Fukushima Nuclear Accident Research Articles

Social networks and posttraumatic stress symptoms five to ten years after the Fukushima nuclear power plant disaster

Since the 2011 Fukushima nuclear power plant accident, multiple social network disruptions have been reported among the community in Fukushima, while posttraumatic stress symptoms among the residents have persisted. In this study, we aimed to explore the influence of time and social networks on the recovery of posttraumatic stress symptoms based on longitudinal data from community residents in Fukushima, following up five to ten years after the nuclear power plant accident. We conducted five questionnaire surveys quasi-annually, the targets of which were randomly sampled 4900 non-evacuee community residents. In this study, the data of 1809 respondents who participated in at least one survey were used (36.9% of the initial target). Setting posttraumatic stress symptoms as the outcome, we examined the interaction between time and social network size using a mixed model, adjusting for sociodemographic characteristics and disaster-related events. Their interaction was statistically significant, and the posttraumatic stress symptoms of those with small social networks persisted, while those with larger social networks recovered. Maintaining and promoting social networks may contribute to mental health recovery after a nuclear disaster.

Issues Related to the Passing Down of the Experience of the Fukushima Nuclear Accident and Environmental Education: Recent Initiatives of the Fukushima-Project Research Group

Issues Related to the Passing Down of the Experience of the Fukushima Nuclear Accident and Environmental Education: Recent Initiatives of the Fukushima-Project Research Group

Transport and fate of Fukushima-derived 137Cs and 134Cs in the seawater of theNorthwest Pacific in 2015.

To understand the influence of the Fukushima accident on the Northwest Pacific, the distributions and transportations of 134Cs and 137Cs in the seawater in the Northwest Pacific in May and September 2015 were studied. The data showed that the Fukushima-derived 134Cs and 137Cs at some stations can still be distinguished from background level ~ 4years later. On the whole, the activities of 137Cs and 134Cs in seawater were decreasing from May to Sep 2015. But the increased inventories and the surface activities of 137Cs imply that there has ever been an extra 137Cs from offshore water transported to this study area (from 31° N to 27° N, 145° E to 152.5° E) in May 2015. The average activities of 137Cs in subtropical gyre area in south of KE were the highest and the least were to the east of Luzon Strait in 2015. In vertical direction, 137Cs in subtropical gyre area were mainly distributed at 100 ~ 500m layer and 137Cs only at 500m layer in this area showed an increasing trend from May to Sep 2015 which reflects more 137Cs were still penetrating to deeper layer of 500m from upper water. But they were almost not found below 1000m layer. It was associated with the subsurface transport of radiocesiums by Northwest Pacific Mode Water (NPMW) and the diffusion of mesoscale eddy. Different distribution characteristics of 137Cs existed between north of KE and south of KE. The low-temperature-low-salinity water mass likely to be the first Oyashio Intrusion was the main factor that resulted in higher 137Cs appearing at the upper 100m layers in north of KE.

Robotics uncharted: When hazardous-duty robots met the Fukushima nuclear disaster (2011–2015)

The Fukushima nuclear disaster of 11 March 2011, created a hazardous environment for both residents and rescue workers. The proficient use of robotic technology to assist with disaster mitigation and intense research into this genre of robotics had been proposed as a pivotal substitute for endangering disaster workers in disaster response. However, despite the high expectations and aspirations of Japan’s competitive robotics industry, the technological and political problems surrounding the use of robots were severe. Robot-enabled disaster management can only materialize through effective policy direction by the government. This paper explores the problems of using robots in disaster management since Japan’s launch of a nuclear disaster-response robot project in the 1980s.

Improving the estimation of direct release rates and transport processes from the Fukushima Daiichi Nuclear Power Plant accident using higher-resolution oceanic dispersion model

A series of accidents at the Fukushima Daiichi Nuclear Power Station (F1NPS), following the 11 March 2011 earthquake and tsunami, resulted in the release of radioactive substances into the ocean. In particular, the release of large amounts of radioactive caesium has damaged the fishing industry, leading to voluntary restrictions on fishing and shipping. Oceanic dispersion simulations based on estimates of the pathways and fluxes of radioactive materials provide useful information for assessing the environmental impacts and formulating measures to mitigate the effects of the accident. For the direct release rate from the F1NPS site, an estimation method was developed using the results from nearby monitoring, and the seawater exchange rate was estimated in target volume using a numerical simulation. However, the influence of volume on the seawater exchange rate was not considered. Appropriate volumes must be considered when estimating the effects of future accidents. In addition, the directional coastal transport was underestimated in the simulations of the F1NPS accident because of the low resolution. To estimate the pathways and fluxes of radioactive material to the ocean and understand the distribution of the concentration of radioactive material based on ocean dispersion simulations, a study was conducted using a higher-resolution model. The horizontal resolution of the conventional ocean dispersion model Regional Ocean Modelling System (ROMS), was increased from 1 km to 200 m. The optimal settings of the seawater exchange rate were investigated, and the radioactive caesium transport process in the coastal direction was more accurately reflected. We found that the conventional volume for determining the seawater exchange rate, including the locations of release sources and observation points, is optimal. The validity of this finding was confirmed using experimental equations from previous oceanic tracer release experiments. To estimate future release rates, it an appropriate volume must be defined, for example, depending on the distance between the locations of the release sources and the observation point. In addition, improvements in the accuracy of the simulation of the coastal transport process were observed owing to the higher resolution, which increased reproducibility. However, with a horizontal resolution of 200 m, problems with repeatability near the harbours arose. A higher resolution, achieved using nesting or other methods, would be desirable to deal with releases smaller than those in the F1NPS accident.

Analysis of the Long-Term Interaction Between Molten Core and Dry Concrete at Fukushima Daiichi Unit 1

The latest investigations of Fukushima Daiichi Unit 1 have demonstrated that corium attack to the pedestal walls and pedestal floor has occurred in Fukushima Daiichi Unit 1 to a certain extent. The results of past analytical benchmarks, such as the Organisation for Economic Co-operation and Development (OECD)/Nuclear Energy Agency (NEA) Benchmark Study of the Accident at the Fukushima Daiichi Nuclear Power Plant (BSAF project), have agreed with this finding. However, the latest investigation does not show evidence of unlimited molten core–concrete interaction (MCCI), which is one of the main discrepancies from the BSAF project. More recently a MCCI benchmark has been launched in the context of the OECD/NEA project ARC-F (Analysis of Information from Reactor Building and Containment Vessels of Fukushima Daiichi Nuclear Power Station). In the benchmark, common geometry, boundary, and initial conditions have been selected among all the participants. The results show an improved agreement among different codes for what concerns overall erosion, corium temperature, and hydrogen generation, confirming that to some extent, the earlier scatter found in these variables came from differences in the MCCI scenario modeled by each partner. However, common unlimited erosion, not observed by onsite visual inspections, is still predicted. Understanding the origin of this deviation might provide insights into boundary conditions, model drawbacks, or ill-posed assumptions that might need to be revisited (e.g. interfacial temperature, effective heat transfer coefficients, concrete heat transfer). In this paper, a summary of the overall results and a discussion of modeling and boundary conditions is presented to disclose the results of the activity and the future steps to be taken in the OECD/NEA project FACE (Fukushima Daiichi Nuclear Power Station Accident Information Collection and Evaluation).

Embodying the nuclear: The moral struggle of family care in postfallout Japan

AbstractThis paper examines the moral struggle of family care by focusing on parents’ efforts to raise “healthy” children in irradiated environments of Fukushima following the 2011 Fukushima Daiichi nuclear disaster. Drawing on fieldwork between 2017 and 2020, it explores the lived experiences of primary caretakers, mostly mothers, as they strive to cultivate “health” in their children while negotiating conflicting logics of radiological exposure, risk assessment, and gendered childcare. Central to this endeavor is what I call an ethical labor of “balancing:” the daily negotiation between protecting children and allowing them to live fully in risk‐laden environments. Emphasizing intercorporeal and interpersonal aspects of embodied care, the paper examines the nuanced ways in which three mothers recalibrate notions of health, personhood, and responsibility to safeguard their children's everyday lives. Such notions of “health” carry significant implications for family dynamics amid the uncertainties of postdisaster life. By highlighting the critical role of family care in potentially stigmatizing environments, the paper advocates for developing frameworks that address the real‐life complexities of making life in an increasingly compromised world.

Resilience-based seismic design for nuclear island building: An innovative hybrid passive control system

The Fukushima nuclear incident has heightened global concerns about the safety of nuclear facilities, the imperative to enhance the seismic resilience of nuclear power plants (NPPs) has become a pivotal aspect of nuclear safety. This study introduces an innovative hybrid passive control system that integrates three-dimensional (3D) base isolation technology with periodic isolation walls, aiming to bolster the seismic resilience of NPPs against very rare earthquakes. Furthermore, a complete and viable computational procedure was developed to study the nonlinear soil-structure interaction effects with high-precision wave motion analysis. Finally, the efficacy of the innovative control system to improve the seismic resilience of large-scale nuclear island buildings situated on non-rocky sites was assessed. The findings reveal that the system significantly mitigates the distribution of damage to NPPs during very rare earthquake scenarios. Compared to non-isolated NPP, the adoption of a hybrid passive control system reduces structural damage dissipation energy by 97.73 %. The system augments the effectiveness of 3D base isolation technology in reducing dynamic responses; specifically, the floor response spectra at the top position of the nuclear island building in the X, Y, and Z directions were lowered by 62.33 %, 52.03 %, and 84.12 %, respectively. Moreover, the system considerably reduces the deformation of the 3D isolation bearings. The innovative hybrid passive control system helps to enhance the seismic resilience of NPPs.

Literature survey and analysis of phytoremediation strategies for Cs-137 decontamination

Phytoremediation has become a sustainable solution for mitigating cesium-137 (Cs-137) contamination and has been implemented in areas affected by the Chernobyl and Fukushima nuclear disasters. Despite the absence of nuclear power plants in Indonesia, incidents of Cs-137 contamination have been reported in Batan Indah Housing Complex, emphasizing the need for effective decontamination techniques. The aim of this study was to analyze the bibliometric characteristics of research works on phytoremediation in addressing Cs-137 contamination during the last ten years (2013–2022) by foreign and Indonesian authors. This research is important both globally and in specific contexts, such as Indonesia, particularly in the context of policy and practical applications. For example, when facing issues like Cs-137 decontamination in the BATAN Indah area, the research can have local relevance and contribute to solving immediate problems. This study utilized the Scopus database and retrieved 2,123 article titles within this topic over the last decade. Several indicators were used to examine the publications: productivity of authors, collaboration between countries, top-cited articles, keywords analysis, and publication trends. The results show that the number of publications fluctuated over previous decade with an average publications age of 5.54 years. Onda Y from the University of Tsukuba, Tsukuba, Japan become the most prolific and collaborative author. Japan being the most productive and collaborative country, while Indonesia ranked 42nd with only 9 publications regarding the topics. The bibliometric analysis provides a foundation for understanding the development of science on this topic and uncovers that there is still plenty of space to conduct phytoremediation research in Indonesia, especially for Cs-137 contaminated soils, which have increased over the years.

Impacts of farmland decontamination on 137Cs transfers in rivers after Fukushima nuclear accident: Evidence from a retrospective sediment core study

Following the Fukushima Daiichi Nuclear Power Plant disaster in March 2011, the Japanese government initiated an unprecedented decontamination programme to remediate 137Cs-contaminated soils and allow population return. This programme involved the removal of topsoil under farmland and residential land, and its replacement with “fresh soil” composed of granitic saprolite. However, decontamination was limited to these two land uses, without remediating forests, which cover 70 % of the surface area in the affected region. In this unprecedented context, the specific impact of this unique decontamination programme on 137Cs transfers in river systems remains to be quantified at the catchment scale. In this study, based on the analysis of a sediment core collected in June 2021 in the Mano Dam reservoir draining a decontaminated catchment, the effects of soil decontamination on particle-bound 137Cs dynamics and sediment source contributions in response to a succession of extreme precipitation events were retrospectively assessed. The sequence of sediment layer deposition and its chronology were reconstructed through the analysis of several diagnostic properties (organic matter, elemental geochemistry, visible colourimetry, granulometry) and contextual information. During abandonment (2011–2016), cropland contribution decreased (31 %). Concurrently, 137Cs activity and deposition flux decreased (19 and 29%year−1, respectively). Following decontamination (2017), sediment transfer increased (270 %) in response to increased contributions from decontaminated cropland and “fresh soil” (625 % and 180 % respectively). Meanwhile, forest contributions remained stable. In contrast, 137Cs activity dropped (65 %), although 137Cs deposition flux remained constant. Forests acted as a stable source of 137Cs. Accordingly, 137Cs deposition flux after decontamination (2016–2021) was similar to that observed during the 5-years period of land abandonment (2011–2016), as a result of the regrowth of spontaneous vegetation over farmland, protecting soil against erosion. Future research should further investigate the impact of longer land abandonment that prevailed in some regions decontaminated lately on the 137Cs fluxes in the rivers.

Long-term evacuation and obesity: a 12-year follow-up comparative study of residents inside and outside Katsurao Village after the Fukushima nuclear disaster.

Evacuation, owing to a disaster, impacts various aspects of an individual's life, including health status. This study aimed to determine the prevalence of obesity among residents of Katsurao Village, Fukushima Prefecture, after the evacuation order due to the Fukushima nuclear disaster in 2011 was lifted in 2016 and to compare the prevalence of obesity by place of residence (inside or outside the village). The number of examinees, sex, age, place of residence, body mass index (BMI), exercise habits, smoking habits, drinking habits, and dietary status were extracted from the results of health checkups since 2016. We compared the BMI of the indigenes of Katsurao Village by place of residence (inside or outside the village) over time. Although 7 years have passed since 2016, ~70% of the registered residents of Katsurao Village still live outside the village. The obesity rates have consistently been higher among people living outside the village compared to those inside, and the place of residence was the only factor significantly associated with obesity. The findings of this study suggest early intervention is necessary to prevent health risks associated with disaster evacuation if the evacuation period is prolonged.

Attitudes toward future child-rearing among male and female adults without children in different prefectures at 11 years after the Fukushima Daiichi Nuclear Power Plant accident

This study aimed to determine whether confidence in future childbearing and child-rearing in relation to radiation exposure differs among people without children in Fukushima Prefecture, its neighboring prefectures (Tochigi, Ibaraki, and Miyagi), and other prefectures, and among men and women at 11 years after the nuclear accident. In February 2022, a cross-sectional online survey was conducted using an Internet research company. A total of 985 people were surveyed: 240 from Fukushima, 305 from neighboring prefectures, and 440 from other prefectures. The proportion of women who were confident about future childbearing was low and the confidence was associated with radiation-related risk perceptions in both Fukushima and neighboring prefectures. The results suggest that the more people want to have children in the future, the more likely they will be able to discuss radiation, and the less likely they will be able to believe that radiation has a low impact on their partners. Therefore, it is necessary to create an environment where people can openly discuss radiation, and to examine factors that affect confidence in future childbearing and child-rearing by gender and prefecture.

The Accident at Tokyo Electric Power Company Incorporated’s Fukushima Daiichi Nuclear Power Station: A Review of Radiation-Exposed Medical Care and Waste (Secondary Publication)

This review is based on articles published in <italic>Japanese Journal of Health Physics</italic> on “Radiationexposed medical care and waste” related to Tokyo Electric Power Company Incorporated (TEPCO)’s Fukushima Daiichi Nuclear Power Station accident. Here, we have considered three original articles; one technical data, one special article, one 50<sup>th</sup> anniversary article, one preface, three topics, and two cases of From Japan to the World (J to W). These articles have reported the system and standards that were established after the accident. Moreover, they have summarized rare experiences such as the fumbling response at the time and the evaluation of samples in that disaster. These articles constitute valuable records of the situation.

Absolute Method for Measuring Environmental Radioactive Materials Using Imaging Plates

Abstract We had previously developed a measurement method using an imaging plate (IP) to evaluate and address surface contamination caused by the release of radioactive materials during the Fukushima nuclear accident. The measurement units for the surface contamination density were in relative values [described as relative luminescence levels measured in luminescence arbitrary units (LAU)], but the evaluation was required in absolute values, such as Bq cm−2, to enable appropriate control of exposure doses. This study establishes a method for converting the IP measurements of surface contamination density due to environmental radioactivity into absolute values. Soil contaminated with radioactive materials from the Fukushima nuclear accident was collected to create a working reference material (WRM). The conversion coefficient for surface contamination density was calculated using the WRM values measured with an IP and high-purity germanium detectors. The IP measurement values were converted into the surface contamination density using the conversion coefficient. The WRM values measured with the IP and high-purity germanium detectors were 324.1 LAU and 32.22 ± 2.27 Bq cm−2, respectively. The surface contamination density conversion factor was calculated as 0.0994. The surface contamination density on the roof of the Tsukuba City facility was re-evaluated using the conversion factor. The average value of 29,972 Bq m−2 matched the amount of radioactive material fallen in Tsukuba City. By standardizing the measurement conditions for surface contamination when using IPs, we successfully quantified the surface contamination density with an accuracy comparable to that of conventional methods. This method is expected to make a significant contribution to efficient radiation safety management.

Chemical implication of the partition coefficient of 137Cs between the suspended and dissolved phases in natural water

After the Fukushima Daiichi nuclear power plant accident, the terrestrial environment became severely contaminated with radiocesium. Consequently, the river and lake water in the Fukushima area exhibited high radiocesium levels, which declined subsequently. The partition coefficient of 137Cs between the suspended sediment (SS) and dissolved phases, Kd, was introduced to better understand the dynamic behavior of 137Cs in different systems. However, the Kd values in river water, ranging from 2 × 104 to 7 × 106 L kg−1, showed large spatiotemporal variability. Therefore, the factors controlling the 137Cs partition coefficient in natural water systems should be identified. Herein, we introduce a chemical model to explain the variability in 137Cs Kd in natural water systems. The chemical model includes the complexation of Cs+ with mineral and organic binding sites in SS, metal exchange reactions, and the presence of colloidal species. The application of the chemical model to natural water systems revealed that Cs+ is strongly associated with binding sites in SS, and a major chemical interaction between 137Cs and the binding sites in SS is the isotope exchange reaction between stable Cs and 137Cs, rather than metal exchange reactions with other metal ions such as potassium ions. To explain the effect of the SS concentration on Kd, the presence of colloidal 137Cs passing through a filter is significant as the dominant dissolved species of 137Cs in river water. These results suggest that a better understanding of stable Cs dissolved in natural water is important for discerning the geochemical and ecological behaviors of 137Cs in natural water.

Progress in passive spent fuel pool cooling system R&D based on heat pipe technology

Following the Fukushima Daiichi Nuclear Power Plant accident, particularly the hydrogen explosion at Unit 4, the safety of spent fuel pools garnered heightened attention, and the global nuclear industry extensively studied post-accident cooling of spent fuel pools consequently. During this period, the distinguished passive capabilities of heat pipes led to their superior adoption as primary heat exchangers, gradually becoming a technical consensus in the whole field. Starting in 2016, based on the series of PEX (Passive Experimental Facility), the group led by China Nuclear Power Engineering Co., Ltd. (CNPE) commenced continuous research on heat pipe mechanisms, the design of separate plate heat exchangers, and the overall characteristics of the Passive Spent Fuel Pool Cooling System (PSFS). And in 2023, CNPE proposed the conceptual design for the Linglong One PSFS system finally. The PEX series experiments were completed in two phases using four sets of experimental apparatus: the feasibility study phase with PEX00 and PEX00+, smaller-scale experimental setups with heat power 2–10 kW, primarily addressing issues related to heat pipe mechanisms, working fluid selection, optimal filling rate, vacuum maintenance, system startup characteristics, and the engineering feasibility of separate heat pipe heat exchanger; and the prototype testing phase with PEX50K and PEX100K. PEX50K, a medium-scale conceptual prototype test facility with heat power 50–100 kW employing a novel separated plate heat pipe (SPHP), focusing on research on innovative heat pipe devices. PEX100K, a large-scale engineering prototype test facility with heat power 100–200 kW employing traditional separated tube heat pipes (STHP), aimed at performance verification of engineering prototype units. After five years of research, the SPHP-based approach was ultimately selected, while the initial one with STHP was discarded. This paper provides a comprehensive overview of CNPE's pioneering, exhaustive, and systematic research and development process on SPHP and PSFS. details the PEX series experimental apparatus, and presents the main conclusions. More detailed experimental data, discussions on specific phenomena in certain experiments, detailed descriptions of equipment's processes, and ongoing actual system-level tests will be discussed in subsequent papers.

Nuclear power plant biological complications on marine biota from a probabilistic accident – A case study

An accident at the Barakah Nuclear Power Plant (BNPP) would result in a significant radionuclide release into the semi-closed marine environment. In this research, the released radionuclide distribution pattern and dose rate in the Persian/Arabian (Gulf) were calculated using a combined hydrodynamic/radiobiological model. Simulations of the dispersion of artificial radionuclide concentrations were conducted using a HYSPLIT model. To assess prospective hazards in case of an incident, environmental risk from ionizing contaminants: assessment and management (ERICA) tools were used. Using the Fukushima nuclear power accident as a model, the scenario source term profile was developed. The volumetric concentrations levels of pollutants ranged between 1 × 104 mBq m−3 to 1 × 1010 mBq m−3 in the radius of 200 km after 48 h. Based on the dose rates of the various marine biotas, Polychaete worms, and Pelagic fish, they had the highest and lowest dose contribution.

Inversion of Critical Atmospheric 137Cs Emissions Following the Fukushima Accident by Resolving Temporal Formation from Total Deposition Data.

Understanding the transport of 137Cs emitted during the Fukushima accident is challenging because the critical emissions that produced the high-deposition area are not adequately resolved in existing source terms. This paper presents an objective inverse reconstruction of these emissions by fusing atmospheric concentrations with a-priori emissions extracted from total depositions. This extraction, previously considered impossible for complex real-world accidents, is achieved by identifying the critical temporal formation process of depositions in the high-deposition area and estimating the corresponding emissions by using an atmospheric transport model. The reconstructed source term reveals two emission peaks from 10:00-11:00 and 14:00-15:00 on March 15, which agree with the in situ pressure measurements and accident analysis, suggesting that they came from pressure drops in the primary containment vessels of Units 3 and 2, respectively. This finding explains the environmental observations of spherical 137Cs particles. The source term also objectively and independently confirms the widely used reverse estimate. The corresponding 137Cs transport simulations better match the various observations than those produced by other source terms, proving that the two-peak emission creates a high-deposition area. The proposed method outperforms the direct fusion of deposition and atmospheric concentration observations, providing a robust tool for multiobservation fusion.

An experimental study of the thermal-hydraulics of a spent nuclear fuel pool under loss-of-cooling accident conditions. Part II: a first interpretation of the MIDI tests

This article provides a first interpretation of the MIDI tests that were conducted in the frame of the IRSN’s DENOPI project. A first-level phenomenological analysis is detailed here. It is shown that the actual phenomenology mostly complies with the one that was envisioned by the community right after the Fukushima-Daiichi nuclear accident. Next, the diverse modes of water vaporization that may come into play during a spent nuclear fuel pool loss-of-cooling accident are quantified for each achieved test, by means of a proposed analytical model of the vapor diffusion process taking place on top of the liquid pool free surface. Then, a so-called vaporization regimes map is reconstructed on the basis of the test data. This map allows predicting the most likely dominant vaporization mode, given the pool level and total heat power. At last, the obtained data is reduced through the form of a set of dimensionless correlations, involving some of the classical numbers in heat and mass transfers. In doing so, the free surface evaporation, degassing of dissolved gaseous species and bubbles release processes are all modeled by means of a simple mathematical formulation.

MUPSA-based evaluation of portable equipment utilization for risk reduction in nuclear power plants: Framework and case study

Based on the lessons from the Fukushima accident, new strategies to mitigate the spread of accidents in nuclear power plants have been established that consider portable equipment. The diverse and flexible coping strategies (FLEX) and multi-barrier accident coping strategy (MACST) based on the utilization of portable equipment are being adopted in case of an extended loss of all AC power and loss of ultimate heat sink. In this context, the establishment of specific strategies for utilizing portable equipment has emerged as an important issue. This study proposes a multi-unit probabilistic safety assessment (MUPSA)-based evaluation framework consisting of several steps to quantitatively assess the reduction in risk from the use of portable equipment at a multi-unit site, which can provide a basis for establishing optimal portable equipment strategies. According to the framework, after first defining the scope of the evaluation, risk-significant types of portable equipment are selected and the scenarios are analyzed. Risk reduction is then evaluated using modified MUPSA models according to the deployment of the portable equipment. A case study was conducted for an internal loss of off-site power (LOOP) and seismic LOOP focusing on how to evaluate the effectiveness of portable equipment through the developed framework.