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[en] This paper gives an overview of the serious nuclear reactor accidents that have occurred in the world to date, and then explains the three-mile island (TMI) nuclear power plant Unit 2 accident and the Chernobyl nuclear power plant Unit 4 accident among commercial nuclear reactor accidents. For each accident, it describes an overview of the accident, stakeholders' involvement, and the current state. It also describes, for TMI Unit 2, the decommissioning and disposal of treated water (tritium water) after the accident, and for Chernobyl Unit 4, the shelter and new safe confinement facility. One common characteristic of the TMI and Chernobyl accidents is that the government had set up a public specialized agency to interact with the citizens. In the case of the U.S., the Nuclear Regulatory Commission (NRC) set up an 'advisory panel for decontamination of TMI-2', and the members were also appointed from local residents. In the case of Ukraine, the State Nuclear Regulatory Inspectorate of Ukraine (SNRIU) set up a 'Public Council' to discuss the decommissioning of Chernobyl from the perspective of citizens, and its activities are still ongoing. It is probable that both countries have placed particular emphasis on dialogue with citizens in the measures for the decontamination of the accident reactors. It is considered to be significant to grasp the decommissioning measures and the method of dialogue with citizens after nuclear accidents that occurred in foreign countries. (A.O.)
[en] As of August 2018, nuclear power generation had been introduced in 31 countries, and there are 450 nuclear reactors for power generation. The countries with large capacity of nuclear power generation are the U.S., France, China, and Japan, but in Japan, only 9 units have been restarted among 39 units. With 298 nuclear reactors operating around the world for over 30 years, aging has become a major issue in many countries. In the U.S., operation for 60 years is permitted, and an application for 80 years of operation has been submitted. Nuclear power generation in the world gradually increased until 2015, and the ratio of nuclear-generated power is the recent lowest at 11.0% in 2015. As of August 2018, there are 55 nuclear reactors under construction in 17 countries, of which China has the largest at 38. There are a total of 48 abolished units, including 18 in Japan and 10 in Germany. In the future, nuclear power generation is expected to expand in Asia, Eastern Europe, and Russia. As a trend, the economic efficiency of nuclear power generation is deteriorating due to shale gas in the U.S. In France, the goal is to reduce the nuclear power generation ratio to 50%, but the outlook is uncertain. China plans the commercial operation of state-of-the-art nuclear power plants with an expectation of exporting to overseas, and is further developing third generation reactors, high-temperature gas reactors, etc. This paper also touches on the situation of each of Russia, South Korea, the U.K., India, etc. (A.O.)
[en] A deliberative poll (DP) is a new type of democratic process in which citizens selected at random from the voters are educated on and discuss given political issues, and then the results are reflected in policy. An example of this occurred in 2012 when the Japanese government conducted a DP on nuclear power generation goals for 2030. As a result, support for abolishing nuclear power increased significantly. On the other hand, in 2017, the Korean government conducted a DP on the construction of the Shin-Gori nuclear reactors and on future nuclear policy. As a result, support for the continued construction of the reactors and phase out of nuclear power was strengthened. In Japan's DP compared with that of Korea's, Japan's selected citizens were far less representative of the population, stakeholder's involvement was nonexistent, and the government was much less committed. (author)
[en] In view of the practical importance of the drift-flux model for two-phase flow analysis in general and in the analysis of nuclear-reactor transients and accidents in particular, the distribution parameter and the drift velocity have been studied for two-phase flow regime in a vertical large-diameter pipe. This study performed local measurements of the flow parameters (such as void fraction, gas velocity and liquid velocity) in a vertical upward air-water two-phase flow in a pipe of 200 mm inner diameter and 24 m in length by using the local sensor techniques such as optical multi-sensor probe and hot-film probe. The two-phase flow regimes in a vertical large-diameter pipe were classified into bubbly, churn and cap-turbulent flows according to the visual observation. The values of the distribution parameter and drift velocity were determined directly by their definition using experiment data of the local flow parameters in a two-phase flow in a large diameter pipe. Various existing drift-flux correlations were compared with present experimental results and the experimental data obtained by other researchers. A detailed discussion on the problems of these correlations was carried out in this paper. (author)
[en] In view of practical importance of the drift flux model for two-phase flow analysis in general, and in the analysis of nuclear reactor transients and accidents in particular, the distribution parameter, and the drift velocity have been studied for two-phase flow in a vertical large diameter pipe. In this, study, local measurements were performed on flow parameters, such as void fraction, gas velocity and, liquid velocity in a vertical upward air-water two-phase flow in a pipe of 200 mm inner diameter and, 25 m in height by using the local sensor techniques such as hot-film probes, optical multi-sensor, probes and differential pressure gauges. Two-phase flow regimes in a vertical large diameter pipe, were classified into bubbly, churn and slug flows according to the visual observation. The values of the, distribution parameter and the mean drift velocity were determined directly by their definition using experiment data of the local flow parameters in a two-phase flow in a large diameter pipe. Various existing drift flux correlations were compared with the present experimental results and experimental data obtained by other researchers. A detailed discussion on the problems of these correlations was presented in this paper.