Tokyo Electric Power Company Research Articles

Tritium transfer from seawater into marine organisms TFWT.

Tokyo Electric Power Company, TEPCO, has started tritiated water release into the Pacific Ocean. In order to reduce unreasonable rumor caused by tritium release, flounder, abalone, and sarggasum were exposed to tritium enriched seawater, and time dependent Tissues Free Water Tritium (TFWT) concentration was measured. Estimating the concentration of Organically Bound Tritium (OBT) is important to assess tritium impact because it has a longer biological half-life than TFWT. Current models estimate OBT concentrations using TFWT concentration. Understanding equilibration time is critical for making accurate TFWT concentration predictions. TFWT intake rate was analysed by the compartment model.

The Relationship Between Years of Service and Traumatic Experiences Related to Radiation Among Local Government Staff Working Within 30 km of the Fukushima Daiichi Nuclear Power Station

An accident occurred at Tokyo Electric Power Company’s Fukushima Daiichi Nuclear Power Station (FDNPS) in March 2011, following an earthquake and tsunami. Local government staff members who worked in the area had a variety of experiences due to the accident, including trauma. This cross-sectional study was conducted to clarify the relationship between years of service and radiation-related traumatic experiences among 490 staff members in municipalities around the FDNPS exactly a decade after the accident. They were classified as <5 years, 5–10 years, and >10 years, relative to their lengths of employment. The experienced staff (>10 years of service) had a rich array of traumatic experiences, compared to those with less experience (<5 years of service). By contrast, the experienced staff had a lower SOC-13 score than those with less experience, and a higher percentage of them reported that their workload was greater than that imposed on other local government employees. The study results suggested that the experienced staff members who worked in the affected towns prior to the FDNPS accident have been burdened with a prolonged heavier workload, including radiation-related duties.

Reinvigorating radioactive wastewater to the ocean: Investigate the effect of board diversity on environmental corporate social responsibility in the context of Japan

The discharge of radioactive wastewater into the eastern ocean from the Fukushima Daiichi nuclear plant, a decision that comes from the Japanese government and TEPCO (Tokyo Electric Power Company), has subjected Japanese firms to reputational damage risks and increasing environmental legitimacy pressure from multiple stakeholders in environmental corporate social performance (ECSR) than ever. In the present research endeavor, we draw upon the existing body of scholarly literature pertaining to gender-diverse board and business ethics as a critical element of steering ocean and coastal environmental management. This undertaking aims to provide original insights into the factors influencing board gender diversity (BGD) and its subsequent impact on ECSR within the specific context of Japan. Grounded in the theoretical framework of legitimacy theory, we put forth a conceptual model designed to elucidate the relationship between BGD and ECSR. Additionally, this study delves into the moderating influence of financial constraints between BGD and ECSR. To empirically examine our conceptual framework, we collected data from two primary sources: Toyo Keizai Inc. and Nikkei Inc. The findings of our investigation reveal a statistically significant positive relationship between BGD and ECSR performance. Furthermore, our results indicate that financial constraints serve to intensify the association between BGD and engagement in ECSR initiatives. Finally, we corroborate the robustness of our findings through various extensions of our analytical models.

Consideration of the conversion factor from air dose rates to individual external dose per hour after the Fukushima accident—individual external dose measurements of a TEPCO employee in Fukushima prefecture over a 9 year period—

The accident at Fukushima Daiichi Nuclear Power Plant (FDNPP) in 2011 resulted in the dispersion of radioactive materials throughout the surrounding area and an increase in the air dose rate was even confirmed in Fukushima City, which is located approximately 60 km northeast of FDNPP. A Tokyo Electric Power Company (TEPCO) Holdings employee, who has lived and worked in Fukushima City since the FDNPP accident, measured individual external doses, GPS data, and his activities in Fukushima Prefecture over a 9 year period beginning in 2014. This data provides valuable information about the area. The data show the following results. (i) Comparison of the air dose rate at the home location to the individual external dose per hour at the home shows that the average conversion factor has increased over the 9 years and exceeded 0.3 since 2019, indicating an overall relatively good correlation. (ii) Individual external doses measured in the office on the fourth floor of a concrete structure in Fukushima City have not changed significantly from 2014 to 2022, when air dose rates showed a decrease. (iii) Outdoor individual external doses, such as those measured when commuting on foot, have a relatively strong correlation with air dose rates from airborne monitoring with the conversion factor of about 0.6. The conversion factor do not differ significantly from 2014 to 2022.In this study, the individual external dose data is applicable to the TEPCO measurer and is not necessarily representative of all residents of Fukushima City. However individual external dose data for 9 consecutive years will be useful for estimating individual external doses from air dose rates, and estimating annual additional exposure doses, if even some of them are applicable to similar life patterns and lifestyles.

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.

Evaluation of Fukushima Daiichi Unit 1 Ex-Vessel Phenomenon Leveraging on Primary Containment Vessel Robotic Inspections

The Great East Japan Earthquake and subsequent tsunami that struck the Fukushima Daiichi Nuclear Power Station gave ground to a set of events that resulted in an unprecedented severe accident occurring simultaneously in multiple reactors of one nuclear power station and significant release of radioactive materials into the environment. Following these events, Tokyo Electric Power Company in cooperation with domestic and international partners has made continuous efforts to clarify in detail the progression of the accident utilizing both analytical tools and robotic inspections of the damaged units. Recently, multiple inspections utilizing submersible remotely operated vehicles were conducted between December 2022 and March 2023, including the first entry into the pedestal area below the damaged reactor pressure vessel of Unit 1. This paper discusses the findings of these inspections in light of the evolving understanding of the accident scenario, leveraging insights gained through experimental and analytical studies on ex-vessel severe accident phenomena. The outcomes of these investigations have yielded new knowledge and highlighted existing gaps in our understanding. The identified knowledge gaps provide direction for future studies, ultimately advancing the level of nuclear safety.

LIBS as diagnostics of analytical chemistry for surface mapping of complex mixed samples simulating debris inside the TEPCO's Fukushima Daiichi Nuclear Power Plant (FDNPS) reactor cores

The Nuclear Energy Agency (NEA) launched the Nuclear Education, Skills and Technology (NEST) Framework to pursue careers in the nuclear field, by exposing researcher working on these topics to international challenging project of real-world issue and by transferring the knowledge and expertise accumulated in the current generation to them through hands-on training.In this framework the 2022 edition of the NEST project offered a training educational period at the Collaborative Laboratories for Advanced Decommissioning (CLADS) located at Tomioka, Futaba District, in the Fukushima prefecture (Japan).Among the research sectors active at CLADS there is the application and development of the LIBS technique as diagnostics of analytical chemistry aiming at characterizing the debris inside the Tokyo Electric Power Company (TEPCO)’s FDNPS reactor cores after the tsunami of March 2011, which destroyed three of the six reactors of the plant. These debris need to be chemically characterized with techniques suitable to be implemented in compact, remote and radiation resistant devices, due to the residual radioactivity of the cores. The present study shows the results in realizing chemical bi-dimensional maps of samples in the form of compressed tablets of mixed oxides, with a complex distribution and concentration of chemicals simulating these debris. The results allowed to create detailed maps of the samples, with spatial resolution down to 0.5 mm and an excellent correspondence between the real spatial distribution of the materials and that reconstructed by LIBS.Moreover, it was found a good correspondence between the nominal concentration of the chemicals and the concentration estimated by using LIBS.This study shows the potentialities of LIBS in the realization of chemical maps on samples of interest for FDNPS, providing multi-elemental images of the samples under analysis.

Statistical evaluation of individual external exposure dose of outdoor worker and ambient dose rate at evacuation ordered zones after the Fukushima Daiichi Nuclear Power Station accident

Following the accident at the Fukushima Daiichi Nuclear Power Station, evacuation orders were issued for the surrounding communities. In order to lift the evacuation order, it is necessary to determine individual external doses in the evacuated areas. The purpose of this study was to determine the quantitative relationship between individual external doses and ambient dose rates per hour as conversion coefficients. More specifically, individual external doses of Tokyo Electric Power Company Holdings employees in difficult-to-return zone were measured broadly over a long period (fiscal year 2020 to fiscal year 2022). To obtain highly accurate estimates, we used not only ambient dose rates based on airborne radiological monitoring data, but also Integrated dose rate map data that had been statistically corrected to correspond to local ambient dose rate gradients on the ground. As a result, the conversion coefficients based on the ambient dose rate map measured by airborne radiological monitoring were 0.42 for the Evacuation-Order Lifted Zones (ELZs), 0.37 for the Special Zones for Reconstruction and Rehabilitation (SZRRs), and 0.47 for the Difficult-to-Return Zones without SZRRs (DRZs). On the other hand, the conversion coefficients based on the Integrated dose rate map which is a highly accurate dose rate map based on statistical analysis of various types of monitoring that have been studied in government projects in recent years, were 0.78 for the ELZs, 0.72 for the SZRRs and 0.82 for the DRZs. Using these conversion coefficients, the individual external dose can be estimated from two representative ambient dose rate maps provided by the government.

Treated water releases from the Fukushima Dai’ichi nuclear power plant: An overview of the decision-making process and governing institutions

In August 2023, the Tokyo Electric Power Company (TEPCO), with permission of the Japanese government, began to release treated water stored on the site of the Fukushima Dai’ichi nuclear power plant into the Pacific Ocean. Given their unprecedented nature in terms of scale and duration, with over one million tons of water to be released over thirty years, the releases have drawn international scholarly attention from marine policy, law, conservation and social sciences, as well as from policy and science-media sectors more widely. The purpose of this communication is therefore to provide an international audience with an outline of the processes through which the decision to release the treated water was made; and of the institutions and policy frameworks that govern the treated water releases from Fukushima Dai’ichi.

Japan Atomic Energy Agency: Contribution to the Decommissioning of the Fukushima Daiichi Nuclear Power Station and the Reconstruction of Fukushima Prefecture at the Naraha Center for Remote Control Technology Development

Naraha Center for Remote Control Technology Development was established for the development and demonstration of remote control equipment and apparatus to promote the decommissioning of the Fukushima Daiichi Nuclear Power Station of Tokyo Electric Power Company Holdings, Inc. The center has been in operation since 2016. The mission of the center is to contribute to the decommissioning of the Fukushima Daiichi Nuclear Power Station and the reconstruction of Fukushima Prefecture. This report describes the center’s full-scale mock-up test facility, component test equipment for the development of remote control equipment and apparatus, and virtual reality systems and their utilization for the realization of the mission.

Prolonged impact of the Fukushima Nuclear Power Plant Accident on health and society

Prolonged impact of the Fukushima Nuclear Power Plant Accident on health and society Naomi Ito, Research Assistant at the Fukushima Medical University, tells us how the 2011 Fukushima Daiichi Nuclear Power Plant Accident impacted and continues to impact local residents. The health effects on local residents following a nuclear power plant accident are diverse, not only because of radiation exposure but also because of changes in lifestyle and social environment. It has also been indicated that various environmental changes that could emerge during the restoration process may affect residents in various ways over a long time. On March 11, 2011, the Great East Japan Earthquake struck Japan with a magnitude of 9.0. Within an hour, a tsunami hit the shore. Three reactors at the Fukushima Daiichi Nuclear Power Plant (FDNPP, operated by Tokyo Electric Power Company) lost power. The reactors could not be cooled, and core meltdowns occurred, which resulted in an explosion due to hydrogen being generated at high temperatures. As a result, radioactive materials were released and scattered northwest from the power plant.

Health and productivity management initiatives to promote worker health and improve the workplace environment at the Fukushima Daiichi nuclear power plant.

Since the Fukushima Daiichi nuclear power plant (FDNPP) accident in 2011, measures have been taken to address occupational health risks, such as heat illness and infectious diseases, and ensure fitness for duty with the Tokyo Electric Power Company and its contractors. However, with the decommissioning operations set to span several decades and an aging workforce, there arose a need for proactive occupational health strategies that not only addressed these risks but also promoted employee health and created a comfortable work environment. With the Japanese government's promotion of health and productivity management (HPM) for corporations, an HPM-based initiative was launched at the FDNPP in 2019. We designed an HPM questionnaire tailored to the unique conditions at the FDNPP for contractors in 2019. Subsequently, we adjusted the questionnaire annually in light of evolving societal contexts and insights derived from contractors' feedback. This initiative also involved the annual recognition of outstanding contractors. These efforts have led to a steady increase in the number of contractors participating in the HPM survey, with respondents' scores continually improving. We also emphasized dissemination of HPM practices from contractors to their subcontractors due to the complex subcontracting structure at FDNPP, and our results showed that more contractors have been extending these efforts to their subcontractors. Our findings suggest that individual contractors are steadily enhancing their HPM efforts. We are committed to continually offering support to advance HPM throughout the FDNPP.

2023 Fukushima Medical University International Symposium on the Fukushima Health Management Survey, "Thinking Together about Health, Life, and our Future in Fukushima".

In response to the release of radioactive materials and evacuation of residents after the Tokyo Electric Power Company's Fukushima Daiichi Nuclear Power Plant accident, caused by the Great East Japan Earthquake, the Fukushima Health Management Survey (FHMS) began in June of 2011. This survey aims to provide long-term follow-up of the physical and mental health of Fukushima residents and to maintain and improve their health for the future. Every year since 2019, Fukushima Medical University (FMU) has organized the FHMS International Symposium to share survey results with people in Fukushima Prefecture and beyond. The fifth annual symposium convened at FMU's Ekimae Campus on Saturday, 4 March 2023, with the theme, "Thinking Together about Health, Life and our Future in Fukushima."

Staff Perceptions of Tsunami Risk on the Fukushima Coast and Their Difference within the Tokyo Electric Power Company Before the Fukushima Accident

Staff Perceptions of Tsunami Risk on the Fukushima Coast and Their Difference within the Tokyo Electric Power Company Before the Fukushima Accident

The Illegality of Relative Subjects Actions in the Fukushima Daiichi Nuclear Disaster

A 9.0-magnitude earthquake and subsequent 14-meter tsunami occurred in March 2011 in the Northeast Pacific Ocean off the coast of Japan. The Fukushima I Nuclear Power Plant located along the coast was attacked by the tsunami and suffered a nuclear leakage accident, which is called the Fukushima Daiichi Nuclear Disaster. The damage caused by the accident not only affected the local area, but also spread to surrounding nations and regions. This study mainly focuses on the actions of the Japanese government and the Tokyo Electric Power Company in the disaster, and uses literature research method. Information related to the Fukushima Daiichi Nuclear Disaster and relevant conventions have been collected and analyzed. By means of searching, categorizing and comparing the research and study of different scholars, institutions and organizations, the paper collated and analyzed the inappropriate and even illegal behaviors of the Relative Subjects mentioned in the case, and came to a conclusion that these behaviors have violated the Convention on Nuclear Safety, the Convention on Early Notification of a Nuclear Accident and the United Nations Convention on the Law of the Sea.

Arrangements for Telephone Consultation on Radiation Health Effects in a Nuclear Emergency in Japan: Lessons Learned from the Nuclear Accident in Fukushima, Japan, 2011

The Japan Atomic Energy Agency (JAEA) established a telephone consultation system at the request of the Ministry of Education, Culture, Sports, Science and Technology in response to residents’ concerns about the radiation health effects following the nuclear accidents at the Fukushima Daiichi Nuclear Power Station of the Tokyo Electric Power Company (TEPCO) in March 2011. Eight toll-free telephone lines were established and employees with knowledge of radiation health effects were assigned for consultation. The JAEA expert response group for telephone inquiries comprised a telephone response team, a question-and-answer team, and a manager. Approximately 35,000 consultations were conducted from March 17, 2011 to September 18, 2012. Japan’s Basic Disaster Prevention Plan was revised following the accident, where one of the JAEA’s roles for nuclear emergency response was to provide telephone consultation on radiation health effects. The JAEA’s system for telephone consultation was improved following this experience. The description of telephone hotlines in the International Atomic Energy Agency’s guide, GSG-14, published in 2020, was discussed for further improvement in the JAEA’s telephone consultation system.

Evaluation of Molten Corium Spreading and Sedimentation Behaviors Within Primary Containment Vessel in Unit 3 of Fukushima Daiichi Nuclear Power Plant Toward the Best Prediction of Fuel Debris Distribution

Accomplishing the retrieval of fuel debris from Fukushima Daiichi Nuclear Power Plant (1F) Unit 3 (1F3) requires an understanding of its distribution. In this study, we performed real-scale corium spreading and sedimentation behavior analyses using Lagrangian moving particle hydrodynamics and large eddy simulation methods. These methods allowed us to calculate the spreading of corium with various shear viscosities under water conditions and to propose the best estimation for the fuel debris distribution in 1F3. To minimize uncertainties arising from unknown boundary conditions, we investigated relevant parameters through literature review. Our analyses showed that highly viscous corium tends to pile up within the pedestal region under strong convective vapor and boiling heat transfer, while low-viscosity corium spreads to the outside of the pedestal regions regardless of cooling efficiency. We identified three cooling modes based on initial shear viscosity and cooling efficiency and predicted the fuel debris distribution in 1F3 by comparing our results to those of the Tokyo Electric Power Company (TEPCO) and Organisation for Economic Co-operation and Development/Nuclear Energy Agency (OECD/NEA) Benchmark Study of the Accident at the Fukushima Daiichi Nuclear Power Station (BSAF) project. The distribution estimation of highly viscous corium derived from oxidic corium is consistent with the three-dimensional reconstructed image by TEPCO and the calculated results by the OECD/NEA BSAF project.

Assessing the variability of tissue-free water tritium and non-exchangeable organically bound tritium in pine needles in Fukushima using atmospheric titrated water vapor

When conducting environmental tritium monitoring at nuclear and fusion facilities, it is important to understand how tritium concentrations vary within the soil-plant-atmosphere continuum. Past measurements of organically bound tritium (OBT) concentrations have been conducted from the standpoint of ascertaining the persistence of tritium in terrestrial vegetation, and it has been reported that OBT concentrations fluctuate depending on the influence of atmospheric sources and meteorological conditions. The present study provides information on the variability of tritium concentrations in vegetation growing close to atmospheric sources of tritiated water (HTO) in Japan. We conducted measurements of tissue-free water tritium (TFWT) and non-exchangeable OBT (NE-OBT) in pine needles collected from locations near the Tokyo Electric Power Company's Fukushima Daiichi Nuclear Power Plant from 2018 to 2021. The results we obtained indicate that TFWT concentrations fluctuate in response to short-term changes in atmospheric HTO vapor concentrations and that NE-OBT concentrations vary primarily in response to the time-averaged TFWT concentration during the pine needle growing season, which is in turn mainly determined by atmospheric HTO vapor concentrations. Although it is difficult to ascertain the time-averaged TFWT concentration during the growing season by measuring plant materials, our results show that the measurement of atmospheric HTO vapor concentrations provides an effective alternative method of doing this. We believe our findings can lead to better understanding of the potential impact on the terrestrial environment associated with the atmospheric discharge of HTO and can contribute to improving the strategy of environmental tritium monitoring.

Preliminary analysis focusing on in-vessel thermal hydraulics in loss-of-heat removal systems in a sodium-cooled fast reactor

Accident scenarios for the safety evaluation of sodium-cooled fast reactors (SFRs) are categorized into two groups: Anticipated Transient Without Scram (ATWS) and Loss-of-Heat Removal System (LOHRS). The latter is subdivided into two scenarios—Loss-of-Heat Sink (LOHS) and Loss-of-Reactor Level (LORL)—depending on the initiating event. With the development of SFRs, research on ATWS has been paid much attention to due to its rapid accident progression, which could lead to significant radioactive release. Conversely, the significance of LOHRS has increased in recent decades due to lessons learned from accidents at the Fukushima Daiichi Nuclear Power Plant of Tokyo Electric Power Company. However, compared with ATWS, finding and evaluation tools for LOHRS have been limited. Hence, code development is initiated to enhance the severe accident analysis code AZORES, which the Nuclear Regulation Authority developed for the safety evaluation of SFR accidents. This enhancement is achieved by coupling AZORES with plant dynamics code ADYTUM in order to deal with more detailed thermal hydraulics behavior in reactor cooling system. The paper describes the coupling methodology, focusing on the thermal–hydraulic model as the first step of code development and its application. The coupling has been confirmed to be well achieved through a preliminary analysis of LOHS, comparing the results of coupled and single AZORES. The comparison of the analysis results between LOHS and LORL by the AZORES coupled with ADYTUM has been conducted to identify the key phenomena in accident progression. The comparison shows that the coolant leak area and the pressure drop at the piping of the reactor cooling system affect accident progression in LOHS. Consequently, the coupled AZORES is capable of predicting in-vessel thermal–hydraulic behavior in LOHRS successfully, reflecting accident conditions and plant design appropriately.

DOIENVRAD: A database of environmental radioactivity at TEPCO’s Fukushima Dai-ichi Nuclear Power Plant Accident and associated bibliography

A database of artificial radioactivity derived from the Tokyo Electric Power Company’s Fukushima Dai-ichi Nuclear Power Plant accident in March 2011 and of related research articles was established. The database was named as DOIENVRAD. We have already published 58 datasets, in which total number of records is 2.5 million. The database site also allows researchers to search the published datasets and retrieve raw data by specifying time, latitude, longitude, altitude/depth, radionuclide name and sample type. Newly 1.8 million records are subjected to retrieval at this moment and all published data together with already published data will be included for retrieval.