uncertainties among atmospheric aerosol simulations, especially for particles in the fine mode. In this study, we performed an intercomparison study of four different rainout schemes on the model (the nonhydrostatic icosahedral atmospheric model or NICAM) to simulate particulate Cs-137 in the emission scenario of the March 2011 accident at the Fukushima Dai-ichi Nuclear Power Plant. The schemes include global climate models (GCMs) approach with a simple tuning parameter to determine the scavenging coefficient, and another optimized for cloud resolving models (CRMs) to account for prognostic precipitation and realistic vertical transport. The third approach was the conventional method under the assumption of a pseudo-first-order approximation based on the surface precipitation flux. The fourth approach was involved in offline chemical transport models (CTMs) with a simplified parametric analysis approach to clouds and precipitation flux. In most experiments, statistical metrics of the Cs-137 concentrations using in-situ measurements were calculated to be within ±30 % (bias), 0.6 - 0.9 (correlation), 67 - 112 Bq m-3 (uncertainty), and < 40 % (precision within a factor of 10). The CRM-type method yielded the best results but required a lower limit of tuning parameters to compensate for the results. Both the GCM-type and the conventional methods were also useful by setting proper tuning parameters. The CTM-type yielded better correlation and lower uncertainty but larger negative bias. These analyses suggest the overestimation of the conversion rate from cloud droplets into raindrops by the NICAM. However, this cannot be resolved by simply interchanging cloud microphysics schemes. It was found that the sensitivity of the rainout scheme has a stronger influence on the Cs-137 concentration than the different treatments of cloud microphysics. Thus, to replicate the observed Cs-137 distribution, it is essential to have a better meteorological field as well as a proper rainout scheme. [ABSTRACT FROM AUTHOR]

After the accident at the Fukushima Daiichi Nuclear Power Plant (FDNPP), much of the wild and edible mushrooms and plants in the surrounding areas were contaminated with radiocesium (137Cs). To elucidate their concentration characteristics, we analyzed 137Cs radioactivity data in edible forest products brought in for food inspection by the residents of Kawauchi Village, 12–30 km away from the FDNPP, from 2012 to 2019. A Bayesian model to estimate 137Cs concentration was constructed. Parameters of the normalized concentration of species (NCsp) for mushrooms were similar to those of the same species obtained in a previous study. Although NCsp values were highly varied among species, mycorrhizal mushrooms tended to have high NCsp values, followed by saprotrophic mushrooms, and wild edible plants values were low. Also, half of mycorrhizal mushroom species (8 of 16) showed an increasing trend in concentration with time; however, saprotrophic mushrooms and wild plants generally demonstrated a decreasing trend (22 of 24). The model considering the sub-village location information decreased the error of individual samples by 40% compared to the model not considering any location information, indicating that the detailed geo-information improved estimation accuracy. Our results indicate that the radioactivity data from samples collected by local residents can be used to accurately assess internal exposure to radiation due to self-consumption of contaminated wild mushrooms and plants. [ABSTRACT FROM AUTHOR]

An enormous amount of environmental monitoring data has been acquired by various organisations for the evaluation and implementation of countermeasures to mitigate the effects of the accident at the Fukushima Daiichi Nuclear Power Plant. However, it is difficult to collate, compare, and analyse this data because it was published in different formats at different sites according to the respective objectives of the publishing organisations. Moreover, these organisations have been accumulating data in large volumes for over nine years after the accident. We established procedures to collect this data, convert them into a unified format, classify them according to categories, and make the data accessible on a web-based database system. The database contains environmental monitoring data on air dose rates, ground deposition densities, and concentrations in various environmental samples such as soil, water, and food. This data is being provided not only in numerical format for quantitative analysis but also as distribution maps and time-series graphs for visual understanding. The database system enabled us to spatially and temporally compare large volumes of monitoring data. By using the database functions, characteristics of some representative data in the database was clarified. [ABSTRACT FROM AUTHOR]

Using two horizontal resolutions (3 km and 250 m), this study examined the performance of Eulerian models in simulating dispersion fields at two coastal monitoring stations in the vicinity of a pollutant source (3.2 km and 17.5 km distant) under the situation of the Fukushima 2011 nuclear accident. A 250-m grid simulation was newly conducted for the examination and was able to reproduce the wind and concentration fields in detail over complex terrain. The 3-km grid model could not reproduce the details of the winds and plumes around the Fukushima Daiichi Nuclear Power Plant but occasionally yielded a higher performance with a lower undetected error rate compared with the 250-m grid model due to the large numerical diffusion of the former. A disadvantage of Eulerian dispersion models is expected to be the artificial numerical diffusion in the advection process near emission sources. The artificial numerical diffusion increases the false alarm ratio (number of strikeouts while swinging) but fortunately decreases the undetected error rate (number of strikeouts while looking). This characteristic is appropriate for environmental emergency response (EER) systems. Furthermore, the 250-m grid model result was improved by a plume augmentation (i.e., max pooling) process, which enlarged the plume widths and masked short time lags and small plume drifts. Plume augmentation was advantageous to the high-resolution model for improving statistical scores, which is beneficial for EER systems. [ABSTRACT FROM AUTHOR]

After the triple disaster of 3.11, the region along the coast of Northeast Japan has been continuously transforming. Especially in Fukushima Prefecture, where a series of accidents at the Fukushima Daiichi Nuclear Power Plant resulted in high radioactive contamination, the event's aftermath still lingers on. In this challenging time, local religious communities show a heightened need for religious ritual and socio-communal reconstruction. They experienced the disaster first-hand and had to re-establish their religious sites and recreate their communities, while simultaneously becoming a source for coping strategies and a hope for those in distress. This article provides initial findings of how the triple disaster has impacted religious communities in Fukushima by drawing from the results of fieldwork done among a Shinto and a Baptist community in 2018. Loss and reconstruction become defining parameters for the reconfigurations of communal life upon return. With their re-claimed spaces in the region, the communities try to decisively shape the reviving of the region. [ABSTRACT FROM AUTHOR]

The accident at the Fukushima Daiichi Nuclear Power Station resulted in 170,000 evacuees, and 10 years on their number still exceeds 40,000. The Japanese government set the standards of compensation that it ordered TEPCO to pay evacuees. However, many evacuees are dissatisfied with the compensation amount and by the absence of a government apology, with some 15,000 people filing 28 lawsuits against TEPCO and the government. Based on the statements submitted to the court and on our questionnaires, this paper seeks to establish a "life document" of 171 evacuees from 54 households who filed a complaint with the Kyoto District Court. [ABSTRACT FROM AUTHOR]

It has been almost 10 years since the accident at Tokyo Electric Power Co., Inc.'s Fukushima Daiichi Nuclear Power Plant in March 2011. This study elucidates changes in the mental states of mothers and children residing in low-dose radiation contaminated regions within Fukushima Prefecture over a five-year period after the Fukushima Daiichi accident. From 2011 to 2015, questionnaire surveys assessing psychological symptoms, including posttraumatic stress disorder-related responses, depressive responses, and stress responses, and radiation protection behaviors were conducted with 18,741 mothers of children aged four, 18, and 42 months. Mothers' and children's psychological symptoms and mothers' radiation protection behaviors were highest in 2011, immediately following the nuclear accident, but decreased over time. However, even in 2015, psychological symptoms and radiation protection behaviors were higher for children and mothers within Fukushima Prefecture than for those in a control group living in regions outside the area, which were minimally affected by the accident. The results suggest that the psychological effects in mothers and children living in low-dose radiation contaminated areas continued for at least five years after the accident. Furthermore, psychological effects in children born after the incident were likely to have been triggered by the parental behavior of mothers who were negatively affected by anxiety and stress. This finding raises concerns regarding the accident's long-lasting psychological effects in mothers and children living in low-contamination regions. [ABSTRACT FROM AUTHOR]

The unpredicted nuclear accident by the Fukushima Daiichi Nuclear Power Plant (F1NPP) is a global concern for human health and ecosystems. In the present study, five-year fluctuations and accumulations of Cs, 134Cs and 137Cs in the Japanese eel were examined in Northeast Japan. The eel is one of the most important research subjects in fishery resources in Asia. The total radioactive Cs, 134Cs and 137Cs levels in the fish gradually decreased throughout the five-year study period after the F1NPP accident. A faster decay rate was found for 134Cs (10–15%) for five years after the F1NPP accident, and the decay of 137Cs (30–90%) was slower during the five years. The difference of decay rates between radiocaesiums might be explained by their different half-lives. The F1NPP derived 134Cs contamination might cease unless fresh input may be detected, and 137Cs might still be distributed and remain in the natural environment. [ABSTRACT FROM AUTHOR]

The study determined whether consumers informed about radiation have a higher willingness to buy (WTB) bottled water from regions near the Fukushima Daiichi Nuclear Power Plant (Fukushima Daiichi). The study also investigated what types of radiation knowledge are effective in mitigating negative images about bottled water from these regions. We found that consumers with radiation knowledge have a higher WTB than those uninformed about radiation, and some types of radiation knowledge have a positive effect on WTB. Our study indicates the importance of enhancing radiation knowledge to improve WTB bottled water from regions near the Fukushima Daiichi. [ABSTRACT FROM AUTHOR]

The present study aimed to clarify the psychological status of 766 former residents of Tomioka Town, Fukushima Prefecture, and their intent to return (ITR) 8 years after the disaster at Fukushima Daiichi Nuclear Power Plant. We investigated their ITR home and their perception of the risk of health effects from radiation exposure. We also evaluated rates of post-traumatic stress disorder (PTSD) using a PTSD checklist (PCL-S) and of psychological stress using the patient health questionnaire-9 (PHQ-9). Among the residents, 102 (13%) had returned home (group 1), 214 (28%) were unsure about returning (group 2), and 450 (59%) had decided not to return (group 3). Concern about exposing the next generation to radiation was significantly more prevalent in groups 2 and 3 than in group 1. The frequency of positive PCL-S and PHQ-9 responses was higher in group 2 than in groups 1 and 3. Factors that were independently associated with returning to Tomioka were positive PCL-S (OR, 4.3) and PHQ-9 (OR, 2.2) scores, concerns about consuming locally sourced food, and living with children, and were more prevalent in group 2 than group 1 (reference). Group 2 was more anxious about radiation exposure and health effects, and had higher rates of psychological stress and PTSD. Providing support to such residents through careful risk communication will be required to recover this community after the nuclear disaster. [ABSTRACT FROM AUTHOR]

Since the accident at Fukushima Daiichi Nuclear Power Plant, individual external doses of residents have been investigated. To accurately analyse survey data, a variety of information, including the activity patterns of many residents, needs to be integrated. However, such large-scale surveys have not yet been conducted and actual individual external doses in Fukushima are unclear. In this study, the individual external doses of approximately 300 Tokyo Electric Power Company Holdings employees, who live and work in Fukushima Prefecture outside the Fukushima Daiichi Nuclear Power Plant, were measured. The employees carried GPS loggers and personal dosimeters capable of measuring dose in counts per minute. The employees' individual external doses were compared along with their activity patterns. It was found that the annual additional individual external dose estimated based upon actual measurements was 1 mSv or less, and the influence on the individual external dose was also revealed. [ABSTRACT FROM AUTHOR]

One of biggest public health impacts of the Fukushima Daiichi Nuclear Power Station accident is psychosocial. Anxiety about radiation is still present, and radiation risk perception, particularly with regard to genetic effects, is known to affect mental health. However, roles of other risk factors such as health anxiety and of mindfulness remain to be proved. Here, we examined how radiation risk perception (genetic effects) mediates in health anxiety and psychological distress, and how mindfulness influences those variables. Seven years after the accident, we commissioned a self-reported online survey with 832 participants, 416 each from Fukushima and Tokyo, and modeled the relationship between those variables using Structural Equation Modeling. Health anxiety had a much stronger influence on psychological distress than radiation risk perception. Mindfulness was significantly correlated with both health anxiety and psychological distress, but not with radiation risk perception. The total effects on psychological distress were −0.38 by mindfulness and +0.38 by health anxiety. These results suggest the potential application of mindfulness-based interventions to alleviate health anxiety and psychological distress rather than therapy focused on radiation anxiety. The results underline the effectiveness of community support efforts in Fukushima and highlight the importance of enhancing mindfulness during the chronic phase following a disaster. [ABSTRACT FROM AUTHOR]

Vertical profiles of radiocesium (134Cs and 137Cs) were measured in the western subarctic area of the North Pacific in 2017. The highest concentration of 134Cs, which was derived from the accident of the Fukushima Dai-ichi Nuclear Power Plant in 2011, was 0.14 Bq m−3 (or 1.19 Bq m−3 after the decay correction to the accident date). Although the vertical inventory of 134Cs decreased between 2014 and 2017, the inventory in 2017 was larger than that expected. That was probably arose from the return of some portion of the high-concentration water mass along with the anticlockwise subarctic gyre current. [ABSTRACT FROM AUTHOR]

Reconstruction has progressed steadily since the 2011 TEPCO’s Fukushima Daiichi Nuclear Power Station accident. However, some people still hesitate to eat foods from Fukushima or to travel there, and there are concerns about the health risks of radiation. We investigated the relationships among reconstruction-related behavior, risk perception, types of information, and information sources, in order to consider appropriate measures for providing information and promoting reconstruction-related behavior a number of years after the accident. We conducted an online questionnaire survey (n = 1000) of Tokyo residents. First, a factor analysis was conducted on knowledge associated with radiation. Two factors were extracted; namely, “physical knowledge” and “health/social knowledge.” We conducted structural equation modeling to construct a model of “knowledge,” “radiation risk perception,” and “intention concerning reconstruction-related behavior.” “Intention concerning reconstruction-related behavior” decreased with “radiation risk perception” and increased with “health/social knowledge.” In addition, “health/social knowledge” negatively affected “radiation risk perception;” this effect was not large, but it was significant. Second, respondents were clarified by information sources using a cluster analysis. Clusters that included respondents who got information from public relations materials issued by municipalities and websites of administrative agencies had a higher factor score for “health/social knowledge” than other clusters. The cluster of respondents who did not get any particular knowledge had the lowest factor score, which was significant, and also had a low “perception of reconstruction.” [ABSTRACT FROM AUTHOR]

The behaviour of tellurium radionuclides in the Fukushima Dai-ichi Nuclear Power Plant accident was examined to determine if it is consistent with the current understanding of tellurium chemistry, and whether there is any evidence of tellurium dispersal by species other than aerosols (e.g., vapours). Previous speciation studies, hot-cell experiments, in-reactor experiments and the transport from the Chernobyl reactor accident indicated that tellurium would behave primarily as a particulate species that condensed at high temperature, although the initial chemical species may have transformed to other solid species on cooling and reaction with environmental compounds (e.g., air). The main volatile tellurium species expected would be organic tellurides, which could be produced by radiolytic or biochemical routes, and have reasonable stability under environmental conditions. The behaviour of 137Cs, which behaves exclusively as a particulate species in air at environmental temperatures, was compared with that of tellurium. The behaviour of tellurium was found to be consistent with the current understanding and no evidence of significant tellurium transport by vapour species was found. • Tellurium release and transport data from Fukushima Dai-ichi were reviewed. • Tellurium behaved as particulate species only, with no evidence of vapour transport. • Particulate behaviour is consistent with present experimental understanding of Te. [ABSTRACT FROM AUTHOR]

• The models of single basket with spent fuel assemblies were developed and simulations were performed by employing ANSYS FLUENT (computational fluid dynamic) and RELAP5 (one dimensional) codes. • The model, developed using one-dimensional code, allows to describe coolant mixing and received with its results fits well with computational fluid dynamic code calculations. • The loss of cooling accident in the spent fuel pools of Ignalina NPP was performed using one-dimensional code RELAP5. The interest in the safety of on-site storage of Spent Fuel Assemblies (SFAs) has been increased after the accident on 11 March 2011, in Fukushima Daiichi Nuclear Power Plant. It is important to analyse the behaviour of not only integral effects in spent fuel pools, but also the local effects during heat removal from the SFAs. Usually, for the integral analysis the one-dimensional system computer codes were used. These codes allow to analyse whole pools and cover long time, with a relatively low cost of computational resources. The Computational Fluid Dynamic (CFD) codes could perform very detailed analysis, but this requires large computational resources. The strong side of CFD codes is the possibility to assess local effects which could occur. In the current work the analysis of heat transfer from the SFAs, placed in special baskets was performed using ANSYS FLUENT 17.2 and RELAP5 codes. The models of single basket with SFAs were developed using both codes. The comparison of calculations allowed to evaluate capabilities of both codes. It is shown, that using one-dimensional system thermal hydraulics code developed model allows to describe coolant mixing inside basket sections and received results fits well with CFD code calculation results. Based on gained experience, the loss of cooling accident in the spent fuel pools of Ignalina NPP was analysed using the model, developed by employing RELAP5 (one-dimensional system thermal hydraulics) code. The calculation results were used for safety evaluation of Ignalina NPP facilities. [ABSTRACT FROM AUTHOR]

• A Phenomena Identification and Ranking Table (PIRT) dedicated to spent-fuel-pool-related accidents; • Eighteen unique phenomena identified as having priority research needs; • About half of these phenomena are related to thermal-hydraulics and heat transfer; • The other half comprises fuel-related phenomena such as fuel volatilization, cladding oxidation in mixed steam–air environment and nitrogen-assisted oxide breakaway at moderate temperature. Motivated by the 2011 accident at the Fukushima Daiichi Nuclear Power Station, the Nuclear Energy Agency (NEA) Committee on the Safety of Nuclear Installations (CSNI) of the Organisation for Economic Cooperation and Development (OECD) launched several activities with the aim to support the post-Fukushima accident decision making process. One of these activities, discussed in the present paper, consisted in the production of a Phenomena Identification and Ranking Table (PIRT) in order to systematically highlight Spent-Fuel-Pool (SFP) accident-related phenomena that are of both high importance and high uncertainty, and thus of primary interest for further experimental or modeling activities. For that purpose, an international panel of experts identified and ranked more than a hundred physical phenomena with regard to their safety importance and current level of knowledge. Altogether eighteen unique phenomena were identified as having priority research needs. About half of these phenomena are related to thermal-hydraulics and heat transfer in the SFP, and they are judged to be important to the coolability of the spent fuel in loss-of-cooling and/or loss-of-coolant accidents. The other half comprises fuel-related phenomena such as fuel volatilization, cladding oxidation in mixed steam–air environment and nitrogen-assisted oxide breakaway at moderate temperature, judged as important and poorly modeled in the scope of SFP accidents. The final part of the paper discusses the research programmes performed on Spent Fuel Pool loss-of-cooling and loss-of-coolant accidents since the publication of the PIRT report in 2018 and the remaining R&D needs. [ABSTRACT FROM AUTHOR]

On 11 April 2011, a magnitude 9.0 earthquake occurred about 154 km northeast of the Fukushima Daiichi Nuclear Power Plant (FNPP1; 37.420° N and 141.033° E). Here we present continuous measurements of the atmospheric dose rates after the Fukushima accident over North Pacific atmosphere by a fleet of thirteen in-service global container cargo ships and another at a Tokyo port site from the Taiwanese PGGM (Pacific Greenhouse Gases Measurements) project. The continuous measurements of atmospheric dose rates were collected from a total of 294 cruises with 41,485 measurements during the period March 2011 to 2015. In this work, we identify three key aspects of the impacts of the radioactive materials following the Fukushima accident: The altitude effect, the land surface effect, and the transported effect. We showed measurements of air dose rates over the land surface areas and over the oceanic atmosphere. The striking differences in the air dose rates measured during the 2011–2015 period clearly identify the deposition effects and the effects associated with radioactive materials transported from the FNPP1. Air dose rates measured over the land surface areas were resulted from a combination of the effects from the deposition of radioactive materials on the surface and the radioactive materials contained in the airborne particles. Air dose rates measured over the oceanic atmosphere contains radioactive effects from airborne particles. The data of air dose rates over the North Pacific atmosphere show the eastward transport of radioactivity. Eastward transport of radioactive materials had been observed after 11 Mar 2011. Monitoring data show that the export of radioactive materials to the Pacific atmosphere occurred after March 2011, and in 2012, 2013, 2014, and 2015. The data are available at https://doi.org/10.6084/m9.figshare.9757697. Our data can help to further develop and verify model for the atmospheric dispersion of nuclear materials from the FNPP1 over the land surface areas and over the North Pacific atmosphere. [ABSTRACT FROM AUTHOR]

Following the March 2011 accident at Fukushima Daiichi Nuclear Power Plant, many residents of Fukushima have faced anxieties about the health impacts of radiation exposure. Considering that source of information may influence resident anxiety, this study aimed to elucidate the correlation between the two. In addition, a health literacy query was included to examine a possible relationship between anxiety and health literacy skills. A mail survey was conducted in August 2016 among 2000 residents of Fukushima Prefecture aged 20 to 79 years. Survey items included questions about current health anxieties caused by radiation, trusted sources of information about radiation, and media used to obtain information on radiation. The survey valid response rate was 43.4%. Results of multiple linear regression analysis revealed that anxiety was significantly higher for the groups indicating “trust in citizen groups” and “use of internet sites.” Anxiety was significantly lower for the groups indicating “trust in government ministries,” “trust in local government,” and “use of local broadcast television.” Also anxiety was significantly lower for groups with higher health literacy. It was found that the significant relationship to anxiety varies depending on the sources of trust and media used. There is a possibility that this was caused by the difference between the contents of each information and media reports. In preparation for any future nuclear accident, government may consider action to improve the media literacy of residents. In addition, improving health literacy of both the recipient and the sender of information can improve access to information and thereby safeguard the health and well-being of the public. [ABSTRACT FROM AUTHOR]

As result of the great east Japan earthquake on March 2011 and the damages of the Fukushima Dai-ichi Nuclear Power Plant (FDNPP), huge amount of radionuclides, especially 137Cs, were released to the Japanese Pacific coast. By consequence, several marine species have been contaminated by direct uptake of radionuclides from seawater or through feeding on contaminated preys. In the present study we propose a novel radioecological modelling approach aiming to simulate the radionuclides transfer to pelagic marine species by giving to the organism body-size a key role in the model. We applied the model to estimate the 137Cs content in 14 commercially important species of the North-Western Pacific Ocean after the FDNPP accident. Firstly, we validated the model and evaluated its performance using various observed field data, and we demonstrated the importance of using such modelling approach in radioecological studies. Afterwards, we estimated some radioecological metrics, such as the maximum activity concentration, its corresponding time and the ecological half-life, which are important in assessment of the previous, current and future contamination levels of the studied species. Finally, we estimated the time duration required for each species to reach the pre-accident 137Cs activity concentrations. The results showed that the contamination levels in the planktivorous species have generally reached the preaccident levels since about 5 years after the accident (since 2016). While in the case of the higher trophic level species, although the activity concentrations are much lower than the regulatory limit for radiocesium in seafood in Japan (100 Bq kg-1), these species still require another 6–14 years (2018–2026) to reach the pre-accident levels. [ABSTRACT FROM AUTHOR]

Molten corium is considered to form in a severe accident at the Fukushima Daiichi Nuclear Power Station (FDNPS). Investigation of the primary containment vessel (PCV) inside the FDNPS showed that a significant amount of the molten corium reached the bottom of the pedestal region. The molten corium and concrete likely caused a complex interaction called Molten Corium Concrete Interaction (MCCI). Then, ex-vessel debris was formed after the solidification of the MCCI products and accumulated in the pedestal region. The solidification hysteresis of ex-vessel debris significantly influences its properties. We performed a thermodynamic analysis using the TAF-ID database to infer the solidification path of U–Zr–Al–Ca–Si–O molten corium, which was chosen for a prototypic system of ex-vessel debris. The solidification path for the CaO-rich sim-corium showed the following sequence: (i) melting as a single liquid phase at temperatures higher than 2430 K, (ii) selective solidification of the oxide-rich corium mainly consisted of fuel materials, and (iii) solidification of the remaining materials as a silicate matrix. In contrast, the solidification path for the SiO 2 -rich corium indicated that (i) formation of liquid miscibility gap above 2200 K between U-rich and Zr-rich oxidic melts, (ii) individual precipitation of solid phases in each liquid phase. Identified features of these solidification paths were in good agreement with the experimental data for the solidified sim-corium. [ABSTRACT FROM AUTHOR]

Eight years after the Fukushima nuclear accident, mosses exposed in bags were used to investigate their ability to accumulate radiocaesium and therefore to act as biointerceptors of 134Cs and 137Cs in the evacuated area of the Fukushima territory. Bags were filled with 3 widely studied moss species (Sphagnum palustre , Hypnum cupressiforme , and Hypnum plumaeforme) and exposed for 3, 6 or 9 weeks at 5 former residential sites within the Fukushima area and, for comparison, at three background sites located 700 km away. The radiocaesium activity concentrations found in moss bags were evaluated as function of exposure time, site conditions and moss species. In the Fukushima area, the moss bags accumulated 137Cs at all exposure sites and in all exposure periods, with S. palustre having the highest 137Cs accumulation ability. The 137Cs activity concentrations (from 28 to 4700 Bq kg−1) measured in moss bags increased with the exposure time and were consistent with the decontamination status of each exposure site, highlighting the big potential of moss bags to discriminate among exposure sites. Time dependency of 137Cs activity concentrations measured in mosses allowed the calculation of location-specific and species-specific factors, which can be used to predict radiocaesium accumulation trends in future biomonitoring surveys performed in the same area with the same experimental design. Autoradiography and electron microscopy analyses of the moss surfaces revealed a prevalence of soil-derived particulate form of radiocaesium, suggesting the use of moss bags as warning sensors of resuspended particles potentially harmful for local residents. [Display omitted] • Mosses in bags act as biosensors of radiocaesium in evacuated Fukushima municipalities. • In Fukushima sites moss-bags highlight 137Cs after only 3 weeks of exposure. • Sphagnum palustre shows the highest 137Cs uptake ability. • Radiocaesium occurs on moss surfaces in soil-derived particulate form. • Location (LF) and Species (SF) factors may help to determine 137Cs accumulation trends. [ABSTRACT FROM AUTHOR]

We conducted a review on the application of two-phase thermosyphons in passive residual heat removal systems (PRHRs). Thermal management to handle the heat of decay in nuclear power plants is crucial for maintaining the integrity of the reactor core. Nuclear power plants are equipped with decay heat removal systems under normal and accident conditions. These systems are generally known as residual heat removal systems. The technology of decay heat removal that relies on electric power, known as an active system, will become ineffective when there is a total loss of electrical power for an extended period (e.g., extended station blackout (SBO)), such as the accident at the Fukushima Daiichi Nuclear Power Plant. To deal with SBO accidents, the design of Generation III+ and small- and medium-size nuclear power plants already includes PRHR systems, which is designed to function for at least 72 h without operator intervention. On the other hand, the use of two-phase thermosyphons as part of thermal management in nuclear power plants is also increasing. This review aims to determine the current status and challenges of the PRHR system design and the application of two-phase thermosyphons in PRHR design. The tools and models used for analyzing PRHR designs are also included in this review. Therefore, a review of thermal-hydraulic performance PRHR that uses the two-phase thermosyphon has been prepared based on simulation and experimental approaches found in the literature. This review focuses on the design and analysis of PRHR systems for light water reactors (LWR) and the usage of two-phase thermosyphon as cooling devices for nuclear-spent pools and non-transient cooling for both LWR and non-LWR reactors. We highlight the PRHR system design and the application of two-phase thermosyphons in PRHR design. As major contributions, different configurations of long-term cooling of PRHRs are discussed. It has been found that to extend the working life of PRHR beyond 72 h, several researchers have proposed new designs with unlimited cooling capabilities. One of the proposed technologies to support PRHR systems of this type is the sub-atmospheric two-phase thermosyphon. It has also found that RELAP5 is the most frequently used PRHR system design analysis tool. This paper, as a whole, acts as a current reference for researchers and lays the groundwork for future research in the use of two-phase thermosyphon for long-term decay heat removal systems. • Passive residual hear removal systems (PRHRs) are to increase the safety of nuclear power plants (NPPs). • Currently, PRHRs are generally designed to function passively for 3 days. • Heat Pipes and two-phase thermosypons are studied as passive cooling in the NPPs. • Two-phase thermosyphons are capable to extend the PRHR's operation for indefinite. • Thermal hydraulic system codes are widely used for PRHR performance analysis. [ABSTRACT FROM AUTHOR]

We measured dissolved radiocesium (134Cs and 137Cs) in surface seawater collected in the western subarctic area of the North Pacific Ocean, Bering Sea, and Arctic Ocean in 2019 and 2020. The radiocesium released from the accident of the Fukushima Dai-ichi nuclear power plant (FNPP1) in 2011 was still observed in these areas (∼2 Bq m−3 decay-corrected to the date of the accident). In 2019/2020, the FNPP1-derived radiocesium concentrations in the Bering Sea and the Chukchi Sea, which is a marginal sea of the Arctic Ocean connecting the Bering Sea to the Arctic Ocean, were within the range of those observed in 2017/2018. On the other hand, the FNPP1-derived radiocesium was detected in the Arctic Ocean farther north of the Chukchi Sea in 2019/2020 for the first time. This was probably derived from the long-range transport of the FNPP1-derived radiocesium from the North Pacific coastal area of Japan to the Arctic Ocean through the Bering Sea during the past decade. The transport of the FNPP1-derived radiocesium from the Bering Sea to the western subarctic area in 2019/2020 is not clear, which implies the retainment of the FNPP1-derived radiocesium within the Bering Sea. • Radiocesium was measured in the North Pacific, Bering, and Arctic in 2019/2020. • FNPP1-derived radiocesium had been transported to the Bering Sea by 2017. • FNPP1-derived radiocesium had arrived in the Arctic Ocean north of 71°N by 2019. • FNPP1-derived radiocesium has been possibly retained within the Bering Sea. [ABSTRACT FROM AUTHOR]

• A simulation and machine learning informed model (SMLIM) is proposed. • An LSTM network model is developed for forecasting and regression analysis. • The model has four feature variables with dry-well pressure as the target variable. • The accident at the Fukushima Daiichi Nuclear Power Plant (FDNPP) unit 1 is chosen. • Training and test data are generated by MELCOR simulations. • Measured data at the FDNPP is analyzed with SMLIM. • SMLIM is shown to be useful for the diagnosis of the accident. We propose a simulation and machine learning informed model (SMLIM) for the diagnosis of severe accidents. A machine learning model which consisted of one hidden Long Short Term Memory (LSTM) layer and two dense layers with variations in the number of neurons and regularization parameters and an Adams optimizer was constructed for the multi-time step ahead forecasting analysis and the regression analysis. Using feature variables of lower plenum liquid level, core liquid level, reactor vessel pressure, and dry-well pressure, which were monitored during the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, the target variable of the dry-well pressure in time was predicted. Training data representing the reference scenario was produced by a MELCOR simulation of the FDNPP accident at unit 1. The first test set obtained from the MELCOR simulation was chosen to consider the aleatoric uncertainty, while the second test set from the MELCOR simulation addresses the epistemic uncertainty. It is shown that the proposed SMLIM model can forecast the time series data with reasonable accuracy for the test cases selected. Then another test sets were prepared using the measurement data taken from the FDNPP. While the forecasted prediction was quite different from the actual measurement data, which were corrupted, the LSTM network model showed better agreement between the prediction and actual data when the measurement data were corrected. This trend was similar in the case of regression analysis. We suggest that the proposed simulation and machine learning informed model can help the operator forecast the future trend of accident progression and diagnose corrupted measurement signals. [ABSTRACT FROM AUTHOR]

The Fukushima Dai-ichi Nuclear Power Plant Accident (FDNPPA) derived 134Cs, 137Cs and 110mAg in blue sharks captured in the Northwest Pacific during 2011–2018 were assessed for the first time in the aspects of radioactive contamination, temporal variation, maternal-to-fetus transfer, tissue distribution and radiation dose, to demonstrate the impacts of the FDNPPA on blue sharks. The contribution of the FDNPPA derived radiocesium in blue sharks (>52%) was estimated based on 134Cs/137Cs activity ratios. The effective and ecological half-lives of the FDNPPA derived 134Cs (270 d, 410 d), and 137Cs (430 d, 450 d) were calculated. These contaminations decreased with time and returned to the level before the FDNPPA during the period of Sep. 2017–Sep. 2018.134Cs and 137Cs tended to distribute in muscles, while 110mAg mainly distribute in their guts. 134Cs and 137Cs were also transferred to fetuses and the activities were up to ~30% of the maternal activities. Dose assessment demonstrated that the highest FDNPPA derived dose rate in blue sharks (~0.42 nGy/h) was far below the ERICA ecosystem screening benchmark of 10 μGy/h and the committed effective dose in humans from ingesting blue shark meat (0.06–0.90 μSv) was far less than that from annual consumption of food and water. It was far from causing radiation harm to blue sharks and humans, suggesting that the impacts of the FDNPPA on blue sharks were not significant. • Impact of Fukushima Nuclear Accident (FNA) on blue sharks were assessed for the first time. • Temporal evolution of FNA derived 137Cs, 134Cs and 110mAg in blue sharks were reported. • Maternal-to-fetus transfer of FNA derived Cs isotopes in blue sharks were studied. • Radiation impacts of FNA on the open ocean ecosystem were not significant. [ABSTRACT FROM AUTHOR]

[Display omitted] • Wildlife remained in areas evacuated by humans after the Fukushima nuclear accident. • Wild boar and snakes were studied in Japan's most radioactively contaminated areas. • Biomarkers of DNA damage (dicentrics) and stress (telomeres, cortisol) were studied. • Comprehensive dosimetry was conducted for chronically exposed free-ranging animals. • No harmful effects were detected from the low dose, low dose rate exposures. The health effects associated with chronic low-dose, low-dose rate (LD-LDR) exposures to environmental radiation are uncertain. All dose-effect studies conducted outside controlled laboratory conditions are challenged by inherent complexities of ecological systems and difficulties quantifying dose to free-ranging organisms in natural environments. Consequently, the effects of chronic LD-LDR radiation exposures on wildlife health remain poorly understood and much debated. Here, samples from wild boar (Sus scrofa leucomystax) and rat snakes (Elaphe spp.) were collected between 2016 and 2018 across a gradient of radiation exposures in Fukushima, Japan. In vivo biomarkers of DNA damage and stress were evaluated as a function of multiple measurements of radiation dose. Specifically, we assessed frequencies of dicentric chromosomes (Telomere-Centromere Fluorescence in situ Hybridization: TC-FISH), telomere length (Telo-FISH, qPCR), and cortisol hormone levels (Enzyme Immunoassay: EIA) in wild boar, and telomere length (qPCR) in snakes. These biological parameters were then correlated to robust calculations of radiation dose rate at the time of capture and plausible upper bound lifetime dose, both of which incorporated internal and external dose. No significant relationships were observed between dicentric chromosome frequencies or telomere length and dose rate at capture or lifetime dose (p value range: 0.20–0.97). Radiation exposure significantly associated only with cortisol, where lower concentrations were associated with higher dose rates (r2 = 0.58; p < 0.0001), a relationship that was likely due to other (unmeasured) factors. Our results suggest that wild boar and snakes chronically exposed to LD-LDR radiation sufficient to prohibit human occupancy were not experiencing significant adverse health effects as assessed by biomarkers of DNA damage and stress. [ABSTRACT FROM AUTHOR]

We conducted single-model initial-perturbed ensemble simulations to quantify uncertainty in aerosol dispersion modeling, focusing on a point-source radioactive aerosol emitted from the Fukushima Daiichi Nuclear Power Plant (FDNPP) in March 2011. The ensembles of the meteorological variables were prepared using a data assimilation system that consisted of a non-hydrostatic weather-forecast model with a 3-km horizontal resolution and a four-dimensional local ensemble transform Kalman filter (4D-LETKF) with 20 ensemble members. The emission of radioactive aerosol was not perturbed. The weather and aerosol simulations were validated with in-situ measurements at Hitachi and Tokai, respectively, approximately 100 km south of the FDNPP. The ensemble simulations provided probabilistic information and multiple case scenarios for the radioactive aerosol plumes. Some of the ensemble members successfully reproduced the arrival time and intensity of the radioactive aerosol plumes, even when the deterministic simulation failed to reproduce them. We found that a small ensemble spread of wind speed produced large uncertainties in aerosol concentrations. [ABSTRACT FROM AUTHOR]

Nuclear power remains one of the most accessible choices in addressing environmental and social concerns due to the continuously increasing energy needs around the world. While it remains an excellent source of energy due to its low price and low level of emissions, potential accidents remain a serious problem. An example of such is the most recent accident in the Fukushima Daiichi Nuclear Power Plant (2011), which reminded the world of the potential risks of nuclear energy and the consequences of which continue to have a lasting effect. There is no nuclear power plant in Serbia, but there are about 15 nuclear power stations scattered within its neighboring countries. Therefore, the Serbian Government decided to study how the Serbian public perceives the risks related to the potential construction of nuclear power stations in the country, nuclear energy in general, and its possible benefits and risks. The objective of this paper is to present the results of this assessment along with a literature overview on the (environmental) risk of nuclear power. A pilot study consisted of a series of 270 randomized face-to-face interviews that took place in the public square of Belgrade in March 2019. Logistic regression was used to examine the cumulative effects of the different risk factors. The results showed that the majority of the respondents are skeptical and do not support the construction of nuclear power stations in Serbia. Furthermore, this research identified several additional important correlations that have a significant impact on the public perception of risk. [ABSTRACT FROM AUTHOR]

• Sensitivity analysis of core slumping and debris quenching in Fukushima NPP Unit-3 have been performed with MELCOR. • Important parameters have been identified for simulating core slumping with MELCOR. • The possible range of debris energy change and coolant inventory loss during core slumping have been estimated. The Great East Japan earthquake and the subsequent tsunami which occurred on March 11th, 2011 put the operating Units 1–3 at Fukushima Daiichi Nuclear Power Plant (NPP) in severe accident conditions and core meltdown due to station blackout. Although research efforts have been made by various parties to study the accident scenarios since the Fukushima accident, there remain unresolved issues regarding the core degradation behavior suggested by measurement data such as water level, Reactor Pressure Vessel (RPV) pressure and Primary Containment Vessel (PCV) pressure. To analyze and resolve such issues would be helpful to promote further understanding of the severe accident scenario at Fukushima units as well as the decommissioning work undergoing. The current study focuses on a detailed analysis of the RPV pressure peak event that occurred in Unit-3 at 12:00 on March 13th 2011. Sensitivity analysis cases were carried out with MELCOR 2.2 code i The MELCOR code version applied in the current study is MELCOR 2.2.9541. The results used in this study were obtained before April 2018 under research collaboration with Waseda University. i with sensitivity parameters that can influence the RPV pressure behavior, such as the debris quenching heat transfer coefficient, the number of opening SRVs during the RPV pressure peak event, amount of core slumping and particulate debris diameter. The cases that could reproduce the RPV pressure peak were further discussed to show likely debris bed energy history and the water mass history in the lower plenum during the RPV pressure peak event. The current study suggests that 1) Opening of SRVs equivalent to the total area of 4–6 fully-open SRVs (or equivalent leak area) could have occurred during the pressurization phase of the RPV accompanied by heavy debris quenching effect, while the opening of SRVs equivalent to a total area of at least 2 fully-open SRVs (or equivalent leak area) could have occurred during the depressurization phase of the RPV accompanied by moderate debris quenching effect. 2) The particulate debris diameter is not a very sensitive parameter when evaluating the debris quenching effect of Unit-3 in the current MELCOR modeling. 3) The current modeling suggests that around 70–110 GJ of energy can be removed by coolant during the debris quenching period with 30 tons of water reduction from the lower plenum. [ABSTRACT FROM AUTHOR]

Much is still not known about the end-state of core materials in each of the units at Fukushima Daiichi Nuclear Power Station (Daiichi) that were operating on March 11, 2011. The Nuclear Energy Agency of the Organization for Economic Development has launched the Preparatory Study on Analysis of Fuel Debris (PreADES) project as a first step to reduce some of these uncertainties. As part of the PreADES Task 1, relevant information was reviewed to confirm the accuracy of graphical depictions of the debris endstates at the damaged Daiichi units, which provides a basis for suggesting future debris examinations. Two activities have been completed within the PreADES Task 1. First, relevant knowledge from severe accidents at the Three Mile Island Unit 2 and the Chernobyl Nuclear Power Plant Unit 4 was reviewed, along with results from prototypic tests and hot cell examinations, to glean insights that may inform future decommissioning activities at Daiichi. Second, the current debris endstate diagrams for the damaged reactors at Daiichi were reviewed to confirm that they incorporate relevant knowledge from plant observations and from severe accident code analyses of the BSAF (Benchmark Study of the Accident at the Fukushima Daiichi Nuclear Power Station) 1 and 2 projects. This paper highlights Task 1 insights, which have the potential to not only inform future Decontamination and Decommissioning activities at Daiichi but also provide important perspectives for severe accident analyses and management, particularly regarding the long-term management of a damaged nuclear site following a severe accident. [ABSTRACT FROM AUTHOR]

• OECD/NEA project "Benchmark Study of the Accident at the Fukushima Daiichi Nuclear Power Plant (BSAF), phase 2. • Severe accident analyses for Unit 2 of Fukushima Daiichi. • Fukushima Daiichi Unit 2 specific aspects will be highlighted, Unit 1 and 3 aspects are presented separately. • Special focus is on reactor pressure vessel status, melt release and fission product behavior and release. This is the second paper in a series of 3 in which results of severe accident analyses for Unit 2 of Fukushima Daiichi are presented, gained in phase 2 of the OECD/NEA project "Benchmark Study of the Accident at the Fukushima Daiichi Nuclear Power Plant (BSAF)". Nine organizations of six countries (CNL Canada; CRIEPI, IAE, JAEA and NRA Japan; IRSN France; KAERI Korea; NRC/DOE/SNL U.S. and VTT Finland) submitted results of their calculated severe accident scenarios for Unit 2 of Fukushima Daiichi using different severe accident codes (ASTEC, MAAP, MELCOR, SAMPSON, THALES-KICHE). The present paper describes the findings of the comparison of the participants' results for Unit 2 against each other and against plant data, the evaluation of the accident progression and the final status inside the reactors. Special focus is on reactor pressure vessel status, melt release and fission product behavior and release. Unit 2 specific aspects will be highlighted and points of consensus as well as remaining uncertainties and data needs will be summarized. [ABSTRACT FROM AUTHOR]

Radioactive caesium was released during the accident of Fukushima Dai-ichi nuclear power plant (FDNPP) into the surrounding environment. In the current work, radiocaesium micro-particles (CsMPs) and radiocaesium-rich soil particles were selectively separated from soil particles as well as from each other using autoradiography-based procedure. The applied separation scheme is based on water dilution followed by drying of the soil sample prior to imaging plate autoradiography. The SEM/EDS investigation of the individual CsMPs showed that these particles have a silicate glass structure and vary in shape with a diameter less than 10 μm. For the first time, a two-stage formation mechanism was suggested for a CsMP based on shape and structure heterogeneity of its two parts. Perfect spherical core might be formed in the first stage with a remarkable lower content of Al, and relatively higher concentrations of Si and K than an outer angulated structure, which might be attached to the core sphere during a late stage. The radiocaesium-rich soil particles have bigger size than CsMPs and have a plate-like structure with cleavages inside the grains, which suggest that these particles might be a weathered biotite. The average radioactivity ratio of 134Cs/137Cs (dated March 11, 2011) in the investigated particles was found to be 1.05 ± 0.01, which confirmed that the radiocaesium in CsMPs and in the contaminated soil particles has the same source of origin, which could be unite 3 of FDNPP. • Caesium micro-particles with glass-like structure released from Fukushima-Daiichi nuclear power plant. • Distinct regions were noticed for the first time inside CsMPs. • Multi-stage formation mechanism was suggested for CsMPs. • Measurement of activity ratio of caesium isotopes. • The source of caesium in soil particles and CsMPs was suggested as unite 3 of FDNPP. [ABSTRACT FROM AUTHOR]

In the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, a considerable amount of radioactive materials were released into the environment. Long-term monitoring is essential for radiation protection and decontamination of the environment. In this study, we analyze the ratio of the air dose rate to 137Cs activity per unit area on the ground over different land use types, and further examine the factors that influence this ratio. It was found that the ratio was relatively higher for forest areas than that for open areas, which may have been caused by effect of continuous 137Cs influx from the forest canopy for a while after the accident. The less influence of vertical migration to the ratio was shown, maybe because the soil shielding effect is negligible by considering more than 75% of 137Cs is still in the surface soil. The ratio is expected to be relatively less changeable in the future, owing to the immobilization of 137Cs in the soil after seven years. The ratio data can be used to estimate future air dose rates, based on the 137Cs activity per unit area for long-term monitoring and evaluation of decontamination activities. • Air dose rate to 137Cs activity per unit area ratio was evaluated. • The ratio was higher in forests than in open areas. • Effect of 137Cs from forest canopy, 137Cs vertical migration in soil and lapsed time was observed. • Less changeable ratio for future dose assessment from 137Cs was predicted. [ABSTRACT FROM AUTHOR]

The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, which occurred in March 2011, has released large amounts of radionuclides (such as radioiodine and radiocesium) into the atmosphere, resulting in the contamination of terrestrial and marine environments. To assess radiological and environmental effects of the FDNPP-derived radionuclides, huge amounts of radioactive monitoring activities have been conducted to environmental samples. In this paper, we review results of atmospheric radioactivity monitoring for the FDNPP accident. Learning from atmospheric radioactivity monitoring of the FDNPP accident is as follows; 1. At the initial stage of accident, large spatiotemporal variability of emitted radionuclides near the FDNPP site occurred at short (less than 1 h) time scale and small (less than 10 km) space scale due to complicated emissions of radionuclides and variable flow of Fukushima radioactive plume, 2. Chemical form of FDNPP-derived radionuclides, in which a typical example is coexistence of 137Cs-bearing submicron particles and 137Cs-bearing large hot particles in the plume, is important to have better understanding of their atmospheric behaviors as do released mechanisms and their fate in environment, 3. Atmospheric effects of the FDNPP accident continue over 8 years, in which high activity levels of the FDNPP-derived 137Cs in surface air and deposition have continued at least until the end of 2018 owing to the post-accident release and resuspension because most of the FDNPP-derived 137Cs deposited on the ground surface still remains in the soil surface as a potential source of atmospheric 137Cs. • The atmospheric effects of radiocesium derived from the Fukushima Daiichi Nuclear Power Plant accident was reviewed. • The maximum activity of 137Cs in surface air near the FDNPP was 13.6 kBq m−3 just after vent operation of Reactor Unit 1. • High radioactive particles with enriched radiocesium were released in the environment. • The late atmospheric effects of the FDNPP-derived radiocesium continued in the end of 2018. • The annual 137Cs deposition showed a small peak in 2017. [ABSTRACT FROM AUTHOR]

• Fractional Release Rates of two samples (in-vessel and ex-vessel) were obtained. • Fraction of Inventory in Aqueous Phase of Mo, Ba, Sr, Rh, La, etc. was obtained. • Geochemical modeling was performed to better understand experimental results. On 11 March 2011, the Great East Japan Earthquake occurred and caused a severe nuclear accident at the Fukushima Daiichi Nuclear Power Station (1F). A policy for corium debris retrieval will be decided in the near future. To this end, debris management after removal from reactors must be optimized. From the viewpoint of cost and waiting for definitive solutions, interim or long-term underwater storage is one of the considered options after debris removal. Leaching data on the long term behavior of debris in water are therefore needed before debris removal. In addition, it is important to understand potential differences in leaching behaviors between debris and Spent Fuel (SF) to get comparative elements. For these reasons, simulated in-vessel and ex-vessel corium debris, fabricated in the Colima experimental facility set up in the PLINIUS platform at CEA Cadarache, were selected and leaching experiments were carried out under oxidizing conditions. In parallel, geochemical modeling was performed to better understand the experimental concentrations, pH evolutions and secondary phase's formation. Finally, the Fractional Release Rates of the (U, Zr)O 2 matrix for the two kinds of samples (in-vessel and ex-vessel) were found to be close to or one order of magnitude lower than that of SF under oxidizing conditions (from 10−6 to 10−7 per day) but the release processes are different. Indeed, the Fraction of Inventory in Aqueous Phase of Mo, Ba, Sr, Rh, La, Nd, Ce and Y tended to be higher than that of uranium and zirconium in this study whatever the element considered. The release of simulating PFs, including low volatile element like trivalent rare earths, does not appear to be fully controlled by that of the (U, Zr)O 2 matrix from a macroscopic and average point of view. The FPs could be partially located outside the (U, Zr)O 2 solid solution as a function of the corium history (quenching rate and thermal history, chemical interactions...). The location of inventories and their chemical forms are not very well known moreover uncertainties related to heterogeneity are important and may also impact the calculation of the global released fractions over time. For the ex-vessel sample, releases into the solution of the main concrete elements (Si, Ca, Mg) seem well correlated and dissociated from the behavior of the (U, Zr)O 2 phase. Further studies are needed especially on real or prototypical corium approaching the conditions of the Fukushima accident. The study of simpler and model systems could also provide information on the reactivity of the (U, Zr)O 2 matrix. [ABSTRACT FROM AUTHOR]

• This paper introduces accident behavior of typical DBAs and BDBAs of the HTR-PM. • All accidents of the HTR-PM have be divided into several categories, each with similar phenomena or same mitigation measures. • The Extended Emergency Operational Procedures (EEOP) and Beyond design basis accident Additional Mitigation Guideline (BAMG) have been developed for the HTR-PM operators. • This work can provide preliminary reference for the further study on the safety regulation, standards or guidelines for design, operation and accident management of the HTGR. High Temperature Gas-cooled Reactor (HTGR), which plays an important role in the worldwide development of Generation-IV nuclear energy technology, is well-known for the high safety, high efficiency and process heat application. A commercial-scale 200 MWe High Temperature gas-cooled Reactor Pebble-bed Module (HTR-PM) has been designed and is now under construction in Shandong Province, China. Most of the construction and installation work have been finished and the connection to the electric grid will be expected in the end of 2020. In this paper, the reactor behaviors of the HTR-PM during the typical design basis accidents (DBAs) and beyond design basis accidents (BDBAs) have been introduced. In the DBAs, the maximum fuel temperature will never exceed its design limitation of 1620 °C, below which under the design burn-up the "Tristructural-isotropic" (TRISO) coated particles can effectively retain their fission-product inventory. Even in the typical BDBAs with extremely low probability, there is enough time, e.g. several days, to adopt appropriate measures to mitigate the consequence, so that the large release of the radioactive materials would not happen. Accident management is important for the nuclear power plant. Besides, After the Fukushima Dai-ichi nuclear accident, in the worldwide, people are more concerned about the severe accident management of the nuclear power plant, and some standards and guidelines are issued. Based on the accident analyses of the HTR-PM, its accident management is studied and discussed. The designers believe that the accident management procedures can be simplified and no offsite emergency measures are needed for the HTR-PM due to the inherent safety design. Compared to the other types of the nuclear power plant, e.g. the Pressurized-Water Reactor (PWR) power plant, the Severe Accident Management Guideline (SAMG) can be simplified or even unnecessary for the HTR-PM. Above work also can provide reference for the further study on the safety regulations, standards or guidelines for the design, operation and accident management of the HTGR. [ABSTRACT FROM AUTHOR]

A series of accidents at the Fukushima Dai-ichi Nuclear Power Plant (1F NPP) following the Great East Japan Earthquake and tsunami of 11 March 2011 resulted in the release of radioactive materials to the ocean. We used the Regional Ocean Model System (ROMS) to simulate the 137Cs activity in the oceanic area off Fukushima, with the sources of radioactivity being direct release, atmospheric deposition, river discharge, and inflow across the domain boundary. The direct release rate of 137Cs after the accident until the end of 2016 was estimated by comparing simulated results with measured 137Cs activities adjacent to the 1F NPP. River discharge rates of 137Cs were estimated by multiplying simulated river flow rates by the dissolved 137Cs activities, which were estimated by an empirical function. Inflow of 137Cs across the domain boundary was set according to the results of a North Pacific Ocean model. Because the spatiotemporal variability of 137Cs activity was large, the simulated results were compared with the annual averaged observed 137Cs activity distribution. Normalized annual averaged 137Cs activity distributions in the regional ocean were similar for each year from 2013 to 2016. This result suggests that the annual averaged distribution is predictable. Simulated 137Cs activity attributable to direct release was in good agreement with measurement data from the coastal zone adjacent to the 1F NPP. Comparison of the simulated results with measured activity in the offshore area indicated that the simulation slightly underestimated the activity attributable to inflow across the domain boundary. This result suggests that recirculation of subducted 137Cs to the surface layer was underestimated by the North Pacific model. During the study period, the effect of river discharge on oceanic 137Cs activity was small compared to the effect of directly released 137Cs. • The direct release rate of dissolved 137Cs was estimated by the end of 2016. • The river discharge rate of dissolved 137Cs was estimated from 2013 to 2016. • The annual averaged 137Cs activity distribution patterns were similar in each year from 2013 to 2016. • Simulated 137Cs activities attributable to direct release were in good agreement with measured activities. • The effect of river discharge of 137Cs was not detected on oceanic 137Cs distributions. [ABSTRACT FROM AUTHOR]

Radiocesium was released to the North Pacific coastal waters by the accident at the Fukushima Dai-ichi Nuclear Power Plant (1FNPP) of the Tokyo Electric Power Company (TEPCO) in March 2011. Since the radiocesium in the sediment off Fukushima was suggested as a possible source for the transfer of this radionuclide through the benthic food chain, we conducted numerical simulations of 137Cs in sediments off the Fukushima coast by using a model which incorporates dynamic transfer processes between seawater and the labile and refractory fractions in sediment particles. This model reproduced the measured temporal changes of 137Cs concentration in seabed surface sediment off Fukusima coasts, by normalizing the radiocsium transfer between seawater and sediment according to the particle diameter sizes. We found that the 137Cs level in sediment decreased by desorption during the first several months after the accident, followed by a reduction in the labile fraction until the end of 2012. The apparent decrease of the total radiocesium level in surface sediment was estimated to occur at rates of approximately 0.2 y−1 within a 20 km distance from the 1FNPP. The comparison of 137Cs level decreases in the demersal fish and the simulated temporal labile fraction in fine sediment demonstrated that the consideration of radiocesium transfer via sediment is important for determining the 137Cs depuration mechanism in some demersal fish. • Numerical simulation was applied to 137Cs transfer in sediments off Fukushima. • The 137Cs in sediment was desorbed during several months after the accident. • Refractory 137Cs fraction in sediment was evaluated as being dominant after 2012. • The apparent 137Cs removal rate from sediment was c.a. 0.2 y−1 during 2013–2018. • Contribution of labile 137Cs fraction for depuration in demersal fish was suggested. [ABSTRACT FROM AUTHOR]