Fukushima Daiichi Nuclear Plant Accident Research Articles

Concept of accident tolerant fuel in nuclear reactors

The excellent behavior of zirconium alloy under normal operating state as well as significant advantage of neutron economy have resulted in the use of zirconium alloy as the cladding material. However, extensive metal-water reaction in the event of severe accidents and subsequent hydrogen generation can be considered to be a big disadvantage for zirconium alloy. The Fukushima Daiichi Nuclear Plant accident has brought challenges to the nuclear industry and renewed attention about the idea of accident tolerant fuels (ATFs). Concept of ATFs is to mitigate the devastating interaction of steam at high temperature with fuel clad in off-normal condition of the reactor. These materials have higher resistance to core degradation, lower oxidation kinetics and can withstand against high temperature for a longer duration of time. Being in the direct contact with the coolant the accident tolerant fuel cladding plays an important role at high temperature in off-normal conditions. Many studies have been initiated worldwide to find an advanced oxidation-resistant alternative cladding material to enhance fuel performance and safety, specifically under accident conditions. One of the candidate materials for fuel cladding in LWRs is oxidation-resistant iron alloys. The stainless steel technology and the material science have been studied extensively and several new generations of increasingly higher performance steels are now commercially available that may offer significant performance improvements over the relatively simple austenitic steels that were utilized as cladding in some early commercial fission reactors. One study has been performed to find the reactivity impact of SiC and stainless steel as clad material on various parameters. This paper presents the results of a study that has been made to understand the reactor physics implications of using SiC and stainless steel as the cladding material.

The ratio of plant 137Cs to exchangeable 137Cs in soil is a crucial factor in explaining the variation in 137Cs transferability from soil to plant.

To mitigate radioactive cesium from soil to plant, increasing and maintaining the exchangeable potassium (ExK) level during growth is widely accepted after Tokyo Electric Company's Fukushima Dai-ichi Nuclear Plant accident in Japan. This is because the antagonistic relationship between soil solution K and 134Cs + 137Cs (RCs) concentrations changes the transfer factor (TF: designated as the ratio of radioactivity of plant organ to soil) of RCs. As the relationship between ExK and TF depends on the soil types, crop species, and other environmental factors, the required amount of ExK should be set to a safe side. Eleven years after the accident, as the activity of 134Cs was almost negligible, 137Cs became the main RCs in most of the agricultural fields in Fukushima Prefecture. We propose a new indicator, the concentration ratio of plant 137Cs to soil exchangeable 137Cs (Ex137Cs), instead of TF, which showed a better correlation with ExK even among soils with different properties (or mineralogy).

Radiation dose and gene expression analysis of wild boar 10 years after the Fukushima Daiichi Nuclear Plant accident

The Fukushima Daiichi Nuclear Power Plant accident led to contamination with radioactive cesium in an extensive environment in Japan in 2011. We evaluated the concentration of radioactive cesium in the skeletal muscles of 22 wild boars and the expression of IFN-γ, TLR3, and CyclinG1 in the small intestine and compared them with those of wild boar samples collected from Hyogo prefecture. The average 137Cs radioactivity concentration in wild boars in the ex-evacuation zone was 470 Bq/kg. Most of samples still showed radioactivity concentration that exceeded the regulatory limit for foods, but the dose remarkably decreased compared with samples just after the accident. IFN-γ expression was significantly higher in wild boars in the ex-evacuation zone than in samples from Hyogo prefecture. TLR3 expression was also upregulated. CyclinG1 expression also tended to be high. Hence, wild boars might have received some effects of low-dose radiation, and immune cells were activated to some extent. However, pathological examination revealed no inflammatory cell infiltration or pathological damage in the small intestine of wild boars in the ex-evacuation area. Long-term monitoring would be necessary, but we consider that the living body responds appropriately to a stimulus from a contaminated environment.

Radioactive contamination profiles of soil, external and internal exposure to Japanese Black Cattle after Fukushima Daiichi Nuclear Plant Accident

Radioactive contamination profiles of soil, external and internal exposure to Japanese Black Cattle after Fukushima Daiichi Nuclear Plant Accident

Testing of the D-Shuttle personal dosemeter

A new dosimetry system was developed in Japan (Chiyoda Technol Corporation). It has been used for purposes of continuous long-term personal dose monitoring of residents in the area affected by the Fukushima Daiichi nuclear plant accident. The system includes a Si-diode based dosemeter, namely D-Shuttle, a small pocket reader, a laboratory table reader and PC with a complementary software application. After insertion of the dosemeter into the pocket reader, the reader's display shows the dose accumulated during the last day and the total dose. In this way, the dose can be checked by the resident anytime. A more detailed dose reconstruction in time can be done in laboratory. We tested this system, and probed its possible usability for first responders that would operate in emergency radiological events. Most of the results were in correspondence with producer's specifications and reference values, but there were several discrepancies observed.

Study of the thermal stability of studtite by in situ Raman spectroscopy and DFT calculations

The design of a safe spent nuclear fuel repository requires the knowledge of the stability of the secondary phases which precipitate when water reaches the fuel surface. Studtite is recognized as one of the secondary phases that play a key-role in the mobilization of the radionuclides contained in the spent fuel. Thereby, it has been identified as a product formed under oxidation conditions at the surface of the fuel, and recently found as a corrosion product in the Fukushima-Daiichi nuclear plant accident. Thermal stability is one of the properties that should be determined due to the high temperature of the fuel.In this work we report a detailed analysis of the structure and thermal stability of studtite. The structure has been studied both by experimental techniques (SEM, TGA, XRD and Raman spectroscopy) and theoretical DFT electronic structure and spectroscopic calculations. The comparison of the results allows us to perform for the first time the Raman bands assignment of the whole spectrum. The thermal stability of studtite has been analyzed by in situ Raman spectroscopy, with the aim of studying the effect of the heating rate and the presence of water. For this purpose, a new cell has been designed. The results show that studtite is stable under dry conditions only at temperatures below 30°C, in contrast with the higher temperatures published up to date (~130°C). Opposite behaviour has been found when studtite is in contact with water; under these conditions studtite is stable up to 90°C, what is consistent with the encounter of this phase after the Fukushima-Daiichi accident.

Analysis of Plasma Protein Concentrations and Enzyme Activities in Cattle within the Ex-Evacuation Zone of the Fukushima Daiichi Nuclear Plant Accident

The effect of the Fukushima Daiichi Nuclear Power Plant (FNPP) accident on humans and the environment is a global concern. We performed biochemical analyses of plasma from 49 Japanese Black cattle that were euthanized in the ex-evacuation zone set within a 20-km radius of FNPP. Among radionuclides attributable to the FNPP accident, germanium gamma-ray spectrometry detected photopeaks only from 134Cs and 137Cs (radiocesium) commonly in the organs and in soil examined. Radioactivity concentration of radiocesium was the highest in skeletal muscles. Assuming that the animal body was composed of only skeletal muscles, the median of internal dose rate from radiocesium was 12.5 μGy/day (ranging from 1.6 to 33.9 μGy/day). The median of external dose rate calculating from the place the cattle were caught was 18.8 μGy/day (6.0–133.4 μGy/day). The median of internal and external (total) dose rate of the individual cattle was 26.9 μGy/day (9.1–155.1 μGy/day). Plasma levels of malondialdehyde and superoxide dismutase activity were positively and glutathione peroxidase activity was negatively correlated with internal dose rate. Plasma alanine transaminase activity and percent activity of lactate dehydrogenase (LDH)-2, LDH-3 and LDH-4 were positively and LDH-1 was negatively correlated with both internal and total dose rate. These suggest that chronic exposure to low-dose rate of ionizing radiation induces slight stress resulting in modified plasma protein and enzyme levels.

Potential environmental impact of the Fukushima Daiichi nuclear plant accident


 Background and Purpose: The 2011 Fukushima Daiichi nuclear reactor incident in Japan resulted in the release of large quantities of radioactive material into the Pacific Ocean through deposition from the atmosphere and liquid discharges from the nuclear facility. Public misconceptions and the scarcity of radiation monitoring along the west coast of Canada have create doubt within the population regarding the safety of the ocean. A radiation survey along some of Vancouver’s beaches was completed to determine whether radioactivity from Fukushima has reached our local shores. Methods: Radiation surveys were conducted at three different locations; Sunset, Spanish Banks and Jericho Beach in Vancouver, British Columbia. Gamma radiation levels were measured using both the Radeye, GR 135 Plus EXPLORANIUM survey meters. At each beach, 30 samples of water, sand and various different artifacts including algae, stones and logs were each surveying. If the radiation detected exceed 0.05μSv/Hr the identification function of the GR 135 Plus EXPLORANIUM would be used to determine if it was from natural or artificial sources. The radiation levels were compared to the expected normal background levels (between 0.05μSv/Hr- 1.0 μSv/Hr) as well as to observed if there was any sufficient differences between the mediums under investigation. Results: The radiation levels along all three beaches did not exceed normal background levels (between 0.05μSv/Hr- 1.0 μSv/Hr). Furthermore, characteristic radionuclides released from this incident, specifically Cesium 134 and Cesium 134, were not detected. There was no sufficient difference between the radiation levels observed from the sand, water and different artifacts (logs, stones, and algae) Conclusion: It was concluded that the radiation levels along the beaches, Jericho, Spanish Banks and Sunset Beach do not present an additional risk to the public visiting this area as a result of this incident.

Determination of atmospheric radiocesium on filter tapes used at automated SPM monitoring stations for estimation of transport pathways of radionuclides from Fukushima Dai-ichi Nuclear Power Plant

Suspended particulate matters (SPM) collected hourly at that time of Fukushima Dai-ichi Nuclear Plant accident in 2011 on a filter tape at many automated SPM monitoring stations located widely in eastern Japan was analyzed in order to determine atmospheric radiocesium concentration. Precise time series of 137Cs concentrations in wide areas of eastern Japan were revealed. Analysis of radioactivity of SPM collected on filter tapes by automated SPM monitoring stations even at 1–2 years after the accident is concluded to give very valuable information to resolve the matter of radioactive contamination by Fukushima accident.

つくば市の降水に含まれる福島第一原発由来のトリチウム、ヨウ素-129の変遷

つくば市の降水に含まれる福島第一原発由来のトリチウム、ヨウ素-129の変遷

Use of TRACE best estimate code to analyze spent fuel storage pools safety

Nuclear policies have experienced an important change since Fukushima Daiichi nuclear plant accident and the safety of spent fuels has been in the spot issue among all the safety concerns. At many countries, the spent fuel of nuclear power plants is not reprocessed so it has to be stored inside the facilities, normally in pools. As nuclear power plants use best estimate codes to perform safety analysis, it is interesting to assess the capacity of such codes to simulate spent fuel pools behavior. This paper uses TRACE thermal-hydraulic code to simulate steady state and transient conditions of spent fuel pools. The steady state results are compared with plant measurements of Maine Yankee with a good agreement between the calculations and the measurements. The transient simulated is a loss of cooling together with a loss of coolant through the transfer channel. TRACE heat transfer radiation model has been activated using the parameters obtained from COBRA thermal-hydraulic code.

Evaluation of dose from external irradiation for individuals living in areas affected by the Fukushima Daiichi Nuclear Plant accident.

In order to effectively and appropriately manage external radiation doses in the affected areas of Fukushima, it is important to identify when, where and how much exposure occurred. It is also necessary to quantitatively measure external exposure and air dose rates for different activity patterns in individuals living and working in Japanese-style buildings. The authors used a new personal dosemeter (D-shuttle) along with a global positioning system and geographical information system to relate personal dose rate with activity patterns and air dose rate. Hourly individual doses obtained by D-shuttle can provide an effective communication tool for those who want to identify when and how much exposure occurs. Personal monitoring of 26 volunteers showed that personal doses obtained from D-shuttle were ∼30% of cumulative air dose estimated by data from the airborne monitoring survey. This analysis showed that, for most study volunteers, the exposure from staying at home represented about half of the total cumulative dose. This suggests that even though the peak exposure doses may be observed outside of working hours, to develop appropriate countermeasures for external dose reduction, it is thus important to identify the contributions of individuals' time-activities. This study provides a valuable basis for developing a realistic and pragmatic method to estimate external doses of individuals in Fukushima.

Problems with Regional and Community Studies on the Fukushima Daiichi Nuclear Plant Accident and Evacuees

Problems with Regional and Community Studies on the Fukushima Daiichi Nuclear Plant Accident and Evacuees

日本学術会議主催学術フォーラムを終えて

日本学術会議主催学術フォーラムを終えて

Survey of radioactive contamination in Fukushima Naka-dori region, Fukushima, Japan

Due to the Fukushima Daiichi Nuclear Plant Accident, a large area of Tohoku & Kanto regions contaminated with radioactive materials. Kinki University Atomic Energy Research Institute (Kinki Univ. AERI) started researches for the radioactive contamination in Fukushima Naka-dori region from the early April 2011. As the result of the research, some conditions of the contaminations become clear. The first one is that air dose rate depends on the condition of the ground surface. The second one is that some radioisotopes from Fukushima Daiichi NPP can be easily found in Naka-dori region at April 2011, but the radioisotopes decayed and became negligible at the middle of July 2011, except for 134 Cs & 137 Cs. The last one is that the decay of radioactive Cesium at urban area of Naka-dori region is faster than the physical half-life.

Effects of radioactive caesium on bull testes after the Fukushima nuclear plant accident.

We aimed to investigate the effect of chronic radiation exposure associated with the Fukushima Daiichi Nuclear Plant accident on the testis from 2 bulls. Estimated dose of internal exposure in one bull was 0.7–1.2 mGy (134Cs) and 0.4–0.6 mGy (137Cs) and external exposure was 2.0 mGy (134Cs) and 0.8 mGy (137Cs) (196 days). Internal dose in the other was 3.2–6.1 mGy (134Cs) and 1.8–3.4 mGy (137Cs) and external dose was 1.3 mGy (134Cs) and 0.6 mGy (137Cs) (315 days). Sperm morphology and spermatogenesis were within normal ranges. 134, 137Cs radioactivity was detected but Cs was not detectable in the testis by electron probe microanalysis. Thus, adverse radiation-induced effects were not observed in bull testes following chronic exposure to the above levels of radiation for up to 10 months. Since we could analyse a limited number of testes, further investigation on the effects of ionizing radiation on spermatogenesis should be extended to more animals.

Radioactive contamination of the atmosphere of Cairo, Egypt, from the Fukushima Dai-ichi nuclear plant accident

Radioactive contamination in air dust particles of Cairo atmosphere from the Fukushima accident was detected by the gamma-ray spectroscopy technique. Analysis of the spectra obtained by using an High-Purity Germanium detector showed that there were some traces of 131I and 134, 137Cs. Estimate and study of concentration of those radionuclides were done over a period of about 5 months after the accident. Comparison with corresponding results in different countries all over the world has been performed.

Mortality Risk amongst Nursing Home Residents Evacuated after the Fukushima Nuclear Accident: A Retrospective Cohort Study

BackgroundSafety of evacuation is of paramount importance in disaster planning for elderly people; however, little effort has been made to investigate evacuation-related mortality risks. After the Fukushima Daiichi Nuclear Plant accident we conducted a retrospective cohort survival survey of elderly evacuees.MethodsA total of 715 residents admitted to five nursing homes in Minamisoma city, Fukushima Prefecture in the five years before 11th March 2011 joined this retrospective cohort study. Demographic and clinical characteristics were drawn from facility medical records. Evacuation histories were tracked until the end of 2011. The evacuation's impact on mortality was assessed using mortality incidence density and hazard ratios in Cox proportional hazards regression.ResultsOverall relative mortality risk before and after the earthquake was 2.68 (95% CI: 2.04–3.49). There was a substantial variation in mortality risks across the facilities ranging from 0.77 (95% CI: 0.34–1.76) to 2.88 (95% CI: 1.74–4.76). No meaningful influence of evacuation distance on mortality was observed although the first evacuation from the original facility caused significantly higher mortality than subsequent evacuations, with a hazard ratio of 1.94 (95% CI: 1.07–3.49).ConclusionHigh mortality, due to initial evacuation, suggests that evacuation of the elderly was not the best life-saving strategy for the Fukushima nuclear disaster. Careful consideration of the relative risks of radiation exposure and the risks and benefits of evacuation is essential. Facility-specific disaster response strategies, including in-site relief and care, may have a strong influence on survival. Where evacuation is necessary, careful planning and coordination with other nursing homes, evacuation sites and government disaster agencies is essential to reduce the risk of mortality.

Reassessing Food Safety, Risk and Globalization in China and Japan

In recent years, the number of food safety incidents in East Asia has led to increased concerns about threats to food safety in the region. Indeed, following the 2008 melamine scandal in China and the 2011 Fukushima Daiichi nuclear plant accident in Japan, these concerns are now at unprecedented levels. This article presents an overview of research in social and cultural anthropology, sociology and area studies on food safety and food sovereignty in China (excluding Taiwan) and Japan. One research area captures emerging research on consumer education initiatives and environmental networks that provide guidelines to food preparation skills and food choices. A second research area addresses providence and efforts of culinary heritage preservation that are linked to national identity building and revitalization, in particular in economically disadvantaged areas. As anthropologist Sidney Cheung has argued, recent trends in research on food have shifted from an analysis of food as a marker of social status towards environmental and health issues that are not linked to social status and have an impact on all consumers.

Tritium in Japanese precipitation following the March 2011 Fukushima Daiichi Nuclear Plant accident

Tritium concentrations in Japanese precipitation samples collected after the March 2011 accident at the Fukushima Dai-ichi Nuclear Power Plant (FNPP1) were measured. Values exceeding the pre-accident background were detected at three out of seven localities (Tsukuba, Kashiwa and Hongo) southwest of the FNPP1 at distances varying between 170 and 220km from the source. The highest tritium content was found in the first rainfall in Tsukuba after the accident; however concentrations were 500 times less than the regulatory limit for tritium in drinking water. Tritium concentrations decreased steadily and rapidly with time, becoming indistinguishable from the pre-accident values within five weeks. The atmospheric tritium activities in the vicinity of the FNPP1 during the earliest stage of the accident was estimated to be 1.5×103Bq/m3, which is potentially capable of producing rainwater exceeding the regulatory limit, but only in the immediate vicinity of the source.