著者

Masanori ARITOMI Toshihiro ADACHI Shigeki HOSOBUCHI Noriyuki WATANABE

出版者

一般社団法人 日本機械学会

雑誌

Journal of Power and Energy Systems (ISSN:18813062)

巻号頁・発行日

vol.6, no.3, pp.412-422, 2012 (Released:2012-10-16)

参考文献数

4

被引用文献数

1 2

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In the joint research and development of treatment systems of cooling water for cutting asphalt pavement surface with our authors' group, the liquid-solid separation technology by flocculating and settling technology, and the flocculants for the use of systems were developed. In this paper, the developed flocculating and settling technology and the flocculants are discussed first. Next, the demonstration tests of decontamination technology on the contaminated water in swimming pools in an elementary school located at Motomiya City, Fukushima Prefecture had been conducted by use of the stationary purification system of contaminated water and the flocculants compounding with or without iron ferrocianide developed by the preliminary test. It was clarified from the results that ionized cesium (Cs) rarely exists in the stagnant water in pools, ponds, lakes and so on at the time when nine months have passed since Fukushima Dai-ichi nuclear power plant accidents. Further, it is necessary to use the flocculants compounding iron ferrocianide in the case where ionized Cs exists in water. From the above-mentioned results, the following problems were pointed out: One problem was cyanide dissolution in the purified water and the other one was the dissolution from the dehydration sludge. Finally, the high-performance mobile purification units of contaminated water which is capable for carrying with trucks have been developed, and the demonstration test was performed in Minami-soma City, Fukushima Prefecture to purify the contaminated water in a pond and generated by the high-pressure water washing in a Public Hall. From the test results, it was made clear that the dehydration sludge separated by liquid-solid settling of the contaminated water of around 1,000Bq/l became a high radiation dose of about 185,000Bq/l.

著者

Kenji KAWAGUCHI Tomoaki UCHIYAMA Ken MURAMATSU

出版者

一般社団法人 日本機械学会

雑誌

Journal of Power and Energy Systems (ISSN:18813062)

巻号頁・発行日

vol.6, no.3, pp.378-393, 2012 (Released:2012-08-10)

参考文献数

25

被引用文献数

10

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Fault Tree and Event Tree analysis is almost exclusively relied upon in the assessments of seismic Core Damage Frequency (CDF). In this approach, Direct Quantification of Fault tree using Monte Carlo simulation (DQFM) method, or simply called Monte Carlo (MC) method, and Binary Decision Diagram (BDD) method were introduced as alternatives for a traditional approximation method, namely Minimal Cut Set (MCS) method. However, there is still no agreement as to which method should be used in a risk assessment of seismic CDF, especially for uncertainty analysis. The purpose of this study is to examine the efficiencies of the three methods in uncertainty analysis as well as in point estimation so that the decision of selecting a proper method can be made effectively. The results show that the most efficient method would be BDD method in terms of accuracy and computational time. However, it will be discussed that BDD method is not always applicable to PSA models while MC method is so in theory. In turn, MC method was confirmed to agree with the exact solution obtained by BDD method, but it took a large amount of time, in particular for uncertainty analysis. On the other hand, it was shown that the approximation error of MCS method may not be as bad in uncertainty analysis as it is in point estimation. Based on these results and previous works, this paper will propose a scheme to select an appropriate analytical method for a seismic PSA study. Throughout this study, SECOM2-DQFM code was expanded to be able to utilize BDD method and to conduct uncertainty analysis with both MC and BDD method.

著者

Tomoaki UCHIYAMA Kenji KAWAGUCHI Toshio WAKABAYASHI

出版者

The Japan Society of Mechanical Engineers

雑誌

Journal of Power and Energy Systems (ISSN:18813062)

巻号頁・発行日

vol.5, no.3, pp.360-375, 2011 (Released:2011-08-30)

参考文献数

20

被引用文献数

3 8

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The purpose of this study is to investigate the effects of the consideration of simultaneous occurrence of seismically induced events in Nuclear Power Plants (NPPs) such as failures of components due to seismic stress, seismically induced fire, and seismically induced internal flooding in seismic probabilistic safety assessment(PSA). The seismic risk is estimated in terms of the Core Damage Frequency (CDF) and the CDF is comprised of occurrence frequencies of accident sequences. In this study, two analytical methods, upper bound approximation (UBA) using minimal cut sets (MCSs) and direct quantification of fault tree using Monte Carlo simulation (DQFM) are selected for comparison. The results showed that the simultaneous occurrence of seismically induced events should be reasonably considered to assess the intersection and the union of these events. In addition, the Great Eastern Japan Earthquake and the Tsunami damaged NPPs on the Pacific Coast of Eastern Japan on March 11, 2011 will be examined in this study.