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Journal Articles

Development of laser welding technology for fully austenite stainless steel

Takano, Katsutoshi; Koizumi, Norikiyo; Serizawa, Hisashi*; Tsubota, Shuho*; Makino, Yoshinobu*

Yosetsu Gakkai Rombunshu (Internet), 33(2), p.126 - 132, 2015/06

A radial plates (RP), which is used in Toroidal field (TF) coil in ITER, is significantly large, such as 13 m height and 9 m wide, but thin, such as 10 cm thick, and are made of full-austenite stainless steel. Even though they are very large structures, high manufacturing tolerances are required. In addition, it is required that each RP is fabricated every three weeks. Therefore, the authors develop efficient manufacturing methods of RP. The laser welding is selected as a welding method of RP. But the development of the high power laser welding technology is necessary to avoid hot cracking of the materials used for RP, namely full austenite stainless steel with high nitrogen content. The authors carried out trial aiming at an application of the laser welding to RP. As a result, it is effective to optimize the angle of inclination of the weld head. It also seems sensitivity of hot cracking can be less by optimizing the chemical composition of materials to use for RP. It was therefore demonstrated that the application of the laser welding technology in the full austenite stainless steel.

Journal Articles

Geochemical and grain-size distribution of radioactive and stable cesium in Fukushima soils; Implications for their long-term behavior

Saito, Takumi; Makino, Hisashi*; Tanaka, Satoru*

Journal of Environmental Radioactivity, 138, p.11 - 18, 2014/12

 Times Cited Count:64 Percentile:86.8(Environmental Sciences)

Radioactive cesium was predominantly found in the extract obtained by strong-acid dissolution and the extraction residue and was more concentrated in silt and clay grains. X-ray diffraction analyses revealed that micaceous minerals as well as kaolin minerals were predominantly dissolved by the strong-acid treatment. Correlation between the fraction of $$^{137}$$Cs and the content of micaceous minerals in different grain-size fractions of soil minerals suggests that micaceous minerals are responsible for the fixation of $$^{137}$$Cs in the soils. The isotopic ratio of $$^{137}$$Cs and $$^{133}$$Cs in the extract by strong-acid dissolution was more than three times smaller than those in the extracts by water, ion exchange, and reductive dissolution. This indicates that the distribution of $$^{137}$$Cs was not in the steady state in 2 y after the accident due to relatively slow fixation by the soil clay minerals.

Oral presentation

A Study on the volcanic scenario adapting the FEP analysis; Application to the eruption of Izu-Oshima volcano

Murakami, Makoto*; Kawamura, Makoto; Sasaki, Hisashi*; Makino, Hitoshi; Seo, Toshihiro; Nishimura, Takuya*; Umeda, Koji; Oi, Takao; Geshi, Nobuo*; Oikawa, Teruki*

no journal, , 

The volcanic scenario has mainly been conventionally examined from a viewpoint of empiricism based on the understanding of physics and/or scientific mechanism of volcanic activity. However, when a volcanic scenario is examined only based on the empiricism of a volcano, there is a possibility that the phenomena which the volcano had not experienced in the past may fall out from the scenario. Therefore, it is necessary to follow up omission by collecting information from various volcanoes. The purpose of this research is to develop the scenario analysis technique which can perform prediction of progress of volcanic activity by applying the FEP analysis technique examined by High level radioactive waste geological disposal. As a result, a volcanic scenario can be built by applying the FEP analysis technique. It was understood that the FEP analysis technique developed by geological isolation can apply also to the field of other technology. We will collect information further and apply this technique to other volcanoes. We consider improvement of the FEP analysis technique based on the result of this study.

Oral presentation

A Study on a methodology of volcanic scenario analysis applying FEP analysis

Murakami, Makoto*; Kawamura, Makoto; Makino, Hitoshi; Geshi, Nobuo*; Oikawa, Teruki*; Sasaki, Hisashi*; Seo, Toshihiro; Nishimura, Takuya*; Umeda, Koji; Oi, Takao

no journal, , 

no abstracts in English

Oral presentation

New small sodium leak detection system, 2; An Experiment of moving fluid ionization detector and laser leak detector in fast breeder reactor Monju

Okazaki, Koki*; Naito, Susumu*; Nakayama, Kunihiko*; Makino, Shunichiro*; Shigeyama, Musashi*; Kuwako, Akira*; Izumi, Mikio*; Ito, Jun*; Okada, Hisashi*; Muto, Keitaro

no journal, , 

In fast breeder reactor (FBR), it is important to detect a small sodium leak surely for safety. As the coolant sodium used in FBR is low pressure, a small leak occurs from a crack before a pipe breaks, therefore it is possible to detect a sodium leak so as to shutdown a reactor before a pipe completely breaks. The sodium leaking from piping of cooling system reacts with oxygen etc. including with the ambient gas to form aerosols. In the second coolant system of the prototype liquid metal FBR Monju, the ambient air around piping is drawn into radiative ionization detector (RID). When sodium aerosols are detected by RID, chemical analysis of aerosols and the viewing of the leak point are carried out, then sodium leak is confirmed. As the signal of RID depends on temperature strongly and RID detects the aerosols which do not include sodium, the improvements of RID are demanded for reliability. Moving fluid ionization detector (MID) and laser leak detector (LLD) have been developed to improve these points. MID can reduce the dependence for temperature of the signal strength, and LLD can detect sodium atoms which are included in aerosols by means of laser-induced breakdown spectroscopy. An experiment was carried out for validating sodium leak detection system with MID and LLD under real environment installed in the second coolant system of Monju. In the experiments, sodium was not leaked, and ambient air around piping of the secondary coolant system was introduced through actual sampling line and measured by MID and LLD. In addition a sodium level in the ambient air was measured by means of ion chromatography. The experiment showed that the background signals of MID and LLD were stable and low and that the sodium level due to the background of salinity (NaCl) contained in the ambient air was lower than three orders of magnitude than the sodium level for small sodium leak. The plant applicability of MID and RID was validated by this experiment.

Oral presentation

A Study on a methodology of volcanic scenario analysis applying FEP analysis; A Case study

Murakami, Makoto*; Kawamura, Makoto*; Makino, Hitoshi; Geshi, Nobuo*; Oikawa, Teruki*; Nishimura, Takuya*; Umeda, Koji; Sasaki, Hisashi*; Seo, Toshihiro; Oi, Takao*

no journal, , 

The prediction technique of the volcanism is requested from the viewpoint of disaster prevention now. The prediction method using the volcanic scenario has been paid to attention. The purpose of this study is to develop the methodology of the volcanic scenario construction that the progress of the volcanic activity is predictable by progressively applying the FEP analysis methodology in the research of HLW geological disposal to the volcanic activity. A basic concept is as follows. We resolve the phenomena to compose the volcanic activity to the single-process referring to past volcanic eruptions. The single-process is arranged to the logical function theory. And, the development of volcanic scenarios is expressed as a chain of the functions. As a result, we developed adaptable volcano scenarios to the purpose. Moreover, it could be expected that the observations are made more effective by feeding back this methodology to the field survey.

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