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[en] Highlights: •We identify unreliable instrumentation and provide alternative signals. •Proposed the Empirical Parameter Network based on statistically related parameters. •Connectivity determines which parameters are most important from an I&C perspective. •Proposed method was demonstrated through various SBLOCA scenarios. -- Abstract: During the Fukushima Daiichi nuclear accident, the plant operators' ability to observe the status of the power plant using the instrumentation and control (I&C) system was severely hampered by breakdowns in the plant's network, caused by the earthquake and tsunami. Thus it was difficult to obtain essential information for monitoring the internal situation of the power plant. Also, missing and incorrect information on status caused confusion, which then led to an accident. Clearly, it is crucial that I&C systems maintain the ability to monitor the internal state of reactors, even in such an inferior working environment. Herein we propose a method to identify unreliable instrumentation and to provide alternative signals. Our method, called the Empirical Parameter Network (EPN), provides estimates to replace faulty information based on statistically related parameters, and includes visualizations and other tools to enable recognition of various scenarios. The EPN included essential parameters that were selected on the basis of a literature survey, and was based on statistical analysis of an array of simulated post-accident data. The behavior of each parameter was identified and a data visualization technique was developed to intuitively display parameter correlation information. Connectivity analysis to reveal associations was performed based on the data visualization results. By incorporating the concept of connectivity, we were able to determine which parameters were most important from an I&C perspective, allowing further construction of the EPN. This newly constructed EPN will propose an alternative signal when an incorrect input signal is generated, or even when a specific parameter is missing altogether. The proposed method was demonstrated through various scenarios originating from an initial SBLOCA event, which is considered to be one of the greatest contributors to overall severe accident risk. In this research, the relationships between parameters were confirmed based on analysis of connectivity during an accident. Overall, in the damaged network condition, the reliability of the monitoring system can be improved by using the relationships between the parameters. This research can be helpful in managing accidents.
[en] Highlights: • For inspiration to others the special Nordic cooperation pathways in nuclear emergency preparedness are outlined. • Recent Nordic research work under NKS has produced international state-of-the art results on nuclear emergency preparedness. • Cooperation on nuclear emergency preparedness of smallish countries with similar cultural background can be cost-effective. • Internet links are provided from NKS activity discussions to all relevant NKS project reports for cost-free download. - Abstract: Contrary to most areas of Europe, the Nordic countries (Denmark, Finland, Iceland, Norway, Sweden, and the Faroe Islands) have for many years shared a regional research and development program on nuclear reactor safety and emergency preparedness - NKS. In spite of its project results having received great recognition and having been integrated in state-of-the-art emergency preparedness tools over the world, NKS as an organization does not seem well known outside the Nordic countries. Although the Fukushima accident had no health impact at all in Nordic areas, it taught a number of lessons of generic nature with respect to new R&D tasks that could further strengthen and secure future maintenance of the Nordic region's capability to effectively respond to such events. For broader inspiration, this paper briefly introduces the Nordic nuclear emergency preparedness cooperation channels and outlines the related NKS R&D project initiatives launched after the Fukushima accident, many of which should be of general interest also far outside the region. The paper is intended as an introduction to NKS with an invitation to explore its results. All project results are available cost-free on the NKS website.
[en] Highlights: • We examined trends in exchangeable 137Cs in Fukushima forest soils for 6 years. • The proportion of 137Cs in exchangeable form decreased significantly for 2–4 years. • The proportion of exchangeable 137Cs was almost constant in the following years. - Abstract: We investigated the changes in 137Cs exchangeable fraction in the soils of contaminated forest ecosystems until 6 years after the Fukushima radioactive atmospheric deposits. For this investigation, we performed chemical extractions of 137Cs from both organic and mineral soil layer sampled from two forest stands, Japanese cedar (Cryptomeria japonica) and broadleaf deciduous, mainly konara oak (Quercus serrata), which are located 26–27 km inland from the Fukushima Dai-ichi Nuclear Power Plant. The exchangeable 137Cs as a proportion of the total 137Cs inventory was only 10% in the organic layer and 6.1% in the mineral soil layer about 5 months after the accident at the Japanese cedar site. We observed an exponential decrease in the proportion of exchangeable 137Cs in both organic and mineral soil layer samples over the 6-years observation period at both sites. The proportion significantly decreased within 2–4 years after the accident, becoming almost constant (2–4%). These results support the interpretation that contaminated forests have entered a steady-state phase of 137Cs cycling, although we need more integration for an improved vision of the future of Fukushima forests.
[en] Specific activities of 134Cs and 137Cs in surface soil and moss samples were investigated at 12 locations of Jeju Island, Korea. Specific activities of 134Cs and 137Cs in the surface soil vary from less than MDA to 17 Bq/kg and from 12 Bq/kg to 109 Bq/kg, respectively. Specific activities of 134Cs and 137Cs in moss samples lie in the range 6 Bq/kg–39 Bq/kg and 15 Bq/kg–41 Bq/kg, respectively. The activity ratios 134Cs/137Cs in the soil samples are much less than the reference value of about 1.0, but they are close to 1.0 in the moss samples. Average amount of 137Cs added to the surface soil after the Fukushima accident is estimated to be 7.8±1.7 Bq/kg. The depth profile of 137Cs specific activity has a lognormal shape with a peak between 5 cm and 7.5 cm below the ground. For the cored soil sample, 134Cs was detected up to 3 cm below the ground. - Highlights: • 134Cs and 137Cs distributions were investigated in soil and mosses of Jeju Island. • Large areal variation exists in the soil but the variation is small in the mosses. • The ratio 134Cs/137Cs in the soil is much smaller than the reference value of 1.0. • 134Cs/137Cs in the mosses is close to the reference value. • The activity of 137Cs in soil originating from the Fukushima accident was estimated
[en] This report analyses the data of air (ambient) dose rates measured at 164 points in eastern Fukushima during a period of half a year after 10 June 2011. It is found that at some locations the values decreased or increased extraordinarily although on average the overall dose rates decreased significantly faster than the theoretically predicted rate. Among them the nine most extreme points are selected and analysed. It is found that behind these extraordinary behaviours of air dose rates there exists the combination of wind/rain and artificial structures such as sloped pavements. (author)
[en] The PREPARE project that started in February 2013 and will end at the beginning of 2016 aims to close gaps that have been identified in nuclear and radiological preparedness in Europe following the first evaluation of the Fukushima disaster. Among others, the project will address the review of existing operational procedures for dealing with long-lasting releases and cross-border problems in radiation monitoring and food safety and further develop missing functionalities in decision support systems (DSS) ranging from improved source-term estimation and dispersion modelling to the inclusion of hydrological pathways for European water bodies. In addition, a so-called Analytical Platform will be developed exploring the scientific and operational means to improve information collection, information exchange and the evaluation of such types of disasters. The tools developed within the project will be partly integrated into the two DSS ARGOS and RODOS. (authors)
[en] After the Fukushima Daiichi nuclear power plant accident in 2011, Iitate village was placed under an evacuation order because the level of radioactive materials drifting from the nuclear plant to the village was above a government-set level for allowing residents to live in the area. The evacuation advisory for most of the village was lifted on 31 March 2017. For displaced residents deciding whether or not to return to their homes, it is important to correctly understand and estimate the realistic individual external doses they will receive after returning to the village. In this study, with the support of residents of the village, we used a personal dosimeter (D-Shuttle) coupled with a global positioning system device to measure and thus understand realistic individual external doses while the residents were in Iitate village and to project the individual external doses for different administrative districts as of 1 April 2017. The measured individual external doses measured by D-Shuttle for 38 study participants showed that the doses measured during time spent inside the village were higher and more widely distributed than the doses measured during time spent outside the village. The exposure ratio (ER) was defined as the ratio of additional individual external dose measured by D-Shuttle to the additional ambient dose based on an airborne monitoring survey. The medians of the average ERs were 0.13 (min–max 0.06–0.27) for time spent at home and 0.18 (min–max 0.08–0.36) for time spent outdoors. Projected additional annual individual external doses as of 1 April 2017 for different administrative districts in the village were calculated using ERs obtained in this study. Assuming that individuals spent 8 h per day on outdoor activities and 16 h on indoor activities, additional annual individual external doses were estimated to be below 3 mSv using the mean of the average ERs for most districts in the village, and these values were well below the individual external doses estimated using the approach taken by the central government. The results of this study provide valuable information both for understanding realistic radiological situations in the village and for those who want to know their future individual external dose in order to make a decision on whether or not to live in the village. (paper)
[en] Interest in the need for systematic radiology education has increased since the Fukushima Daiichi nuclear disaster. Practice and attitude surveys on radiology education have been previously undertaken and indicate that there is currently limited quantitative knowledge on the use of radiation and radiological consequences. Although maintenance of an education system and measurements of its effects on knowledge levels have been conducted, no novel developments have been made in the methods of measurement. In this study, we measured the effect of the infographics to develop more effective educational materials and lecture methods in radiology education. In addition, we quantitatively evaluated the effects of using infographics on changes in knowledge levels using statistical analysis. (authors)
[en] Highlights: • Improved collection and measurement technology reviewed for legacy aerosol systems. • New capabilities enable the verification responsibilities of aerosol systems in high-level release scenarios. • Electrostatic precipitation improves sample air volume per watt. • Simple MDC analysis shows existing systems could benefit from alternative operations. • Shorter sampling intervals will enable better source location estimates. - Abstract: Pacific Northwest National Laboratory (PNNL) staff developed the Radionuclide Aerosol Sampler Analyzer (RASA) for worldwide aerosol monitoring in the 1990s. Recently, researchers at PNNL and Creare, LLC, have investigated possibilities for how RASA could be improved, based on lessons learned from more than 15 years of continuous operation, including during the Fukushima Daiichi Nuclear Power Plant disaster. Key themes addressed in upgrade possibilities include having a modular approach to additional radionuclide measurements, optimizing the sampling/analyzing times to improve detection location capabilities, and reducing power consumption by using electrostatic collection versus classic filtration collection. These individual efforts have been made in a modular context that might constitute retrofits to the existing RASA, modular components that could improve a manual monitoring approach, or a completely new RASA. Substantial optimization of the detection and location capabilities of an aerosol network is possible and new missions could be addressed by including additional measurements.
[en] Date (da’te) City in Fukushima Prefecture has conducted a population-wide individual dose monitoring program after the Fukushima Daiichi Nuclear Power Plant Accident, which provides a unique and comprehensive data set of the individual doses of citizens. The purpose of this paper, the first in the series, is to establish a method for estimating effective doses based on the available ambient dose rate survey data. We thus examined the relationship between the individual external doses and the corresponding ambient doses assessed from airborne surveys. The results show that the individual doses were about 0.15 times the ambient doses, the coefficient of 0.15 being a factor of 4 smaller than the value employed by the Japanese government, throughout the period of the airborne surveys used. The method obtained in this study could aid in the prediction of individual doses in the early phase of future radiological accidents involving large-scale contamination. (paper)