Tokyo Electric Power Company Research Articles

Final activity report of the “Workshop of Advanced Studies for Steam Flow Measurement”

The "Workshop of Advancement of Steam Flow Measurement" started its activities in April 2017 within the Power and Energy Systems Division of the JSME and finished as planned in March 2022. The industrial sector has a steam demand of 1.12 million TJ/year, which is the second largest energy source after electricity, and steam accounts for about 80% of the heat energy use in the industrial sector and is widely used in large quantities in the main production processes: sterilization, drying, cleaning and distillation. Steam is thus a major heat source in the industrial sector and there is a strong need for flow measurement from the perspective of energy conservation. However, flow measurement of steam is very difficult due to its high temperature and susceptibility to wetness. In addition, there are very few measurement standards. Therefore, the study group has made efforts to clarify the condition of application and accuracy of each measurement method with regard to the flow measurement method of steam. The number of committee members is 30 (chief: Shuichi Umezawa (Tokyo Electric Power Company Holdings, Inc.), vice-chair: Ryo Morita (Central Research Institute of Electric Power Industry), secretary: Tatsuya Funaki (National Institute of Advanced Industrial Science and Technology)), who come from universities, companies, research institutes and others. The frequency of its activities is as follows: it holds study groups once or twice a year, summarizes its results and publishes a report. The predecessor of this study group, the "Workshop of Wet Steam Flow Measurement" (April 2012 - March 2017), also published a report summarizing its overall activities. On the basis of these results, an academic standards development committee has been set up this year and is preparing guidelines for the correction of wet steam flow rate indications from the perspective of thermal energy utilization.

Ensuring Information Disclosure and Environmental Impact on Nanoradioactive Operation of Civil Nuclear Facilities in China

Japan was struck by a massive earthquake that triggered a tsunami in March 2011, which led to a severe nuclear accident at the Fukushima Daiichi Nuclear Power Plant of the Tokyo Electric Power Company. Now, more than 10 years later, it is widely acknowledged that the civil nuclear industry is of great importance in reducing greenhouse gas emissions, improving natural environmental quality, and safeguarding national energy security. Nanomaterials and nanotechnologies, which have gained wide consideration in recent years, have shown a wide variety of application potentials in the future nuclear energy system. Thus, China has been developing its civil nuclear industry throughout the years, despite the nuclear accident in Fukushima, Japan. As a result, China is currently one of the countries with the most nuclear power plants. However, due to the potential radioactive risk, the public has an instinctive fear of civil nuclear development. To alleviate the public’s antinuclear sentiment, the Nuclear Safety Law was formally implemented in 2018, and Measures for Disclosure of Nuclear Safety Information were issued by the Ministry of Ecology and Environment of China in 2020, both stipulating that the public has the right to obtain information about nuclear safety and be involved in related activities. The purpose of such legislation is to eliminate the public’s doubts and phobia about the development of the civil nuclear industry. However, challenges still exist. Although such suggestions have been proposed, such as information disclosure and social involvement should begin as early as the siting of such nuclear facilities, mechanisms to provide sufficient compensation to the public living near nuclear facilities should be established, and these suggestions still have not been applied in the law of China and either not been practiced exactly so far. So, even though all the suggestions have strong feasibility themselves under today’s circumstances in China, it is not easy to judge the effectiveness of these suggestions until they are fully practiced. It is the biggest problem of existing works in this paper. To highlight the serious problems in information disclosure and public involvement in the siting and construction of civil nuclear facilities, several case studies were investigated as the major methodology in this research. Moreover, a legislation study was used to analyze the current content of related legislation and regulations. A qualitative methodology was also adopted to summarize the legal problems surrounding information disclosure and social involvement during the siting and construction of civil nuclear facilities. Information disclosure and public participation still face several obstacles in China, even though laws and regulations guarantee people the right to access available information and take part in pertinent decision‐making. This is particularly true when it comes to the siting and construction of civil nuclear facilities. Thus, in the last several years, several antinuclear incidents have been initiated by the public due to a lack of information and mechanisms to participate. According to the examined cases, information disclosure and public involvement are still not sufficient during the siting of nuclear facilities. A relevant compensation mechanism for people living around nuclear facilities has not been established, and public education on basic nuclear safety is lacking. Therefore, public involvement cannot be completely realized. To ensure information disclosure and public involvement in civil nuclear facilities, this article proposes that information disclosure and social involvement begin as early as the siting of such facilities. Furthermore, operators of nuclear facilities and local governments should establish mechanisms to provide sufficient preventive compensation to the public living near nuclear facilities and attempt to popularize the science of nuclear safety to avoid public misunderstanding.

尤度推定手法を用いた超音波漏洩箇所推定システムに関する基礎研究

In the decommissioning process of the Fukushima Daiichi Nuclear Power Plant of the Tokyo Electric Power Company, Incorporated (TEPCO), it is necessary to investigate the leakage area of coolant and so on. We have focused on ultrasonic measurement as an investigation method to supplement optical measurement methods such as cameras.In this study, we have developed and verified a measurement system using ultrasonic velocity distribution measurement and ultrasonic environmental measurement to measure the velocity distribution in a wide area and to estimate the leakage point in unknown underwater environment, aiming to apply the measurement method to a robot for the investigation in the reactor during the decommissioning work process.

Trend in Cancer Incidence and Mortality in Fukushima From 2008 Through 2015.

BackgroundCancer incidence in Fukushima Prefecture, especially thyroid cancer, has been a public concern, since the Tokyo Electric Power Company Fukushima Daiichi Nuclear Power Plants accident following the Great East Japan Earthquake on March 11, 2011; however, cancer incidence for Fukushima residents before and after the accident based on a population-based cancer registry (PBCR) has not been known worldwide.MethodsWe obtained the corrected-incidence data for invasive cancers newly diagnosed from 2008 through 2015 from the Fukushima Cancer Registry. We checked data quality indicators for PBCRs to confirm comparability. We calculated age-standardized annual incidence and mortality of cancer for all-site, thyroid, and leukemia by calendar year and sex, as we did for Tochigi Prefecture and all of Japan as references for comparison. We applied joinpoint trend analysis to test an apparent trend in incidence and mortality.ResultsThe corrected incidence data from the Fukushima Cancer Registry had sufficient quality comparable to other PBCRs. For the age-standardized annual incidence by sex and cancer type in Fukushima and Tochigi, we did not detect any joinpoint in trend with statistical significance. Cancer incidence gently increased from 2008 through 2015 nationwide. Incidence and mortality of cancer for Fukushima before the accident was very close to that for Tochigi.ConclusionsWe interpreted the incidence statistics of cancer for Fukushima residents from 2008 through 2015. Our results will provide fundamental statistics for subsequent researchers to assess the relationship between the disaster and cancer incidence among Fukushima residents in the long term.

Consequences of marine ecological environment and our preparedness for Fukushima radioactive wastewaterdischarge into the ocean

<p indent="0mm">Ten years after the Fukushima nuclear accident (FNA), Japan announced the planned discharge of over one million tons of Fukushima radioactive wastewater (FRW) into the Pacific Ocean in two years. This decision regarding FRW disposal has aroused worldwide concerns and public fears, which may be exacerbated by reputational damage and the lack of a clear public understanding of the possible adverse impacts of the FRW. As one of the countries surrounding the Pacific Ocean, China is a stakeholder in this decision regarding the FRW disposal. In this study, we compared the FRW source and its associated radionuclide components with the liquid effluent from routine operation of the nuclear power plant and its associated radionuclides. The activity concentrations of 13 radionuclides in the pre- and post-treated FRW by the Advanced Liquid Processing Systems (ALPS) were quantitatively compared with limits for radionuclide concentrations required by Japan law, guidance levels for radionuclides in drinking water provided by the World Health Organization (WHO), and baseline concentrations of radionuclides in surface seawater from the Pacific Ocean before the FNA. Sediment-seawater distribution coefficients and bioconcentration factors are also shown to provide insights into the mobility and biological availability of radionuclides derived from the FRW in the marine environment. Although 62 radionuclides can be recovered from the FRW by ALPS according to a report from the Tokyo Electric Power Company (TEPCO), a large amount of ³H remains in the ALPS-treated FRW. The total amount of ³H in the ALPS-treated FRW was approximately <sc>8.6×10¹⁴ Bq</sc> (by October 31, 2019), with an average concentration of <sc>7.3×10⁵ Bq/L,</sc> higher than the concentration limit <sc>(6×10⁴ Bq/L)</sc> required by Japan law and guidance level <sc>(10⁴ Bq/L)</sc> provided by the WHO. The amount of ³H in the ALPS-treated FRW <sc>(8.6×10¹⁴ Bq</sc> by October 31, 2019) is continually increasing, and is already higher than the amount of ³H (3×10¹⁴<sc>‒7×10¹⁴ Bq)</sc> released into the Pacific Ocean immediately after the FNA. Additionally, other radionuclides (e.g., ¹⁴C, ⁹⁰Sr, ¹²⁹I, etc.) in the ALPS-treated FRW with high bioconcentration factors and high activity-dose conversion factors relative to ³H should also be carefully monitored and evaluated. The measured results provided by the TEPCO indicated that ~70% of the current ALPS-treated FRW should be repurified to reduce concentrations of other radionuclides to meet Japan’s legal requirements. Despite several unresolved factors (e.g., the FRW source terms, discharging plan, hydrodynamic and biogeochemical processes, etc.) simultaneously influencing the fate of FRW in the marine environment, we qualitatively described the hydrodynamically driven passive transport pathway and the biologically driven active transport pathway of the FRW. The transport of the FRW should be comprehensively investigated from the perspective of physical-biogeochemical processes at multiple scales (e.g., large-scale wind-driven circulation, mesoscale eddies, small-scale turbulence) and three-dimensional (e.g., vertical and horizontal vectors) oceans. Key gateways and transport pathways relevant to the FRW entry into the China seas have been suggested to include the Luzon Strait, the outer continental shelf and cross-shelf penetrating fronts in the East China Sea, the Yellow Sea Warm Current, and the Korean Coastal Current. Under specific conditions, the neglected biologically driven active transport pathway may significantly accelerate transport speed for the FRW-derived radionuclides via migratory animals (e.g., Pacific bluefin tuna) and may impose relatively high radiological risk to humans via seafood consumption. Finally, the consequences of marine ecological environment and our preparedness for the FRW release were discussed from the perspectives of total radioactivity, radionuclide components in the FRW, transport pathways of the FRW, and enhancing capacity to meet radiological risk assessment needs. Nuclear power plants located near the coastal seas are gradually developing in China and play a significant role in China’s national strategy of “Carbon Neutrality”. Technical systems of measurement, tracer, and assessment of radionuclides in the marine environments should be given more attention and be continually enhanced in line with the development of nuclear power plants. Several directions including extremely low minimum detection activity for the analytical methods of radionuclides, buoy-based online and real-time measurement technology for marine radioactivity, construction and validation of numerical models for marine radioactivity, key marine biogeochemical processes for radionuclides, radiation dose-effect for marine biotas, radiological assessment models, and remediation technology for radionuclides in marine environments are emphasized as key technologies in nuclear emergency preparedness to protect marine environment security.

Ambient Temperature Sodium Polysulfide Catholyte for Nonaqueous Redox Flow Batteries

Long-duration energy storage (LDES) systems are needed to enable widespread adoption of intermittent energy resources. Redox flow batteries (RFBs) are particularly well-suited for grid-leveling applications because the system’s energy and power densities can be independently scaled. Despite exciting recent progress in both aqueous and nonaqueous systems, a major limitation of RFBs remains their high cost. For LDES applications, developing high energy density electrolytes containing earth abundant active materials is critical to meet targets for installed energy capital costs.Na-based batteries containing sulfur cathodes are attractive for low cost, high energy batteries due to sulfur’s earth abundance and high capacity (e.g., 1,672 mAh/gS for complete reduction to Na2S). Notable examples of S electrodes for reversible Na storage include: (i) molten S (e.g., high temperature Na/S batteries commercialized by NGK Insulators, Ltd. and Tokyo Electric Power Company), (ii) S-based composites containing carbon matrices designed to mitigate dissolution of sodium polysulfides (Na2Sx) in liquid electrolytes, and (iii) RFB electrolytes containing soluble Na2Sx species.This presentation will describe recent work on Na-based biphenyl|polysulfide RFBs and will highlight the effects of soluble vs. insoluble reaction products on reversible capacity and cycling stability. Full cells exhibited stable capacities (up to 200 mAh/gS) with high coulombic efficiency (99.68 ± 0.40%) and negligible capacity fade in both static and flowing cell geometries. For the first time in nonaqueous RFBs, we report the use of 3-electrode galvanostatic AC impedance measurements to identify rate limiting processes in the system. These findings demonstrate that voltage losses are dominated by charge transfer at the cathode, and relevant kinetic parameters (i.e., exchange current density and transfer coefficients) were calculated through a Tafel analysis. In this study, Na+ ß” Al2O3 (BASE) was used as a prototypical membrane, but practical systems require development of low-cost, mechanically robust membranes with high ionic conductivity and minimal crossover. Acknowledgements This research was conducted at Oak Ridge National Laboratory, managed by UT Battelle, LLC, for the U.S. Department of Energy (DOE) and is sponsored by the U.S. Department of Energy through the Energy Storage Program in the Office of Electricity.

IRPA practical guidance for engagement with the public on radiation and risk

The International Radiation Protection Association, IRPA, promotes the worldwide enhancement of professional competence, radiation protection (RP) culture and practice by providing benchmarks of good practice, as well as encouraging the application of the highest standards of professional conduct, skills and knowledge for the benefit of individuals and society. Enhancing public understanding of radiation and risk is highlighted by experiences from past emergencies, including the accident at Tokyo Electric Power Company’s (TEPCO) Fukushima Daiichi Nuclear Power Plant in 2011 and the following post-disaster recovery, as one of the most important challenges, and this challenge is common across almost all public interfaces regarding radiation and risk. To this end IRPA has been continuing a Task Group activity for Public Understanding since 2013. After a series of workshops in various regions of the world, the IRPA draft guidance was developed and issued for consultation of the Associate Societies in 2019. Through these processes, IRPA received a lot of helpful comments and suggestions. IRPA finally published ‘Practical Guidance for Engagement with the Public on Radiation and Risk’ on the IRPA website in October 2020. The objective of the guidance is two-fold. Firstly, it is to enthuse all of us in our profession to become more active public advocates for RP. Secondly, it is to provide information, experiences and techniques to help us to become more effective and comfortable in this challenging task. This paper provides a key summary of the published IRPA guidance.

Research on the Evolution Trend of Energy Enterprise Organization Form

With the development of digital technology, energy enterprises have turned to digital transformation. In this context, the organizational form of energy enterprises will also change. This study put forward the path of energy enterprise organizational reform. Taking EDF, Tokyo Electric Power Company and other companies as examples, the study summarized the factors that influence the choice of energy enterprise organization. Finally, the study pointed out the future evolution direction of energy enterprise organization.

Development of the Multi-Cubic [formula omitted]-ray spectrometer and its performance under intense 137Cs and 60Co radiation fields

The number of nuclear facilities being decommissioned has been increasing worldwide, in particular following the accident of the Tokyo Electric Power Company Holdings’ Fukushima Daiichi Nuclear Power Station in 2011. Large amounts of radioactive wastes and spent nuclear fuels are stored in these facilities. Furthermore, advanced radiation therapies such as proton therapy, ion therapy, and boron neutron capture therapy using charged-particle accelerators have become popular, but charged-particle accelerators generate radiators during operation. In these nuclear and radiation facilities, proper management of radioactive materials is required until the end of the deactivation, cleanup, or disposal. Then, γ-ray spectroscopy techniques have been useful tools because they can obtain significant information on radioisotopes. Besides, space information of radioisotopes is also important, and γ-ray imaging is also required. However, intense radiation fields are located at these facilities, causing γ-ray spectroscopy and imaging difficultly. A γ-ray spectrometer with four segmentations using small-volume CeBr3 scintillators with a dimension of 5×5×5 mm3 was developed. The four scintillators were coupled to a multi-anode photomultiplier tube specific to intense radiation fields by individual supplied voltages to the last three stages. We performed the γ-ray exposure to the spectrometer under 137Cs and60Co radiation fields at the National Institute of Advanced Industrial Science and Technology in Japan. Under the 137Cs radiation field, the relative energy resolution at 1375 mSv/h was 9.2 ± 0.05%, 8.0 ± 0.08%, 8.0 ± 0.03%, and 9.0 ± 0.04% for the four channels, respectively. As the dose rate increased, significant spectral downward shifts were observed for the four channels under the 137Cs and60Co radiation fields because of the space charge effects in the photomultiplier tube. However, the Multi-Cubic sensor could provide the total throughput rate for the four channels of greater than 6 Mcps (Mcps: 106 counts per second), which increases the detection efficiency under intense radiation fields.

Early Emergency Responses of the Japan Atomic Energy Agency against the Fukushima Daiichi Nuclear Power Station Accident in 2011

Background: The Japan Atomic Energy Agency (JAEA) is specified in the Disaster Countermeasures Basic Act as a designated public corporation for dealing with nuclear disasters.Materials and Methods: The Nuclear Emergency Assistance and Training Center (NEAT) was established in 2002 as the activity base providing technical assistance to both national and local governments during nuclear emergencies. The NEAT has a robust structure and utilities and special installations, and it organizes training and exercises.Results and Discussion: Due to an offshore earthquake that caused a devastating tsunami in March 2011, a nuclear accident occurred at the Tokyo Electric Power Company’s Fukushima Daiichi Nuclear Power Station. The NEAT responded by conducting off-site environmental radiation monitoring and contamination screening, dispatching special vehicles, offering telephone consultations, and calculating the dispersion of radioactive materials. An examination of the emergency response activities revealed that the organization was prepared for these types of disasters and was able to plan long-term response.Conclusion: As a designated public corporation, the JAEA technically supports the national government, the Fukushima prefectural government, and the Ibaraki prefectural government, all of which responded to the off-site emergencies resulting from the March 2011 Fukushima Daiichi accident

Environmental and Economic Recovery Post-Fukushima Daiichi Nuclear Disaster: Isotope Characteristics and the Recovery of a Crippled Fisheries Industry

The 2011 Tohoku earthquake and subsequent tsunami had a catastrophic effect on the aquaculture industry of the North-East Japanese coast. Ten years on, this paper examines the environmental and economic impacts of this disaster within the context of the Fukushima nuclear meltdown. Following structural damage to the Tokyo Electric Power Company Fukushima Daiichi plant, fisheries and aquaculture industries were suspended, given the initially high radio caesium output into the coastal water column. Daily radiation testing began on all fisheries products, with tentative industry resuming within the Fukushima prefecture once radiation had dropped below the 50 Bq/kg, as stipulated by the Fukushima Fisheries Association. Routine testing continues biweekly (at least until March 2021). As of May 2016, 73 fish species were passed for consumption. The rapid functional recovery of the fisheries industry has been mediated by two factors, the sedimentation characteristics of the caesium isotopes and deposition of isotopes out to sea in an Easterly direction, given the interaction of oceanic currents. While the aquaculture industry may have recovered and food reduced to safe radiation levels, the disaster continues to exert a domestic and international economic impact given the stigma of Fukushima radiation.

STUDY ON REMOVAL OF CESIUM FROM CONTAMINATED SOIL BY ELECTROPHORESIS USING POTASSIUM ACETATE AS ELECTROLYTE

9 years have passed since a large amount of radioactive materials were diffused by the nuclear accident at the Fukushima Daiichi Nuclear Power Station of Tokyo Electric Power Company. The decontamination works have almost been completed, and some of the contaminated soil whose topsoil was stripped and collected was transported to the intermediate storage and incineration facilities. However, the contaminated soil containing the radioactive cesium stored in the temporary storage place has not decreased significantly. Additionally, the transportation of the intermediate storage and incineration facilities have an agenda from the viewpoint of cost. Therefore, it is needed to investigate the method of decontamination by which the radiation dose of contaminated soil can be reduced below 8000 Bq/kg at the temporary storage place. Considering the decontamination in the actual temporary storage place, electrophoresis is the simple method as a decontamination method, and it is desirable to utilize zeolite with ion-exchange property as an inexpensive adsorbent. Ammonium acetate has been considered to be effective as an electrolyte because it has ammonium ion that has high ion-exchange reaction with cesium ion. However, an efficient decontamination cannot be achieved since the adsorption of cesium ions to zeolite is inhibited by ammonium ions. The purpose of this study is to discuss the efficient removal of cesium by using zeolite as an adsorbent and potassium acetate as an electrolyte through the electrophoresis test. From the test results, it is turned out that potassium acetate is suitable to extract cesium efficiently in electrophoresis.

An iterative application of the Green's function approach to estimate the time variation in 137Cs release to the atmosphere from the Fukushima Daiichi Nuclear Power Station

The Green's function approach, which is an approach to optimize model parameters, was iteratively applied to a large number of pairs of observed and calculated values of surface air concentrations (677 pairs) and ambient dose rates (3279 pairs) to estimate the time variation in 137Cs release rate to the atmosphere from the Tokyo Electric Power Company's Fukushima Daiichi Nuclear Power Station, which was heavily damaged on March 11, 2011. Regarding surface air concentrations, observations suitable for the optimization were selected not to affect the derived release rates due to defects in the modeling framework rather than the release rates. It was found that the release rates of 97 out of a total of 497 segments with a width of 1 h in the target period were effectively optimized and that the modeled levels using the optimized release rates generally agreed well with the observed ones. The derived time variation was reasonable and consistent with that of preexisting works which were derived using another approach and broadly employed to assess the consequences of the Fukushima accident.

“Economizing” TEPCO’s Responsibility for the Fukushima Daiichi Nuclear Power Plant Accident

The purpose of this paper is to show that the responsibility of Tokyo Electric Power Company Holdings, Inc. (TEPCO) was “economized” in the wake of the accident. It is argued that responsibility for the nuclear accident was mainly linked to economic responsibility, and that social and moral responsibility were consequently obscured by the financial accounting that followed the accident. This paper also proposes that the responsibility for the accident should not be limited to TEPCO, but that the responsibility of the nuclear industry and regulatory bodies should be more strongly emphasized in order to prevent such accidents in the future. These conclusions are consistent with some of the literature that emerged following the Fukushima accident. The theoretical framework is derived from sociological studies on quantification and accounting literature on economizing. TEPCO’s accounts, the special business plans of TEPCO and the Nuclear Damage Compensation and Decommissioning Facilitation Corporation, and documentation from the Ministry of Economy, Trade and Industry are the main sources that are consulted in this paper.

Conclusions and Suggestions on Low-Dose and Low-Dose Rate Radiation Risk Estimation Methodology

Background: For radiological protection and control, the International Commission on Radiological Protection (ICRP) provides the nominal risk coefficients related to radiation exposure, which can be extrapolated using the excess relative risk and excess absolute risk obtained from the Life Span Study of atomic bomb survivors in Hiroshima and Nagasaki with the dose and dose-rate effectiveness factor (DDREF). Materials and Methods: Since it is impossible to directly estimate the radiation risk at doses less than approximately 100 mSv only from epidemiological knowledge and data, support from radiation biology is absolutely imperative, and thus, several national and international bodies have advocated the importance of bridging knowledge between biology and epidemiology. Because of the accident at the Tokyo Electric Power Company (TEPCO)’s Fukushima Daiichi Nuclear Power Station in 2011, the exposure of the public to radiation has become a major concern and it was considered that the estimation of radiation risk should be more realistic to cope with the prevailing radiation exposure situation. Results and Discussion: To discuss the issues from wide aspects related to radiological protection, and to realize bridging knowledge between biology and epidemiology, we have established a research group to develop low-dose and low-dose-rate radiation risk estimation methodology, with the permission of the Japan Health Physics Society. Conclusion: The aim of the research group was to clarify the current situation and issues related to the risk estimation of low-dose and low-dose-rate radiation exposure from the viewpoints of different research fields, such as epidemiology, biology, modeling, and dosimetry, to identify a future strategy and roadmap to elucidate a more realistic estimation of risk against low-dose and low-dose-rate radiation exposure.

What Can Radiation Protection Experts Contribute to the Issue of the Treated Water Stored in the Damaged Fukushima Daiichi Nuclear Power Plant?

Decommissioning efforts are underway at the reactor where the accident occurred, namely the damaged Tokyo Electric Power Company (TEPCO) Fukushima Daiichi Nuclear Power Plant (FDNPP). However, a large amount of groundwater flowing into the site has become contaminated with radioactive substances and is stored in tanks on site, which has hampered the decommissioning work. Although the inflow of groundwater has been greatly reduced through measures such as the construction of frost walls, approximately 170 m3 of water treated by the Advanced Liquid Processing System (ALPS) is being stored in tanks, each day. The tanks used to store this treated water are expected to become full by around the summer of 2022. It is not easy to get people to understand the efforts of all concerned parties, and providing clear information to these concerned parties is also a challenge. Questions have also been raised regarding whether other alternatives have been fully explored in the ALPS subcommittee. Some people have commented that the answers to the questions raised regarding the biological effects of tritium transmutation are inadequate. Some suspect that the answers are too detailed and incomprehensible, and that the respondents may be manipulating the public with some malicious intent. In any case, each possible plan presents both advantages and disadvantages, depending on the people who are involved. That makes it an ethical and vexing issue that can sway decisions, as perspectives change. While the environmental release plan is scientifically safe, it may represent a painful alternative. On the other hand, a more careful and imaginative approach to the idea of continued storage in tanks or other forms of storage may reveal some troublesome hidden disadvantages. Under these circumstances, experts must be prepared to answer people's questions in a comprehensive and robust manner.

A framework analyzing system status and human activities: Illustrated using 2011 Fukushima nuclear power plant accident scenarios

Systematically modeling human activities and their interactions with complex systems is important in decision making processes. In order to determine appropriate human activities bringing systems to some desired status, integrated analyses combining both components are necessary. However, this can be difficult due to the complexity of the problems and the lack of adequate data. In this work, a framework capable of analyzing system status and human activities as an integrated set is proposed based upon use of a time-dependent Bayesian Network. The 2011 Fukushima Daiichi nuclear power plant accident scenarios are utilized in this work in order to illustrate the framework. Scenarios presented in this work are developed based upon the authors’ interviews with Tokyo Electric Power Company (TEPCO) staff who were directly engaged in Fukushima accident mitigation. In this work, we focus upon problems that TEPCO staff found challenging during the Fukushima accident. Two types of tasks, mitigation activities during ongoing accidents and preparation tasks before potential accidents, are considered. The capability of the framework for providing system status, based upon rapidly changing human activities, can enable decision-makers to select appropriate mitigation strategies for use during emergencies. The capability of the framework in comparing multiple preparation efforts can enable decision-makers to identify appropriate strategies in order to prepare for similar future situations. Beyond the examples illustrated here, the proposed framework can be applied to broader fields and support corresponding decisions as long as corresponding human activity and system models are available.

Development of a Robot Simulator for Decommissioning Tasks Utilizing Remotely Operated Robots

This paper describes the development of a robot simulator for remote decommissioning tasks using remotely operated robots at the Fukushima Daiichi Nuclear Power Station of the Tokyo Electric Power Company Holdings. The robot simulator was developed to provide a remote operation training environment to ensure operator proficiency. The developed simulator allows for the calculation of physical aspects, such as the hydrodynamics of a remotely operated vehicle and the aerodynamics of an unmanned aerial vehicle. A disturbed camera view presented to an operator can be generated by setting parameters such as transparency, color, distortion, and noise. We implemented a communication failure emulator on the simulator in addition to functionalities for calculating the integral dose and generating the gamma camera image. We discuss the functional requirements and introduce the implemented functionalities. The simulator was built using the developed functions and can be executed integrally.

Application of three-dimensional detailed geometry to simulation of melt progression in an intricate BWR lower head

This study analyzes melt progression with core degradation in the core and lower head of a boiling water reactor using a detailed simulation geometry of an in-house three-dimensional simulation code. Since the Fukushima Daiichi nuclear power plant accident of Tokyo Electric Power Company Holdings (TEPCO) in 2011, the condition of the lower head following melt progression has been a topic of interest worldwide. By taking advantage of the unique characteristics of the three-dimensional simulation code, we focus on achieving a more detailed simulation of the reactor pressure vessel in view of future Fukushima decommissioning processes. Molten corium forms in the core and progresses towards the lower head. When the corium reaches water remaining there, it is fragmented and forms fuel debris on the bottom of lower head. Hence evaluating molten corium breakup with water in the lower head is essential for the coolability of fuel debris and the integrity of the lower head to prevent the release of a large amount of radioactive isotopes. To simulate melt progression together with core degradation effectively, we focused on the development of the detailed simulation geometry comprising the core, the core support plate, and the lower head zones as well as the simplified pedestal of the primary containment vessel. The analysis capabilities due to the detailed simulation geometry were preliminarily evaluated under hypothetical conditions (i) melt progression from the core to the pedestal of primary containment vessel, (ii) failure of the core support plate zone due to molten corium, (iii) water pool behavior in the lower head, (iv) the relocation paths of molten materials via the control rod guide tube/control rod drive housing and instrument guide tube, and (v) mixing behavior of molten corium resulting from different fuel assemblies.

Gamma-ray spectroscopy with a CeBr3 scintillator under intense [formula omitted]-ray fields for nuclear decommissioning

Recently, an increasing number of nuclear facilities have been decommissioned worldwide following the 2011 accident of the Tokyo Electric Power Company Holdings’ Fukushima Daiichi Nuclear Power Station. However, large amounts of radioactive wastes and spent nuclear fuels remain on these facilities, leading to intense radiation fields. During the decommissioning processes, radioactive wastes and spent nuclear fuels have to be retrieved under proper management, and γ-ray spectroscopy supports this process. In this study, a small cubic CeBr3 spectrometer with dimensions of 5 mm × 5 mm × 5 mm was manufactured to perform γ-ray spectroscopy under intense γ-ray fields. Furthermore, thanks to both: (1) a digital process unit with sampling rate of 1 Giga samples per second; and, (2), a photomultiplier assembly featuring individual voltages supplied to the last three stages; the device successfully performed γ-ray spectroscopy up to at dose rates of over 1 Sv/h. The energy resolution (full width at half maximum) at 662 keV ranged from 4.4% at 22 mSv/h to 5.2% at 1407 mSv/h for a 137Cs radiation field. Correspondingly, at 1333 keV, it ranged from 3.1% at 26 mSv/h to 4.2% at 2221 mSv/h for a 60Co radiation field. The energy resolution met the requirements to solve the prominent γ-ray spectral lines of 134Cs, 137Cs, 60Co, and 154Eu. These results suggest that the detector has the potential to realize the γ-ray assessment of 134Cs, 137Cs, 60Co, and 154Eu at dose rates of over 1 Sv/h.