Nuclear Power Plant Accident Research Articles

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.

Thirty-year simulation of environmental fate of 137Cs in the Abukuma River basin considering the characteristics of 137Cs behavior in land uses

The Fukushima Daiichi Nuclear Power Plant accident caused a radioactive contamination of deposited radionuclides, including 137Cs, on the land surface. Cesium-137 deposited on the land surface was strongly adsorbed on soil particles and was then washed off through soil erosion. Trends of temporal variation of 137Cs wash-off varied greatly depending on land use. Therefore, it is important to reflect the characteristics of 137Cs migration processes in each land use to clarify the long-term fate of 137Cs. In this study, a 30-year simulation of environmental fate of 137Cs was conducted using a distributed radiocesium prediction model, taking into account the characteristics of the 137Cs behavior in each land use. Overall, in the Abukuma River basin, the 137Cs transported into the ocean for 30 years was estimated to correspond to 4.6 % of the initial deposition in the basin, and the effective half-life of 137Cs deposited in the basin was estimated to be 3.7 years shorter (by 11.6 %) than its physical half-life. These results suggested that 137Cs deposited from the accident could still remain for decades. Based on the analysis of the 137Cs behavior in land use, in 2011, the contribution of 137Cs export to the ocean from urban lands was estimated to correspond to 70 % of the total 137Cs export. Meanwhile, from 2012 to 2040, the contribution of 137Cs export from agricultural lands was estimated to correspond to 75 % of the total 137Cs export. The reduction ratios excluding radioactive decay of 137Cs remained in areas with and without human activities for 30 years after the accident, defined as the ratios of the total outflow to the initial deposition, were estimated to be 11.5 %–17.7 % and 0.4 %–1.4 %, respectively. These results suggested that human activities enhance the reduction of 137Cs remaining in land in the past and future.

Impact of the Fukushima Accident on 3H and 14C Environmental Levels: A Review of Ten Years of Investigation

The investigation of the impact of the Fukushima accident is still going on although more than ten years have passed since the disaster. The main goal of this paper was to summarize the results of tritium and radiocarbon determinations in different environmental samples, possibly connected with the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. A document containing compiled data may serve as a solid basis for further research in the selected fields. To accomplish such effort, we went through dozens of relevant published papers, reporting 3H and 14C activity concentrations in precipitations, groundwater, seawater, river systems, tree rings, and, in some more extraordinary samples, such as herbaceous plants or debris from the damaged reactor buildings. As the referenced results would not be obtainable without adequate analytical techniques, the most common methods for routine measurement of tritium and radiocarbon concentrations are discussed as well. We believe that the correct identification of the affected environmental compartments could help quantify the released 3H and 14C activities and track their following fate, which could be especially important for plans to discharge contaminated water from the FDNPP in the upcoming years.

Current status and issues of Local Vitalization Cooperators in 12 municipalities affected by Fukushima nuclear power plant accident

本研究の目的は、原子力被災12市町村における地域おこし協力隊の現状と課題を明らかにすることである。我々は、原子力被災12市町村とそこで活動する地域おこし協力隊を対象としたアンケート調査を行った。その結果を基に原子力被災12市町村は生活環境を改善すること、学びの機会を地域おこし協力隊へ提供すること、起業・継業と住宅に関する支援をすることが必要であることを指摘した。

A study on the actual situation and issues of agricultural corporations in 12 municipalities affected by Fukushima nuclear power plant accident

本研究は、原子力被災12市町村における農業法人の実態と今後の課題を明らかにすることを目的とするものである。原子力被災12市町村の農業法人と自治体を対象にして実施したアンケート調査の結果によると、原子力被災12市町村の多くの農業法人と自治体は、特に人材や人員の確保・育成を課題であると認識している。以上のことを踏まえ、農業法人は正社員・正職員を通年雇用することができる環境づくりを進める必要があること、経営状況の改善をする必要があること、自治体は地域おこし協力隊の制度の活用を検討する必要があることを指摘した。

Relationship between radiation knowledge and radiation effect anxiety on the next generation: An analysis of a questionnaire survey disseminated to residents in Fukushima Prefecture

Objectives Since the Fukushima Daiichi Nuclear Power Plant accident caused by the Great East Japan Earthquake, many people in Fukushima Prefecture have been concerned about the effects of radiation on their offspring. Although this fear should be relieved since no epidemiological study has shown evidential cases, situations wherein some people misunderstood the existence of evidence have been independently reported. Therefore, in this study, we examined the relationship between radiation knowledge and anxiety about radiation-based genetic effects using a survey mailed to residents in Fukushima Prefecture.Methods In August 2016, we attempted to contact 2,000 people aged 20 to 79 years in Fukushima Prefecture through a survey distributed by mail inquiring about residents' health. We received 861 responses. Respondents selected their level of concern about radiation effects on the next generation on a four-point scale and answered five knowledge questions about radiation effects and protection. Responses were "correct," "incorrect," or "not sure." After adjusting according to residential area, family configuration, age, sex, academic background, media used, and trusted information source, we conducted multiple regression analyses to investigate the relationship between the level of concern and answers to the knowledge questions.Results People who answered the knowledge questions more correctly had lower levels of anxiety. The number of "not sure" responses was unrelated to anxiety level. The results indicated that correct answers to questions related to radiation residuals in the body and genetic effects were negatively associated with anxiety. Incorrect answers to the question about genetic effects and another related to cell repair systems were positively associated with anxiety. Moreover, while a correct answer to another question related to the linear threshold model had a positive association, the association was insignificant. Further, any response related to radiation reference values in foods showed no association.Conclusion Based on these results, we observed an association between the number of respondents with a correct knowledge of radiation and the degree of anxiety about radiation effects on the next generation. However, this relationship and its strength varied depending on the specific knowledge content. As a limitation of this study, the study could not establish any causality. Further studies, such as prospective interventional studies, should be conducted.

Experimental research on aerosol scrubbing characteristics under steam-air mixture submerged jet condition

The occurrence of severe accidents in nuclear power plants may lead to the leakage of radioactive aerosol. And the scrubbing efficiency of aerosol contained in the air-steam mixture submerged jet is important for assessing the radioactivity in the containment during a severe accident. Several experiments were carried out to analyze the effect of inlet pressure, aerosol diameter, submergence, and steam fraction on the scrubbing efficiency of aerosol in the jet regime. Then, the scrubbing effects of steam and different flow regimes under submerged jet conditions were investigated by comparing the experimental results. The scrubbing efficiency increased with the increase of the aerosol diameter in the air jet regime while the most penetrating region of the aerosol in the steam-air mixture jet regime is 0.2–0.4 μm. When the gas flow characteristic is subcritical flow, as the inlet pressure increases, the scrubbing efficiency increases rapidly. When the critical flow is reached, the inertial effect was the dominant factor in aerosol scrubbing due to the sufficient gas velocity, the scrubbing efficiency under different steam fractions is close to 100%. The scrubbing efficiency increases with the increase of the steam fraction, which may be caused by the increase of the temperature gradient field under subcritical flow conditions. Additionally, the increase the submergence can increase the residence time and improve the scrubbing efficiency. However, due to the decrease of the gas velocity during the gas floating, the scrubbing efficiency in the flow region of the same height is gradually decreasing.

Numerical Evaluation of Coolability Limits of External Reactor Vessel Cooling Using an Improved Thermal-Hydraulic System Analysis Code

The external reactor vessel cooling provides a means to stabilize the molten core inside the reactor vessel during the severe accident in nuclear power plants. For a credible evaluation of the chances of success of in-vessel melt retention, one requires high-fidelity predictions on the natural circulation flow around the reactor vessel and, in particular, the corresponding critical heat flux (CHF) on a hemispherical lower head. In this study, the coolability limit of external reactor vessel cooling in the Korean APR1400 reactor was investigated numerically by improving a thermal-hydraulic system analysis code, MARS-KS1.5. Since such system analysis codes did not incorporate a CHF model for a downward-facing hemisphere, three CHF correlations were newly implemented in the MARS-KS code, two of them taking into account the effect of the mass flux. A transient analysis on the CHF and surface heat flux on the lower head was carried out while the surrounding cooling water was heated to create the two-phase natural circulation flow. The heat transfer mode on the heated surface was used as a measure of evaluating the success of the strategy, and the simulation results were compared with those obtained via the default CHF model in the code. The sensitivity analysis on the heat load from the core melt was also performed.

Pretest analysis of a prestressed concrete containment 1:3.2 scale model under thermal-pressure coupling conditions

In nuclear power plant (NPP) accidents, the containment is subject to high temperatures and high internal pressures, which may further trigger serious chain accidents such as core meltdown and hydrogen explosion, resulting in a significantly higher accident level. Therefore, studying the mechanical performance of a containment under high temperature and high internal pressure is relevant to the safety of NPPs. Based on similarity principles, the 1:3.2 scale model of a prestressed concrete containment vessel (PCCV) of a NPP was designed. The loading method, which considers the thermal-pressure coupling conditions, was used. The mechanical response of the PCCV was investigated with a simultaneous increase in internal pressure and temperature, and the failure mechanism of the PCCV under thermal-pressure coupling conditions was revealed.

Development of a Passive Reactor Shutdown Device to Prevent Core Disruptive Accidents in Fast Reactors: A Preliminary Study

AbstractFollowing the Fukushima Nuclear Power Plant accident in 2011, it has become increasingly important for reactor safety designs to consider measures that can prevent the occurrence of severe accidents. This report proposes a novel subassembly-type passive reactor shutdown device that expands the diversity and robustness of core disruptive accident (CDA) prevention strategies for sodium-cooled fast reactors. The developed device contains pins with a fuel material that is in the solid state during normal operation but melts into a liquid when the temperature exceeds a certain value (i.e., during a potential accident). When an unprotected loss of flow (ULOF) or unprotected transient overpower (UTOP) accident occurs, the device can passively provide significant negative reactivity by rapidly transferring liquefied device fuel into the lower plenum region of the pins via gravitation alone. The reactors containing some of the proposed devices in place of original fuel subassemblies become subcritical before the driver fuels are damaged, even if ULOF or UTOP transient events occur. The present study evaluates candidate materials for device fuels (e.g., metallic alloy, chloride), optimal device pin structures for liquefied fuel relocation, and nuclear and thermal-hydraulic characteristics of the device-loaded core under accident conditions to demonstrate the engineering applicability of the proposed device. This report discusses preliminary results regarding the nuclear requirements for inducing negative reactivity to achieve reactor shutdown under the expected device conditions during an accident.

Deprivation of Furusato: The damage faced by evacuees after the Fukushima nuclear power plant accident

AbstractThis paper considers the damage caused by the Great East Japan Earthquake and the meaning of the Fukushima Nuclear Power Plant accident, and reflects on the evacuees' experiences over past 12 years. During this time, several lawsuits demanding the clarification of responsibility for the accident and compensation for damages have been filed against TEPCO (Tokyo Electric Power Company) and the Japanese Government. The “loss and transformation of hometowns (furusato in Japanese)” has become one of the key issues in these lawsuits. While the casees were being litigated, the mandated “evacuation designated zones” were gradually lifted. Even in the “Difficult‐to‐Return Areas” where annual integrated doses of radioactive substances are over 50 mSv and evacuation orders are still in effect, efforts are being made to lift the evacuation orders. Because they were forced to leave their places of residence, evacuees have claimed, “we lost oue furusato [hometown].” However, because they are able to return after evacuation orders are lifted, both TEPCO and the Japanese Government have insisted that “their furusato has not been lost” and “they cannot claim compensation for furusato damages.” In this paper, I call the irreversible and absolute damage caused by the nuclear power plant accident “the deprivation of furusato.” I look at furusato from three aspects: the relationship between people and nature, the connection between people, and notions of persistence and sustainability. Then, I discuss what kind of reconstruction is being promoted to respond to the deprivation of furusato and for whom.

Historical meaning of post‐Fukushima social movements: Crisis in hegemony in postwar Japan and prefigurative politics in the 2010s

AbstractSince the Great East Japan Earthquake in March 2011 and the nuclear power plant accident, a number of movements have emerged in Japanese society, including the anti‐nuclear power movement and others with a variety of agendas. The social movements of the 2010s in Japan have expanded along with the spread of social networking services and have brought together a new class of people who are different from those of the established movements. This article will compare and examine the social movements of the 2010s with those of the past, as well as the function they played in the social structure. In the early 2020s, a structural crisis in the political and economic foundations of postwar Japan has become apparent. The Japanese social movements of the 2010s were movements that pressed for the transformation of the old social system as well as the transformation of the old anti‐system movements. Thus, this movement had the distinction of prefiguring a fundamental shift in the confrontational frame of reference between conservatism and progressivism that had shaped postwar Japan. This article will discuss the historical significance of the Japanese social movements of the 2010s in light of the structural factors behind the decline of the social base of both conservative and progressive forces.

Modeling the Diffusion of Radioactive Materials into the East Sea of Korea: Analysis of Hypothetical Nuclear Power Plant Accident Scenarios and Long-Term Marine Ecosystem Impacts

Min, B.I.; Suh, K.-S.; Park, K.; Kim, J.Y.; Choi, Y., and Kim, S., 2023. Modeling the diffusion of radioactive materials into the East Sea of Korea: Analysis of hypothetical nuclear power plant accident scenarios and long-term marine ecosystem impacts. Journal of Coastal Research, 39(2), 394–400. Charlotte (North Carolina), ISSN 0749-0208. The East Sea is surrounded by South Korea, North Korea, Japan, China, and Russia and is connected to the Northwest Pacific Ocean through three narrow straits. In the East Sea, there are 18 nuclear power plants installed along the coasts of South Korea alone. This study evaluated the long-term diffusion of radioactive materials in the East Sea using a compartment model and described the effect on a marine food chain model. A hypothetical scenario in which soil near the power plant is contaminated and flows into rivers and seas due to rainfall was numerically tested. It took about 2 minutes to calculate the intake dose for 10 years, and there was no significant difference compared to the detailed model.

Development of a Floating Radiation Measurement System for Underwater Readings in the East Sea of Korea

Joung, S.; Ji, Y.-y., and Choi, Y., 2023. Development of a floating radiation measurement system for underwater readings in the East Sea of Korea. Journal of Coastal Research, 39(2), 384–393. Charlotte (North Carolina), ISSN 0749-0208. Following the Fukushima nuclear power plant accident and subsequent discharge of contaminated water, the need for marine radioactivity monitoring has emerged. Currently, various underwater radiation monitoring systems are being developed and utilized for monitoring radioactive contamination of seawater. In this study, a floating on-site radiation monitoring system that can measure the radiation energy spectrum of a water environment in the field in real time was designed and fabricated with the aim to reduce the effect of background radiation on the system, which is a problem for land-based measurement technology. This study performed computational simulations to derive the ambient dose rate conversion factor and efficiency of the developed floating on-site radioactivity analysis system, named MARK-U3. The system was tested in the laboratory and in the field in both freshwater and saltwater environments. From the experimental results, the MARK-U3 can perform precise radioactivity analysis without the need for a thick shield, and by strengthening mobility, it can operate continuously.

JRODOS customization for Pakistan and assessment of the consequences of a hypothetical nuclear accident

Since the Chernobyl disaster in 1986, decision support systems and modelling tools have been utilized in response to nuclear and radiological emergencies. The java-based real-time online decision support system (JRODOS) is a decision support tool that can be utilised in response to an emergency in managing off-site radiological consequences. This article documents the customization and use of JRODOS for Pakistan. JRODOS was tailored to the local Pakistan conditions, and a case study of a theoretical nuclear power plant accident was used to assess JRODOS’s feasibility as a decision support tool. A worst-case probabilistic accident scenario was used to identify zones and areas where urgent protective actions, early protective actions and food restriction and other response actions could be required. The areas and distances identified for the implementation of protective and response actions for such a hypothetical accident were found to be in agreement with the emergency planning zones and distances suggested by the International Atomic Energy Agency (IAEA). Additionally, the implications of meteorological and source term input parameters on predicting the radiation doses to members of the public were investigated. It was identified that the output of such tools strongly depends on the availability and accuracy of the input parameters, such as radioactive release and meteorological data. Limitations and uncertainties associated with these tools need to be considered in deciding on protective and other response actions in response to a nuclear accident. As established by the IAEA, protective and other response actions need to be applied on a graded approach, taking into account the protection strategy and uncertainties and limitations in the available information and criteria, based on the conditions at the facility and off-site.

Comparison of quality of life between elderly and non-elderly adult residents in Okuma town, Japan, in a post-disaster setting.

With the growing elderly population who are susceptible to poor health, improvement of their quality of life is essential. In the post-disaster setting of the 2011 Fukushima Dai-ichi nuclear power plant (FDNPP) accident, affected municipalities such as Okuma town commenced their recovery processes and lifted evacuation orders in 2019. This study examines the differences in self-reported mental and physical health status, social functioning, risk perception, and intention to return between elderly (age ≥65 years) and non-elderly (age 20-64 years) residents. Questionnaires were distributed to current residents and evacuees of Okuma. Results revealed that the elderly had a 1.4 times higher odds ratio (95%CI 1.0-1.8, p = 0.034) for having anxiety regarding radiation-related health effects on future generations and a 1.3 times higher odds ratio (95%CI 1.1-1.5, p = 0.001) for wanting to know about the release of FDNPP-treated water into the environment than the younger group. Elderly residents also demonstrated a 2.2 times higher odds ratio for reporting poor physical health than younger residents. Clearing misconceptions and disseminating coherent information will reduce risk perception among this group. Further in-depth research regarding the disposal of FDNPP-treated water and its perceived risks is required. Health promotion through the encouragement of social participation, improvement of surroundings to facilitate healthy behaviors, and enhanced access to health services will improve the quality of life of elderly Okuma residents.

Model behavior regarding in- and below-cloud 137Cs wet scavenging following the Fukushima accident using 1-km-resolution meteorological field data

Wet deposition remains an important source of uncertainty in modeling of the atmospheric transport of 137Cs following the Fukushima Daiichi Nuclear Power Plant accident. Its behavior is often difficult to investigate owing to the limited resolution of meteorological field data and inconsistent model implementations. This study investigated the detailed behavior of 25 combinations of in- and below-cloud wet scavenging models using high-resolution (1 km × 1 km) meteorological input. These combinations were all implemented in the Weather Research and Forecasting-Chemistry model, thereby enabling consistent evaluation. The 1-km-resolution simulations were compared with simulations obtained previously using 3-km-resolution meteorological field data. Results revealed that rainfall of <1 mm/h is critical for simulation accuracy. The 1-km results revealed better representation of rainfall than that revealed by the 3-km results, but with spatiotemporal variability in accuracy. Owing to their sensitivity to rainfall, single-parameter wet deposition models showed improvements in performance in the 1-km simulations relative to that in the 3-km simulations. The multiparameter models showed more robust performance in terms of both simulations, and the Roselle–Mircea model presented the best performance among the 25 models considered. Wind transport showed substantial influence on the removal of atmospheric 137Cs, and it was nonnegligible even during periods in which wet deposition was dominant. The 1-km-resolution simulations effectively reproduced local-scale 137Cs concentrations but with deviations in timing, mainly because of biased wind direction. These findings indicate the necessity for a refined wind and dispersion model for local-scale simulation of 137Cs concentration.

Potassium buffering characteristics and detection of soils with challenges in evaluating radiocesium uptake risk of crops by exchangeable potassium

ABSTRACT In surrounding areas influenced by the Fukushima Dai-ichi Nuclear Power Plant accident, the radiocesium uptake by crops was evaluated based on soil exchangeable K. As risk evaluation does not function effectively in several fields, K buffering was characterized using quantity/intensity (Q/I) relationship analysis to evaluate the availability of exchangeable K. The results of the analysis clearly explain the difficulty in the risk evaluation: i) difficulty in increasing exchangeable K, owing to retention as non-exchangeable K by vermiculite; ii) difficulty in retaining exchangeable K due to low K buffering capacity, reflecting the lack of K-selective clay minerals; and iii) difficulty in increasing soil solution K intensity due to high K buffering capacity, reflecting the abundance of K-selective clay minerals. Among the parameters calculated from the Q/I relationship analysis, β values, corresponding to the retention rate of loaded K to the soil, for total K (βt), exchangeable K (βe), and non-exchangeable K (βn) would be useful as simple indicators of soils with a predicament in the risk evaluation of radiocesium uptake by crops through exchangeable K. These soils showed distinctively low βt values (0.18 or lower), high βe value (0.37 or higher), or high βn/βt ratio (0.53 or higher).

Subsurface dispersion path and travel time of radiocesium from Fukushima by Mode Water

The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident on March 11, 2011 resulted in the release of immense amounts of radioactive materials into the ocean. However, the dispersion of radioactive materials in the subsurface has not yet been clarified due to the spatiotemporal limitation of observations. Thus, herein, a tracer experiment was implemented using a three-dimensional numerical model to estimate the dispersion path of 137Cs released directly from the FDNPP and its travel time in the subsurface of the North Pacific Ocean from 2011 to 2020. The results show that the subsurface 137Cs spreads by two mode waters, namely, Sub-Tropical Mode Water (STMW) and Central Mode Water (CMW). Subsurface 137Cs primarily spreads clockwise in the sub-tropical region, while a portion driven by STMW is dispersed southward. The clockwise dispersion path of 137Cs released into the ocean by STMW is relatively shallower and inward than that by CMW. The 137Cs that was spread clockwise reached the east of Taiwan and the Philippines via STMW and CMW nine years after the accident, respectively. The model described in this study is applicable for estimating the water path and travel time of tritium water planned to be discharged from Fukushima.

Modelling and simulating of premixed layer in stratified fuel coolant configuration

A hypothetical severe accident in a nuclear power plant can lead to significant core damage, including melting of the core. The interaction between the molten core and the coolant water is known as a fuel–coolant interaction. One of the consequences can be a rapid transfer of a significant part of the molten corium thermal energy to the coolant in a time scale smaller than the characteristic time of the pressure relief of the created and expanding vapour. Such a phenomenon is known as a vapour explosion. Given possibly a large amount of thermal energy, initially stored in the liquid corium melt at about 3000 K, and pressure peaks of the order of 100 MPa, vapour explosion can be a credible threat to the structures, systems and components inside the reactor containment. It can also threaten the integrity of the reactor containment itself, which would lead to the release of radioactive material into the environment and threaten the general public safety. In analyses of severe accidents in nuclear power plants, a fuel–coolant interaction was mostly addressed in a geometry of a melt jet poured into a coolant pool. Based on some experimental and analytical work from the past a geometry with a continuous layer of melt under a layer of water, called stratified configuration, was believed to be incapable of producing energetic fuel–coolant interaction of sufficient magnitude to likely fail the containment. However, the results from recent experiments performed at the PULiMS and SES facilities (KTH, Sweden) with corium simulants materials contradict this hypothesis. In some of the tests, a premixing layer of ejected melt drops in water was clearly visible and was followed by strong spontaneous vapour explosions.The purpose of our research is to improve the knowledge, understanding and modelling of the fuel–coolant interaction and vapour explosion in stratified configuration. Based on the past experimental and analytical research, mechanisms for the premixed layer formation are identified and a model for the melt-coolant premixed layer formation in stratified configuration is presented. The analyses on the PULiMS and SES experimental results demonstrate the model’s capability to describe the premixed layer formation.