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Before the Fukushima disaster unfolded in 2011, Japanese government and energy company officials were aware of the warning signs and risks of a potential crisis at the reactor site. They failed to use safety mechanisms or update regulations over time to address the vulnerabilities of the power plants. Because interest groups had led the public to believe the power plants were completely safe, the plants were run with little accountability. Following this disaster, Japan established a new nuclear regulatory commission and nuclear regulatory authority in and implemented new regulatory mechanisms. These efforts have been limited, however, and have shifted the issue from regulation to implementation. The enormous cost of meeting new safety protocols has created new barriers for restarting the power plants under updated regulations, but the energy demands of the country will remain. The tension between managing operational risks and meeting public energy needs will test the public and private sectors' ability to sufficiently revamp the nuclear industry and prevent crises in years to come. [ABSTRACT FROM AUTHOR]

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 nuclear‐contaminated water in the seawater near the site of the Fukushima nuclear power plant (NPP) accident is being investigated for treating the radioactive material. One of the most important considerations in the treatment is the management of the vast aquatic area of the oceanic scale. There are two methods in the application of osmosis and filtration for the modeling. There is the molecule quantity by the water volume where the list of transition of quantities is shown, where it decreases to 10% from the reversed osmosis method and to 0.01% from the filtration method in 9 days. In the filtrations, the discharge variations in the sea are described as the maximum and minimum values within 100 square velocities. A design for the general radioactive contaminated seawater treatment facility is introduced. [ABSTRACT FROM AUTHOR]

There has been considerable debate about the formation mechanisms of Cs-bearing silicate glass microparticles (CsMPs) (Types A–E) released uniquely during the Fukushima Daiichi nuclear power station accident. The author proposed that these CsMPs were formed because the high-efficiency particulate air (HEPA) filters or the insulation materials in the reactor building melted and atomized during the hydrogen explosion. However, this hypothesis is complex because it includes the interdisciplinary issues between the thermohydraulics in the reactor and atmospheric dispersion. This paper describes the basis of the hypothesis, verification, future issues, and recommendations from the viewpoint of improving nuclear safety. [ABSTRACT FROM AUTHOR]

More than a decade has passed since the Fukushima nuclear accident in 2011 and contamination around the nuclear power plant is primarily caused by 137Cs. One of the materials retaining radiocesium in the environment is radiocesium-bearing silicate glass microparticles (CsMPs), which have not been reported in previous nuclear accidents. Although the prediction of environmental fates of CsMPs is of interest because of their extremely high specific radioactivity, knowledge about their physicochemical properties is still limited. Here we show that the dissolution behavior of CsMPs is comparable to that of silica-rich glass and significantly depends on the surrounding environment. CsMP dissolution experiments were conducted in solutions with various solute components and pH levels at 60 °C. In neutral and basic solutions, the estimated dissolution rate was accelerated by alkali ions such as Na+, which is known to play a catalytic role for the dissolution of silica. In contrast, the dissolution in acid was slow even in the presence of alkali ions. The dissolution under acid conditions was possibly retarded by a thin amorphous silica layer formed on the CsMP surfaces. Such characteristics of the dissolution are consistent with that of silica-rich glass. To infer the dissolution behavior of CsMPs in the human body, the dissolution rate in Ringer's solution at 37 °C was estimated as 1.00 ± 0.37 μm/year. [ABSTRACT FROM AUTHOR]

After the Fukushima nuclear accident in Japan, whether the structural safety of the nuclear power plant (NPP) can be guaranteed under an earthquake has been of wide concern. Automatic seismic trip systems (ASTS) have been deployed in NPPs. There are generally two units or more double units on the one NPP site, and the vibration energy of the structure can certainly affect its adjacent structures through the soil, and there is energy transfer and conversion between adjacent structures. At present, the distance between two reactors of NPPs of different reactor types is generally 100–200 m (this distance is referring to the distance between the centers of two reactors, which is slightly different for different reactor types). In the past, seismic instruments were used in the ASTS and the setting of shutdown threshold, so the impact of only one unit was considered in the structural analysis of NPPs, and the interaction of two reactors through site conditions was not considered. In addition, as the site conditions of NPPs become more and more complex, it is necessary to consider the impact of one reactor structure on another reactor structure through the soil on the same site under an earthquake. In order to analyze the influence of structure–soil–structure interaction (SSSI), a three-dimensional refined finite element model of NPPs is established in this paper. The soil–structure interaction (SSI) is considered by using viscoelastic boundary. The seismic responses of different positions of the raft foundation and NPP structure, under the conditions of considering SSI effect (one reactor) and SSSI effect (two reactors), are compared. The influence of SSSI effect on the seismic responses of the raft foundation and NPP structure is revealed. It is proposed that SSSI effect should be reasonably considered according to the site conditions for the structural analysis of NPPs for the NPP ASTS. [ABSTRACT FROM AUTHOR]

This article analyzes methods and technologies for assessing the way of formation, composition, characteristics, and features of corium, i.e., a mixture of nuclear and structural materials of a nuclear reactor core, which formed as a result of an accident that is accompanied by partial or complete melting of the core. The analysis is based on data from studying the corium formed as a result of the accident at the Fukushima Daiichi nuclear power plant, which are in the public domain and are the result of the work of many scientific organizations around the world. The study of corium is a main problem in improving nuclear safety in the future and an objective in developing the successful procedure for eliminating the consequences of the accident at the Fukushima Daiichi nuclear power plant. Without a detailed analysis of the neutron physics, materials science, gravimetric, and other characteristics of the corium and without creation of a corium data set that combines these characteristics, it is impossible to create a full fledged model of the corium in the future and to organize an efficient and safe process for removing nuclear materials from the damaged units of the Fukushima Daiichi nuclear power plant. This study is aimed at combining the existing research results into a data set, which can later be used to simulate the corium using neutron physics codes. The set being created includes data, such as the size, density, and morphology of corium samples and their approximate nuclide composition. The created data set will allow one not only to perform tasks related to increasing the level of safety when accomplishing the procedure for eliminating the consequences of the accident at the Fukushima Daiichi nuclear power plant through simulation but also will serve as a basis for creating an international benchmark for simulating a mixture that contains nuclear materials (NMs). [ABSTRACT FROM AUTHOR]

In the course of the Fukushima nuclear accident, radionuclides were released in various forms, including so-called radiocesium-bearing microparticles (CsMP). So far, four types of CsMP were described: Type A is smaller in size (< 10 μm), Types B, C, and D are larger (> 100 μm). In this work, we present a novel type of CsMP (proclaimed Type E). Three particles of Type E were extracted from a contaminated blade of grass that was sampled 1.5 km from the Fukushima Daiichi nuclear power plant in late 2011. They were located using autoradiography, isolated using an optical microscope and micromanipulator, and characterized using scanning electron microscopy, energy dispersive x-ray spectroscopy, and low-level gamma-ray spectrometry. Type E CsMPs are 10–20 μm in size and exhibit an unusually low and barely detectable 137Cs activity of only ≤ 10 mBq per particle. Their brittle and fragile character may indicate a high surface tension. [ABSTRACT FROM AUTHOR]

After the Great East Japan Earthquake and the aftermath of the Fukushima Nuclear Disaster, Yōko Tawada has written many works that touch the issues surrounding earthquakes and natural disasters - she raises salient questions through the power of literature. The novel The Last Children of Tokyo, which will be examined in this study, is a dystopian novel written by Yōko Tawada after her trip to the disaster zone of Fukushima. The novel presents a society which was impacted by ecological disasters and environmental problems - a life of drifting into dystopia, taking place in the capital city of Tokyo the center of Japan's industry and economy. Tawada's novel leads us to a confrontation with today's human questions; on environmental problems, the danger of nuclear radiation, and the relationship of nuclear power plants to civilization. In this regard, Tawada's text was analyzed through the concept of "deep ecology" that emerged in the field of ecocriticism. The term "deep ecology" was first used by the philosopher Arne Naess in his 1973 article titled, Deep Ecology Movement: Some Philosophical Aspects. Explaining the basic principles of deep ecology into eight items, Naess provides a defense for the richness and diversity of life forms and states that human and non-human beings are values in themselves. The Last Children of Tokyo, emphasizing the value of not only human but also non-human beings, defending the equality of all beings and depicting all beings as part of the web of life has shown that it is compatible with the basic principles of Naess's philosophy of deep ecology. [ABSTRACT FROM AUTHOR]

The concept and methodology of traditional Defense in Depth (DID) was challenged in the Fukushima nuclear accident. In order to fix the weakness of the traditional emergency strategies of nuclear power plants (NPPs) and to enhance the DID for nuclear safety, the U.S. Nuclear Energy Institute (NEI) put forward the concept of Diverse and Flexible Coping Strategies (FLEX) for the special purpose of beyond-design-basis external event (BDBEE) hazard mitigation and the corresponding FLEX support guidelines (FSG). The theory has been wildly spread and accepted by many countries that generate nuclear power. The research on the FLEX strategy is a new trend in nuclear engineering in the recent decade. It provides not only fixed on-site equipment/devices but also on- and off-site portable resources to strengthen the reliability of the nuclear safety system, especially for the disaster/hazards (similar to the Fukushima nuclear accident) triggered by BDBEEs. After a brief introduction of the FLEX strategy, four opportunities and ten challenges are summarized. Subsequently, in view of these challenges and technical difficulties, five suggestions for future work are recommended. [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]

Large-scale decontamination work has been carried out in the aftermath of the Fukushima Daiichi nuclear power station accident in Japan in 2011. The soil that was removed and the wastes that were generated during the decontamination will be finally disposed of outside Fukushima Prefecture by 2045. To ensure successful and socially acceptable implementation of this final disposal process, it is essential to have a good understanding of what is considered important by the public. We used a choice-based conjoint analysis in the form of a web-based questionnaire to examine the relative importance of several factors in the choice of the final disposal sites of the removed soil and incinerated ash of the wastes. The questionnaires covered four attributes and 12 levels, namely the distance between the disposal site and a person's residential area, procedural fairness (decision process), distributive fairness (direct mitigation of inequity through multiple siting locations), and the volume and radioactivity of the substances to be disposed. Responses were received from 4000 people nationwide, excluding Fukushima residents. The results showed that the respondents gave high importance to choosing sites that were far from residential areas and to the two types of fairness, especially distributive fairness. The respondents showed no preference for the volume and radioactivity. This indicates that the public cares about the fairness of the siting for the final disposal sites and feels uncomfortable with plans for a final disposal site located close to them. Distributive fairness is necessary to pursue consensus in addition to procedural fairness. [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]

Objective: This study continues former studies on perinatal mortality in Japan after the Fukushima Daiichi nuclear power plant (FDNPP) accident in March 2011. An increased study region is chosen, and the study period is extended to 2019. Methods: Japanese monthly perinatal mortality data are provided on a prefecture level by the Japanese government. The study region consists of 12 prefectures around the FDNPP; the rest of Japan is used as the control region. A combined non-linear regression of perinatal mortality rates in the study- and control regions is conducted. The regression model allows for a common asymptotic lower limit of perinatal mortality, seasonal variations, and periodic peaks in 2012–2019 in the study region. To determine the dependency of the effect on distance from the FDNPP, the study region is divided into four core prefectures and eight prefectures surrounding the core prefectures. Results: Perinatal mortality rates in the study region show a significant 6.4% (95% CI: 1.8%, 13.4%) overall increase in 2012–2019 relative to the trend in preceding years with no attenuation during 2012–19. The increase translates to 590 (165, 1226) excess perinatal deaths (p = 0.016). It is characterized by annual peaks with maxima in April. A 13.6% increase is determined in the four core prefectures and a 4.3% increase in eight prefectures surrounding the core prefectures. Before 2012, there is a peak around April 2011 and a decline in October 2011; another significant peak is detected in November 2012. In the 4 core prefectures, large increases are found in the first quarter of 2018 (+70%) and in May 2019 (+130%). Conclusion: This study finds periodic peaks in perinatal mortality in spring 2012–2019 in 12 prefectures of Japan surrounding the FDNPP. In light of massive increases in 2018 and 2019 in the four core prefectures, continued investigation of perinatal mortality in contaminated regions of Japan is recommended. [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]

After the Fukushima nuclear meltdown, the Angela Merkel government in Germany officially announced its decision to permanently shut down all of its seventeen nuclear reactors. In closer proximity to Fukushima, the Lee Myung-bak government in South Korea expanded its nuclear energy program with specific plans to construct more nuclear reactors in various locations and pursued more export opportunities. It was only in 2017 that the South Korean government, under President Moon Jae-in, announced a gradual phase-out of nuclear power plants in South Korea. What explains the contrasting paths of the German and South Korean nuclear energy programs in the immediate aftermath of the Fukushima nuclear disaster? Why did the same external shock prompt sudden policy reversal in Germany while it took six more years for South Korea to turn its course? While existing studies are helpful in accounting for the rise of particular energy policies, they are insufficient for explaining the causes and specific timing of major policy reversals in the face of external crises. Building upon the literature on political opportunity structures, this article argues that the emergence of new political opportunities and the shift in political framing with respect to nuclear energy caused nuclear phase-out in both countries. A closer look at the two national cases offers an opportunity to delineate the domestic political process of nuclear energy policymaking and evaluate the role of exogenous shocks, such as a major nuclear disaster, in shifting political opportunity structure and reshaping the perceptions of energy security and political risks. [ABSTRACT FROM AUTHOR]

On 16 March 2021, the Teach311 + COVID-19 Collective () hosted a virtual roundtable discussion entitled "Sources of Disaster: New Epistemic Perspectives in Post-3.11 Japan." The event brought together scholars and students researching the history and anthropology of Japan to explore how the earthquake, tsunami, and nuclear power plant disaster of 11 March 2011 (3.11) changed our ways of knowing the world. The roundtable focused on the idea of the "source" to get at these epistemic shifts in lived experience and practical knowledge as well as historiography, and to investigate ideas that range from what we can know about acceptable risk and safety to notions of home and belonging. "Source" is a way to think about origins, but also the materials—texts, media, or testimony—that we collect and analyze to give rise to new or better knowledge. Building upon previous Teach311 activities that explored the roots of 3.11 and genba, participants in this roundtable expanded upon the significance and meanings of the notion of a "source" relative to the politics of epistemology in their research and studies in order to examine what reconstruction means in history when it is conducted alongside recovery. [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]

Emergency response planning associated with written procedures play a key role in the process safety to ensure that accident can be properly managed. Although the extensive use of digital techniques have significantly reduced the accident risk by early warnings and operation guidance, the Fukushima nuclear disaster reminds us that the unexpected events may still exceed existing system capability to indicate appropriate responding measures. A novel digitalized approach is hence required for planning decision support. This article presents a joint utilizing of two modeling and analysis methodologies, which are complementary to each other to provide comprehensive insights for decision-making in the accident emergency response. Multilevel Flow Modeling (MFM) is applied to develop an intelligent reasoning system, which can harness plant's qualitative functional knowledge to search available equipments and corresponding action sequences potentially being able to manage the accident. Go-Flow is a success-oriented reliability analysis method specially suitable for quantitative risk assessment in the situations involving configuration changes. The underlying configuration of each MFM-driven emergency response measure will update the understanding of goal achievement and modify the Go-Flow chart, by which plan's effectiveness of risk reduction can be evaluated. Moreover, Go-Flow is also used to conduct the risk matrix assessment for identifying critical components, which can provide a reference for effective assignment of resources in the long-term accident management. This work is expected to strengthen operator's ability of emergency response planning from perspective of both measure development and optimization. An accident scenario similar to what occurred in the Fukushima Daiichi nuclear power plant has been used to demonstrate the application of the propose approach. [ABSTRACT FROM AUTHOR]

Summary: The Extensive Damage Mitigation Guideline (EDMG), which was developed by the U.S. Nuclear Energy Institute (NEI) owing to the motivation of 911 terrorist attacks and not allowed to spread before the Fukushima nuclear accident, was publicly available after Fukushima nuclear accident and paid attention to worldwide. Many countries have adopted the U.S. EDMG methodology and developed their strategies (some are not called EDMG but have similar functions), planning to introduce it into the emergency plans of their domestic nuclear power plants (NPPs). Based on the defense‐in‐depth (DID) concept of nuclear safety, the experience of the Fukushima nuclear accident, and the state‐of‐the‐art of EDMGs research, this paper will give a comprehensive review of EDMG. To illustrate the reason for the introduction of EDMG into the traditional NPP procedures/guidelines, the review work started from the perspective of DID in nuclear safety and the reason for the Fukushima nuclear accident from the viewpoint of DID, which showed the weaknesses of DID implementation strategy ‐ underestimation of the damage during a beyond‐design‐basis external event (BDBEE). EDMG is crucial complementary for the old framework of procedures/guidelines to enhance the concept of DID. The research progress of EDMG in different countries has been reviewed and a rough comparison has been made among them according to the present state‐of‐the‐art from literature. The methodology of EDMG is summarized as follows: (a) Loss of Large Area (LOLA) ‐ the originally designed scenario for EDMG; (b) elements of EDMG ‐ the summarized contents for EDMG implementation; (c) classification of EDMG ‐ initial response EDMGs and Technical Support Center (TSC) response EDMGs; (d) implementation of EDMG‐introduction of three phases of EDMG implementation step by step. Furthermore, three typical methods to integrate EDMG into the traditional procedures/guidelines are reviewed. Finally, this paper gives some concluding remarks for EDMG‐related critical issues and recommended future work, which may be challenges for the development and application of EDMG and useful for the related researchers. Novelty Statement: The studies of the extensive damage mitigation guideline (EDMG), its methodology, and the progress in different countries have been reviewed.Three typical methods to integrate EDMG into the traditional procedures/guidelines are summarized and reviewed.Concluding remarks for EDMG‐related critical issues and recommended future work are summarized. [ABSTRACT FROM AUTHOR]

In response to a station blackout accident similar to the Fukushima nuclear accident, China's Generation III nuclear power HPR1000 designed and developed a passive residual heat removal system connected to the secondary side of the steam generator. Based on the two-phase natural circulation principle, the system is designed to bring out long-term core residual heat after an accident to ensure that the reactor is in a safe state. The steady-state characteristic test and transient start and run test of the PRS were carried out on the integrated experiment bench named ESPRIT. The experiment results show that the PRS can establish natural circulation and discharge residual heat of the first loop. China's Fuqing no. 5 nuclear power plant completed the installation of the PRS in September 2019 and carried out commissioning work in October. This debugging is the first real-world debugging of the new design. This paper introduces the design process of the PRS debugging scheme. [ABSTRACT FROM AUTHOR]

Background: After the Chernobyl accident on 26 April 1986, a drop in birth-rate was found in several European countries in the first quarter of 1987. The objective of the present study was to investigate whether a similar drop in live births occurred in Japan after the Fukushima nuclear accident. Data and methods: A study region was defined consisting of Fukushima prefecture plus 10 nearby prefectures. The observed monthly numbers of live births (LB) in October 2011 through December 2012 were compared with the predicted numbers determined from the trend of live births in the remaining months from January 2006 through December 2018. The study region was divided into Fukushima plus three adjacent prefectures (Area A, assumed effective mean dose in the first year 1 mSv) and seven surrounding prefectures (Area B, 0.5 mSv). The rest of Japan (Area C) served as the comparison (control) region (0.1 mSv). A combined regression of live births (LB) in areas A, B, C was conducted with individual trend parameters but common parameters for monthly variations. Results: In the study region as a whole (areas A and B combined) a highly significant 9.1% (95% CI: -12.2%, -6.0%) drop in LB was found in December 2011. Reduced numbers of live births were also observed in October-November 2011 (-3.3%, p = 0.006), i.e. in births exposed early in pregnancy. In the second quarter of 2012, i.e. in live births conceived more than 3 months after the Fukushima accident, the decrease was greater (-4.3%, p < 0.001) than in the first quarter (-1.6%, p = 0.11). i.e. in those conceived within the first three months after the accident while no significant decrease was detected in the third (-0.7%, p = 0.44) and fourth (-0.5%, p = 0.62) quarters. The effect in Dec 2011 was greater in Area A with -14.0 (-17.6, -10.3) % than in Area B with -7.8 (-11.1, -4.5) % and non-significant in Area C with -1.3 (-4.2, +1.6) %, p = 0.38. The combined regression of the data in areas A, B, and C found a highly significant association of the effect in December 2011 with radiation dose. Conclusion: It is suggested that the observed drop in LB in December 2011 may reflect early deaths of the conceptus from high radiation exposure following the triple meltdown at the Fukushima Daiichi nuclear power plant on March 12–15, 2011. [ABSTRACT FROM AUTHOR]

• The water-robot is applied to the nuclear disaster area. • Complex algorithm is used for the Artificial Intelligence based modeling. • Machine Learning is incorporated with random sampling based modeling. • Remediation of the radioactive contaminated is analyzed by the robotics. It is analyzed for the water-robot which works in radioactively contaminated areas of nuclear accident sites where the core-melted accident in the Fukushima and Chernobyl disasters is the target modeling of controlling the behavior in the harsh areas by radiation. The radiation detector is a particular characteristic of the water-robot in the nuclear power plant (NPP)'s disaster areas in which the artificial intelligence (AI) algorithm is analyzed for the performance of the robot. A figure shows the comparisons of parameters in which Specificity and Accuracy are quite higher in the time step of 0.25 min. The normalized radioactivity is simulated in a time step of 0.25 min. The radioactive decay graph decreases in exponential form. Following the robot movements, the radioactivity decreases gradually showing the discrete oscillating. The system is easy to be designed, because the moving path by the radiation distribution, because the contaminated structures give the radiation data. [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]

In 1957, Japan launched its first experimental nuclear reactor, the JRR-1, in Tōkaimura (Ibaraki). The bedrock of the Japanese nuclear industry, it introduced the famed BWR technology--also used in the Fukushima Daiichi nuclear power plant--and the training of the future workers of a flourishing industry. Based on the premise that the Fukushima accident was in part caused by the nuclear village--a system created with the commissioning of JRR-1 reactor in Tōkaimura--this paper analyses how the national newspapers covered the launch of the first Japanese reactor, and how the remaining media records suggest that the Fukushima nuclear accident falls within the continuity of earlier policies. [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 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]

The absence of online radiation-monitoring systems (RMSs) has been observed in the case of the Fukushima nuclear accident. As the tsunami destroyed 23 of the 24 status-monitoring points, almost no relevant radiation dose measurement data were available. Rapid deployment of a mobile radiological unit that can quickly determine the activity and direction of the radioactive cloud spread on the ground or in the air can prevent unnecessary deaths and related financial losses. Although the design of the current generation of nuclear power plants (NPPs) incorporates features that minimize the risk of large radioactive releases outside the reactor, it is still important to focus on the development of systems that can mitigate the consequences of such events. In situations when the level of radiation does not permit the personnel to perform the required measurements, online unmanned RMSs may come into play. For such a purpose, the RMS-00x RMS could be used, which is a modular system covering the functionality of dose rate measurement, air sampling, and radiation map creation without requiring human personnel to be present at the measurement site. The main purpose of the RMS-00x RMS is the rapid deployment of unmanned monitoring devices to reduce the radiation burden on workers and on public. The system can be applied in the vicinity of an NPP or at any location, where the source of ionizing radiation could be present. Before this system is used in real conditions, its components must be thoroughly calibrated, based on certified measurement equipment and the state-of-art simulation tools. This article deals with the description of the RMS-00x sensor modules and demonstrates their functionality in combination with unmanned aerial vehicles (UAVs). In addition, the use of the developed technology was demonstrated as part of the regular emergency planning and preparedness exercise of Jaslovksé Bohunice NPP (EBO NPP) on October 26, 2017. [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]

The Fukushima nuclear accident poses a new challenge for Probabilistic Risk Assessment (PRA) to consider the integrated risk of a nuclear power plant having more than one units. That calls for new technologies in the area of accident sequence modelling which traditionally deals with the accident in one reactor only. It has been shown that multi-unit event trees tend to be huge and consume a lot of manpower. This paper presents a rapid approach to generate multi-unit event trees based on tree combinational calculation, which leverage the existing event trees that have been built in single unit PRA. The combinatorial calculation is driven from the vector representation of event trees and can screen out the invalid combinations automatically by applying the proposed principles. A case study is presented in this paper with a nuclear power plant having 2 reactor modules under the Loss-Of-Offsite-Power initiating event to demonstrate the feasibility of the approach. The proposed approach has been realized by the software MUETBASE which can significantly improve the working efficiency and correctness of multi-unit event tree modelling. • The proposed method can help to evaluate the risk of plants with multiple units. • A multi-unit event tree generation method by combining single-unit ones is proposed. • The combinatorial calculation is realized via a vector representation of event tree. • Principles for screening valid combinations are provided. • A case study is also presented to demonstrate the feasibility of this method. [ABSTRACT FROM AUTHOR]

In this study, we have investigated the spray system's capabilities to reduce fission products in the containment atmosphere and control the containment pressure in a VVER-1000 nuclear power plant. Large Break Loss of Coolant Accident (LB-LOCA) without access to the active part of the Emergency Core Cooling System (ECCS), as a worst-case severe accident, has been investigated as a case study. Only containment is simulated via the MELCOR code, while leakage of various materials from the nuclear power plant's core and the primary circuit is considered as the boundary conditions. Following the Fukushima accident in 2011, many nuclear safety regulatory organizations focused on using portable equipment that is essential for decay heat removal in nuclear power plants during severe accidents. Based on the literature studies, the accident management scenarios have changed recently since severe accidents inside nuclear power plants have worried many scientists and the public. Evaluating the current spray system in a severe condition based on which this system was not designed is vital and novel. We considered that the spray system would be fully restored and perform its safety function using the existing portable equipment to depressurize the containment and deposition of the fission products. To calculate the maximum allowed delay time of the spray system recovery, the accident was modeled without the operation of the spray system while a safety criterion was considered to avoid reaching the ultimate pressure of containment. For a more detailed evaluation of the spray system, two different operating modes including the activation of one spray train and the activation of both spray trains have been selected. According to the obtained results, if the spray system is revived before 4,000s from the beginning of the accident, this system would be able to reasonably mitigate the accident consequences. Moreover, without the need for any external water supply source for the spray system, this system can be permanently fed from the containment sump for at least 800,000s after the initiation of the accident, requiring the relevant heat exchanger of the spray system to be recovered for this period. • Containment is modeled by the MELCOR code to investigate the ex-vessel phenomena. • Design-based LB-LOCA is modeled to validate the containment and spray system model. • Spray system capabilities during a combination of LB-LOCA and SBO are evaluated. • The spray system can preserve the containment integrity during the severe accident. [ABSTRACT FROM AUTHOR]

De novo mutation frequency in two Japanese tree species as a function of ambient radiation dose rate. [Display omitted] • Trees in contaminated areas following a nuclear accident were surveyed genetically. • De novo mutations (DNMs) were detected via RADseq, comparing parents and offspring. • Low-dose-rate radiation (up to 6.86 μGy h−1) did not affect the occurrence of DNMs. • Unknown factors other than low-dose-rate radiation had stronger effects on DNMs. • Haploid or phased reference genomes were effective for detecting DNMs. The impact of low-dose-rate radiation on genetics is largely unknown, particularly in natural environments. The Fukushima Dai-ich Nuclear Power Plant disaster resulted in the creation of contaminated natural lands. In this study, de novo mutations (DNMs) in germ line cells were surveyed from double-digest RADseq fragments in Japanese cedar and flowering cherry trees exposed to ambient dose rates ranging from 0.08 to 6.86 μGy h−1. These two species are among the most widely cultivated Japanese gymnosperm and angiosperm trees for forestry and horticultural purpose, respectively. For Japanese flowering cherry, open crossings were performed to produce seedlings, and only two candidate DNMs were detected from uncontaminated area. For Japanese cedar, the haploid megagametophytes were used as next generation samples. The use of megagametophytes from open crossing for next generation mutation screening had many advantages such as reducing exposure to radiation in contaminated areas because artificial crossings are not needed and the ease of data analysis owing to the haploid nature of megagametophytes. A direct comparison of the nucleotide sequences of parents and megagametophytes revealed an average of 1.4 candidate DNMs per megagametophyte sample (range: 0–40) after filtering procedures were optimized based on the validation of DNMs via Sanger sequencing. There was no relationship between the observed mutations and the ambient dose rate in the growing area or the concentration of 137Cs in cedar branches. The present results also suggest that mutation rates differ among lineages and that the growing environment has a relatively large influence on these mutation rates. These results suggested there was no significant increase in the mutation rate of the germplasm of Japanese cedar and flowering cherry trees growing in the contaminated areas. [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 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]

One month after the TEPCO accident, the number of the disaster-related deaths in Fukushima Prefecture exceeded that in Miyagi and Iwate which were not affected by the radiation, due to increase in disuse syndrome during the prolonged evacuation by the accident. About 90% of the deaths were the elderly. The risk and benefit of the evacuation of 11 municipalities in Fukushima are analyzed using data published by the Japanese government. The total loss of life expectancy (LLE) of the disaster-related deaths is 5,100,000 person-days. The LLE avoided by the evacuation is estimated from the cumulative doses of 172 locations. The average cumulative dose avoided is 205 mSv in 10 years. Total LLE avoided for 100,000 evacuees is 1,850,000 person-days. It is 2.8 times less than that accompanies evacuation. The delay in lifting the evacuation orders caused many disaster-related deaths among the elderly. The long-term evacuation of the TEPCO accident followed the dose rate recommended by ICRP, but is not justified. Discussions are provided for future improvements: (1) Lifetime fatal cancer probability from radiation exposure in the elderly is one-fifth of the average. Current guidelines do not take that into account. The difference needs to be incorporated into the nuclear emergency guidelines. (2) Radiation protection measures cannot describe other health risks, but the present guides are developed from the perspective of radiation protection. (3) Need to revise emergency guides to consider other health risks such as disuse syndrome of Fukushima, unnecessary abortions of Chernobyl and mental and psychological problems. (4) Risk communication with the general public does not work in a nuclear accident. (5) Exempt the ALARA principle from the public in low-dose area in the event of a nuclear accident. (6) Allow evacuees to participate in decontamination and restoration work. The lesson is important for countries where nuclear power plants are located in agricultural areas and are aging. • Cost benefit analysis shows higher evacuation risk than avoided at TEPCO accident. • Delay in lifting evacuation orders increased deaths of the elderly in Fukushima. • Consider low life time fatal cancer risk of old people in protective action guides. • Revise nuclear emergency guides to consider public health risks other than radiation. • Exempt public from as low as principle of radiation protection in a nuclear accident. [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]

• Evacuation plans need to be tailored to the type of resident with specific considerations for vulnerable people. • Information and instructions should be provided in the event of a nuclear accident. • Necessary resources for the sheltering option need to be secured with the support from the governments. • Coordinated approaches for the case of a long-term relocation. • Plans for lifting evacuation need to be carefully determined with the involvement of stakeholders. Standards and guidelines for preparedness and response in the case of a nuclear accident cover radiation protection, health management and communication with affected populations. Decision makers use these recommendations to decide on measures that protect people residing around a nuclear power plant that suffers an accident from radiation exposure; for example, sheltering, evacuation and relocation. While technological and radiological criteria exist for these protective measures, studies on past radiological and nuclear emergencies have shown that evacuation and relocation result in serious health effects; this needs to be considered in accident preparedness and responses in the future. Within the framework of the Nuclear Emergency Situations Improvement of Medical and Health Surveillance (SHAMISEN) (Ohba et al., 2020), a critical review of recommendations and experiences of previous major nuclear accidents was conducted, and the current paper focuses on the lessons learned about evacuation and relocation. We reviewed the contents of official documents and literature relating to the evacuation and relocation of residents, and to the evacuation of medical and other facilities in the three largest nuclear accidents to date: the Three Mile Island accident, Chernobyl accident, and Fukushima accident. We developed recommendations classified into the preparedness phase, early and intermediate phases, and recovery phase after an accident. In the cases of Three Mile Island and Fukushima, the evacuation area was set at 8–10 km from the nuclear power plant in the disaster prevention plan, and emergency responses, such as information provision and evacuation, had been developed only in this area. When the Fukushima accident occurred, evacuation beyond this area was urgently planned or instructed, resulting in marked confusion, such as forced multiple evacuations and relocations for long periods. Furthermore, information was lacking, and personal protective measures such as respiratory protection and iodine prophylaxis were not applied to evacuees. In hospital and facility evacuation, it became more difficult to implement evacuation owing to a lack of advance planning and support in the event of the accident. In Fukushima, more than 60 people in hospitals and nursing care facilities died during or soon after evacuation. In long-term relocation, in addition to continuing adverse mental effects, there were health effects relating to relocation, such as lifestyle-related disease. The return of residents to the evacuation area required many issues, such as a delayed recovery of the living environment, to be overcome in addition to measures to reduce the effects of radiation. Recommendations for evacuation in the SHAMISEN framework were developed (SHAMISEN Consortium, 2017; Liutsko et al., 2020) from these lessons of previous accidents. [ABSTRACT FROM AUTHOR]

• Innovative proposal in the application of CTM for a complex process accident. • Criteria selection by AHP for complex accident analysis methods comparison. • The INRS method characterizes each event in the evolution of the accident. • The INRS CTM results better than NUREG FTA for descriptive and consequential criteria. This article proposes a new approach to the Cause Tree Method (CTM) or also known as the INRS method (Institut National de Recherche et de Sécurité), with the aim of verifying its applicability for accidents in more complex environments, than they are often used, like work accidents. For this, the Analytic Hierarchy Process (AHP) methodology was used as a way of supporting the comparison with other accident investigation methods, in which, selected the most impacting criteria for the analysis of complex accidents. From which it allowed the comparison of the results of the analyses performed of the Fukushima accident by the NUREG - 0492 method and the INRS method.In addition, this is an innovative approach in the study of the Fukushima accident, since it makes it possible to know the influences of the main components in the occurrence of the accident and the spread of damage. It was observed that the INRS method obtains an advantage over the NUREG - 0492 method in 2 criteria of the 3 criteria selected as relevant in the investigation of complex accidents. In addition, to the analysis made of the accident, it is understood that although the geographic location of the nuclear station anticipates the occurrence of earthquakes and subsequent tsunamis, safety plans were inefficient to contain the damage. Thus, it is verified, through the comparative analysis between methods and case study, that the INRS method is a robust and viable option to assess complex accidents. [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]

• The bending stress of pre-hydrided Zry-4 cladding tube following LOCA has been investigated. • The maximum bending stress decreased by hydrogen absorption. • The decrease in the maximum bending stress was mainly determined by the hydrogen concentration after simulated LOCA test. • The maximum bending stress at a hydrogen concentration of 1500 ppm was estimated to be about a half of that at 0 ppm. After the accident at Fukushima dai-ichi nuclear power station, the fracture resistance of fuel rods against aftershock became a concern in the safety evaluation of reactor core during the long-term cooling after a loss-of-coolant-accident (LOCA). In this study, the maximum bending stresses of pre-hydrided cladding tubes which experienced simulated LOCA tests were investigated. The obtained results suggested that the decrease in the maximum bending stress of the cladding tube experienced LOCA conditions was mainly determined by the hydrogen content in the cladding tube after simulated LOCA test, irrespective of initially hydrogen content. It was also suggested that the decreasing trend of the maximum bending stress with the increasing hydrogen content would be expressed by a form of exponential function, in which the maximum bending stress at a hydrogen content of 1500 ppm was estimated to be about a half of that at 0 ppm. [ABSTRACT FROM AUTHOR]