• Nuclear Engineering and Technology
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• 제50권8호
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• pp.1246-1254
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• 2018

The importance of performing Level 3 probabilistic safety assessments (PSA) along with a general interest in assessing multi-unit risk has been sharply increasing after the Fukushima Daiichi nuclear power plant (NPP) accident. However, relatively few studies on multi-unit Level 3 PSA have been performed to date, reflecting limited scenarios of multi-unit accidents with higher priority. The major difficulty to carry out a multi-unit Level 3 PSA lies in the exponentially increasing number of multi-unit accident combinations, as different source terms can be released from each NPP unit; indeed, building consequence models for the astronomical number of accident scenarios is simply impractical. In this study, a new approach has been developed that employs the look-up table method to cover every multi-unit accident scenario. Consequence results for each scenario can be found on the table, established with a practical amount of effort, and can be matched to the frequency of the scenario. Preliminary application to a six-unit NPP site was carried out, where it was found that the difference between full-coverage and cut-off cases could be considerably high and therefore influence the total risk. Additional studies should be performed to fine tune the details and overcome the limitations of the approach.

• Nuclear Engineering and Technology
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• 제55권4호
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• pp.1420-1427
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• 2023

Seismic risk has received increased attention since the 2011 Fukushima accident in Japan. The seismic risk of a nuclear power plant is evaluated via seismic probabilistic safety assessment (PSA), for which several methods are available. Recently, the discrete approach has become widely used. This approximates the seismic risk by discretizing the ground motion level interval into a small number of subintervals with the expectation of providing a conservative result. The present study examines the effect of the number of subintervals upon the results of seismic risk quantification. It is demonstrated that a small number of subintervals may lead to either an underestimation or overestimation of the seismic risk depending on the ground motion level. The present paper also provides a method for finding the boundaries between overestimation and underestimation regions, and illustrates the effect of the number of subintervals upon the seismic risk evaluation with an example. By providing a method for determining the effect of a small number of subintervals upon the results of seismic risk quantification, the present study will assist seismic PSA analysts to determine the appropriate number of subintervals and to better understand seismic risk quantification.

• 무역학회지
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• 제44권4호
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• pp.19-34
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• 2019

This study investigates the WTO dispute over Japanese fishery products originated from Fukushima and another seven prefectures. Being subject to an import ban and additional radioactive test requirements, Japan complained that the Korean government's trade measures are inconsistent with the principles of the Agreement on Sanitary and Phytosanitary Measures. This paper considered the contrasting judicial decisions made by the Panel and Appellate Body and analyzed the debates with respect to their trade-discriminatory effects (Article 2.4), the relevance of appropriate level of protection (Article 5.6) and the precautionary approaches (Article 5.7). Consistent with the final rulings, this paper identifies the need for a broaden understanding of regional conditions and qualitative aspects of protection in risk analysis. Findings also suggest that Korea has diverted its fishery imports from Japan to other countries, while Japan has created export diversion from Korea to other destinations.

• Nuclear Engineering and Technology
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• 제53권3호
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• pp.1013-1019
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• 2021

This paper reviewed the temporal changes in the public opinions on nuclear energy in Korea with a big data analysis of nuclear energy-related articles and their comments posted on the portal site NAVER. All articles that included at least one of "nuclear energy," "nuclear power plant (NPP)," "nuclear power phase-out," or "anti-nuclear" in their titles or main text were extracted from those posted on NAVER in January 2010-December 2019. First, we performed annual word frequency analysis to identify what words had appeared most frequently in the articles. For that period, the most frequent words were "NPP," "nuclear energy," and "energy." In addition, "safety" has remained in the upper ranks since the Fukushima NPP accident. Then, we performed sentiment analysis of the pre-processed articles. The sentiment analysis showed that positive-tone articles have been reported more frequently than negativetone over the entire analysis period. Last, we performed sentiment analysis of the comments on the articles to examine the public's intention regarding nuclear issues. The analysis showed that the number of negative comments to articles each month-irrespective of positive or negative tone-was always larger than that of positive comments over the entire analysis period.

• 한국재난정보학회 논문집
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• 제19권3호
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• pp.582-596
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• 2023

연구목적: 본 연구는 원전사고 발생 시 임시 대피시설의 안전성을 강화할 수 있는 방안을 연구하였다. 연구방법: 본 연구에서는 과거의 체르노빌, 후쿠시마, 쓰리마일섬(TMI) 원전사고에 대한 사례연구를 활용하였다. 연구결과: 현재의 방사선 비상 대응 계획은 소개에 중점을 두고 있으며, 실내대피 개념은 단순히 주민 대피를 지원하는 수단으로 활용되고 있다. 그러나 사례연구를 통해 INES-5 이상의 사고의 경우, 소개보다 실내대피를 장려하는 것이 사상자 최소화에 효과적임을 확인하였다. 더 나은 실내대피를 보장하기 위해 아파트를 임시 대피소로 활용할 것을 권장하며, 아파트가 방사선 방호 기술을 갖추도록 개선사항을 제안한다. 결론: 더 나은 실내대피를 보장하기 위해 아파트를 임시 대피소로 활용할 것을 권장하며, 차폐, 양압, 밀폐기술을 이용해서 아파트의 성능을 보완하고자 한다.

• Nuclear Engineering and Technology
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• 제51권6호
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• pp.1540-1553
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• 2019

A nuclear power plant (NPP) is a highly complex system-of-systems as manifested through its internal systems interdependence. The negative impact of such interdependence was demonstrated through the 2011 Fukushima Daiichi nuclear disaster. As such, there is a critical need for new strategies to overcome the limitations of current risk assessment techniques (e.g. the use of static event and fault tree schemes), particularly through simulation of the nonlinear dynamic feedback mechanisms between the different NPP systems/components. As the first and key step towards developing an integrated NPP dynamic probabilistic risk assessment platform that can account for such feedback mechanisms, the current study adopts a system dynamics simulation approach to model the thermal dynamic processes in: the reactor core; the secondary coolant system; and the pressurized water reactor. The reactor core and secondary coolant system parameters used to develop system dynamics models are based on those of the Palo Verde Nuclear Generating Station. These three system dynamics models are subsequently validated, using results from published work, under different system perturbations including the change in reactivity, the steam valve coefficient, the primary coolant flow, and others. Moving forward, the developed system dynamics models can be integrated with other interacting processes within a NPP to form the basis of a dynamic system-level (systemic) risk assessment tool.

• Journal of Multimedia Information System
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• 제7권2호
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• pp.147-156
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• 2020

The author Nakajima was involved in the field of disaster communications and emergency medical care as guest research scientist at the Fukushima Nuclear Accident Independent Investigation Commission established by the National Diet of Japan and reviewer of the Commission's report, and Kurokawa was the chairman of this Commission. Looking back over a decade, we are on the liability issue of bureaucrats and telecom operators, so it's becoming clear what was hidden at the time. The battery of NTT DoCoMo's mobile phone repeaters had a capacity of only about 24 hours, and communication failures increased after one day. The Government also failed to issue an announcement of "Vent from reactor" under the Telecommunications Act Article No. 129. This mistake lost the opportunity to use the third-party telecommunications (e.g. taxi radios). Furthermore, as a result of LASCOM (telecommunications satellite network for local governments via GEO) and a variety of unexpected communication failures, the evacuation order "Escape!" could not be notified to the general public well. As a result, the general public was exposed to unnecessary radiation exposure. Such bureaucratic slow action in emergencies is common in the response to the 2020 coronavirus.

• 전자공학회논문지
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• 제51권3호
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• pp.10-21
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• 2014

후쿠시마 원전사고는 자연재해에 의한 중대사고 발생 시 전원공급 중단 및 극한 환경으로 인해 발전소 내부 상황을 정확하게 파악하지 못하였고, 대부분의 계측제어시스템이 그 기능을 제대로 발휘하지 못해 비상냉각기능이 상실되어 수소폭발 및 다량의 방사능이 누출된 사고였다. 본 논문에서는 중대사고 발생 시에도 발전소 내부 상황을 감시하고, 적절히 제어할 수 있는 비상대응시스템에 대하여 소개하고, 비상대응시스템에 사용되는 무선통신망의 성능요구사항에 대해서 논의하고, 요구사항을 만족시킬 수 있는 비상통신망의 성능을 마코프 모델을 이용하여 분석하였다.

• 시스템엔지니어링학술지
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• 제8권2호
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• pp.47-55
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• 2012

Tsunami disaster, which ruined Japan Fukushima nuclear power plant sites in 2011 March, has raised not only the perception of that Tsunami and/or large scale flooding possibly surpass the design baselines for industry facilities and plants, but also the necessity to establish recovery system against flooding. This study suggests the framework for flooding and drainage system in compliance with flooding and drainage concept to define and identify requirements, functions, and components of the system with traceable relations. The framework with combination to CMMI engineering process is the base of corresponding high level system design.

• 한국초전도ㆍ저온공학회논문지
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• 제25권3호
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• pp.13-17
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• 2023

Magnetic separation technology for small paramagnetic particles has been desired for the volume reduction of contaminated soil from the Fukushima nuclear power plant accident and for the separation of scale and crud from nuclear power plants. However, the magnetic separation for paramagnetic particles requires a superconducting high gradient magnetic separation system applied, hence expanding the bore diameter of the magnets is necessary for mass processing and the initial and running costs would be enormous. The use of high magnetic fields makes safe onsite operation difficult, and there is an industrial need to increase the magnetic separation efficiency for paramagnetic particles in as low a magnetic field as possible. Therefore, we have been developing a magnetic separation system combined with a selection tube, which can separate small paramagnetic particles in a low magnetic field. In the previous technique we developed, a certain range of particle size was classified, and the classified particles were captured by magnetic separation. In this new approach, the fluid control method has been improved in order to the selectively classify particles of various diameters by using a multi-stage selection tube. The soil classification using a multi-stage selection tube was studied by calculation and experiment, and good results were obtained. In this paper, we report the effectiveness of the multi-stage selection tube was examined.