Shibata, Masahiro; Sawada, Atsushi; Tachi, Yukio; Makino, Hitoshi; Hayano, Akira; Mitsui, Seiichiro; Taniguchi, Naoki; Oda, Chie; Kitamura, Akira; Osawa, Hideaki; et al.
JAEA-Research 2012-032, 298 Pages, 2012/09
JAEA and NUMO have conducted a collaborative research work which is designed to enhance the methodology of repository design and performance assessment in preliminary investigation phase. The topics and the conducted research are follows; (1) Study on selection of host rock: in terms of hydraulic properties, items for assessing rock property, and assessment methodology of groundwater travel time has been organized with interaction from site investigation. (2) Study on development of scenario: the existing approach has been embodied, in addition, the phenomenological understanding regarding dissolution of and nuclide release from vitrified waste, corrosion of the overpack, long-term performance of the buffer are summarized. (3) Study on setting nuclide migration parameters: the approach for parameter setting has been improved for sorption and diffusion coefficient of buffer/rock, and applied and tested for parameter setting of key radionuclides. (4) Study on ensuring quality of knowledge: framework for ensuring quality of knowledge has been studied and examined aimed at the likely disposal facility condition.
Yui, Mikazu; Ishikawa, Hirohisa; Watanabe, Atsuo*; Yoshino, Kyoji*; Umeki, Hiroyuki; Hioki, Kazumasa; Naito, Morimasa; Seo, Toshihiro; Makino, Hitoshi; Oda, Chie; et al.
JAEA-Research 2010-015, 106 Pages, 2010/05
This report summarizes the activity of Phase I of Waste Management Working Group of the United States - Japan Joint Nuclear Energy Action Plan started in 2007. The working group focused on consolidation of the existing technical basis between the U.S. and Japan and the joint development of a plan for future collaborative activities. Firstly, the political/regulatory frameworks related to nuclear fuel cycles in both countries were reviewed. The various advanced fuel cycle scenarios in both countries were surveyed and summarized. Secondly, the waste management/disposal system optimization was discussed. Repository system concepts for the various classifications of nuclear waste were reviewed and summarized, then disposal system optimization processes and techniques were reviewed, and factors to consider in future repository design optimization activities were also discussed. Finally the potential collaboration areas and activities related to the optimization problem were extracted.
Yokoyama, Yutaka*; Mitsui, Hiroyuki*; Takahashi, Rieko; Taniguchi, Naoki; Asano, Hidekazu*; Naito, Morimasa; Yui, Mikazu
JAEA-Research 2008-072, 232 Pages, 2008/10
It is possible that the corrosion resistance at the overpack welds is different from that at base metal due to the differences of material properties. In this study, corrosion behavior of welded joint for carbon steel was compared with base metal using the specimens taken from welded joint model fabricated by TIG (Tungsten Arc Welding, GTAW), MAG (Gas Metal Arc Welding, GMAW) and EBW (Electron Beam Welding) respectively. The results of these corrosion tests indicated that the corrosion resistance to general corrosion, pitting corrosion and crevice corrosion at welded metal of TIG and MAG was inferior to base metal. No deterioration of corrosion resistance was observed in any corrosion modes for EBW, which does not need filler material. Neither the base metals nor the welds is not susceptible to SCC under the carbonate concentration near that of the disposal environment.
Mitsui, Hiroyuki*; Takahashi, Rieko*; Taniguchi, Naoki; Otsuki, Akiyoshi*; Asano, Hidekazu*; Yui, Mikazu
JAEA-Research 2006-080, 322 Pages, 2006/12
There is some possibility that the corrosion resistance of overpack welds is different from that of base metal due to the differences of material properties. In this study, corrosion behavior of welded joint for carbon steel was compared with base metal using the specimens taken from welded joint model fabricated by TIG, MAG and EBW respectively. The corrosion tests were performed for following four items. (1) Passivation behavior and corrosion type, (2) Propagation of general corrosion, pitting corrosion and crevice corrosion under aerobic condition, (3) Stress corrosion cracking susceptibility, (4) Propagation of general corrosion and hydrogen embrittlement under anaerobic condition. The results of these corrosion tests indicated that the corrosion resistance of welded metal by TIG and MAG was inferior to base metal for general corrosion, pitting corrosion and crevice corrosion. It was implied that the filler materials used for welding affected the corrosion resistance. No deterioration of corrosion resistance was observed in any corrosion modes for EBW, which does not need filler material. The susceptibility to stress corrosion cracking of welded metal and heat affected zone was lower than that of base metal.
Ishikawa, Hirohisa; Igarashi, Hiroshi; Umeki, Hiroyuki; Shimizu, Kazuhiko; Miyahara, Kaname; Ishimaru, Tsuneari; Mitsui, Seiichiro
Proceedings of 6th Pacific Rim Conference on Ceramic and Glass Technology (PacRim6) (CD-ROM), 17 Pages, 2006/09
Final disposal of high-level radioactive waste is essential issue to utilize nuclear energy. JNC has promoted the research and development on disposal technology to contribute to the implementation and safety regulation in the implementation phase after the legislation of the Act on final disposal. The field of the R&D covers geological environment, engineering of geological disposal and performance assessment. As to the two underground laboratories (URLs), surface-based investigations have been carried out and the constructions of both have already started. On the basis of these investigations, geologic environmental models have been developed. The study on natural phenomena such as volcanism and faulting has been conducted. In the above ground research facilities, the development of advanced models, databases for the long-term evolution of the near-field and engineering technologies has been carried out. In terms of safety assessment methodologies, development of relevant databases and advanced safety assessment models and techniques has been carried out. The H17 report will be published in autumn 2005 for the studies conducted in the surface-based investigation phase at the URLs.
Mitsui, Hiroyuki*; Taniguchi, Naoki; Otsuki, Akiyoshi*; Kawakami, Susumu; Asano, Hidekazu*; Yui, Mikazu
JAEA-Research 2006-031, 88 Pages, 2006/06
The corrosion experiments for welded carbon steel were planed to contribute to an assessment of long-term integrity of carbon steel overpack welds considering corrosion damage specific to overpack welds. Based on this plan, electrochemical tests for welded carbon steel using the samples welded by EBW and TIG were carried out, and the corrosion behavior of welded zone was compared with that of base metal. The results of anodic polarization tests in 0.01M and 0.1M carbonate aqueous solutions for base metal, heat affected zone and welded metal indicated that; -As for EBW, the anodic polarization curves were not affected by welding although the metallurgical structures vary with base metal, heat affected zone and welded metal. -As for TIG, the current density of welded metal was larger than that of base metal and of heat affected zone, and local dissolution with immediate increase in current density was observed in 0.01M-pH10 carbonate aqueous solution.
Konishi, Hiroyuki; Shiwaku, Hideaki; Yoneda, Yasuhiro; Mitsui, Takaya; Nishihata, Yasuo
SPring-8 Riyosha Joho, 4(5), p.4 - 8, 1999/09
no abstracts in English
Mitsui, Hiroyuki*; Takahashi, Rieko*; Otsuki, Akiyoshi*; Asano, Hidekazu*; Taniguchi, Naoki; Yui, Mikazu
no journal, ,
The slow strain rate tests(SSRT) of carbon steel were performed in sodium carbonate-sodium-bicarbonate aqueous solution to acquire knowlwdges regarding susceptibility to stress corrosion cracking of welded joint of carbon steel overpack for high-level radioiactive waste disposal. The specimens were taken from thick cylindrical sample welded by TIG and EBW, and then SSRT tests were applied to the each of specimens of base metal, heat affected zone and welded metal. Based on the results, the susceptibility to stress corrosion cracking of welded joint of carbon steel overpack was evaluated.
Yokoyama, Yutaka*; Mitsui, Hiroyuki*; Takahashi, Rieko*; Otsuki, Akiyoshi*; Asano, Hidekazu*; Taniguchi, Naoki; Yui, Mikazu
no journal, ,
In Japan, carbon steel is one of the candidate materials for the disposal container (overpack) for high-level radioactive waste (HLW). Overpack seals vitrified waste and is required to isolate it from contact with groundwater for 1,000 years in Japan's waste management program. After overpack is placed in a deep underground repository, it is presumed that it will be exposed to environmental conditions which include lithospheric pressure from bedrock, hydrostatic pressure from groundwater and swelling pressure of the buffer material as mechanical forces and contact with groundwater as chemical conditions that may induce corrosion. Therefore, the wall thickness of overpack is designed with consideration for mechanical strength and corrosion property so that it can maintain its integrity for 1000 years. On the other hand, the overpack is enclosed by welding. With regard to the assessment of the applicability of welding techniques to the overpack, it is important to confirm the long-term integrity of the weld joint from the aspects of mechanical strength and corrosion property, too. In this study, the corrosion behavior of weld joints, which were provided by TIG (GTAW), MAG (GMAW) and EBW (Electron Beam Welding), was investigated by immersion tests under the aerobic conditions considering environment at the early stage of the repository.
Honda, Akira; Miyahara, Kaname; Makino, Hitoshi; Oda, Chie; Mitsui, Seiichiro; Umeki, Hiroyuki; Takase, Hiroyasu*
no journal, ,
Authers defined a process, in which the subjects for affecting the credibility of safety cases were explored, the subjects are defined as problems in the performnce assessment and the measures for solving the problems are proposed, as an "Exploratory Performance Assessment". The methodology of "Exploratory Performance Assessment" was introduced by showing an example relevant to the near field performance.
Omori, Hiroyuki; Maeda, Toshikatsu; Mitsui, Seiichiro; Bamba, Tsunetaka
no journal, ,
no abstracts in English
Maeda, Toshikatsu; Omori, Hiroyuki; Mitsui, Seiichiro
no journal, ,
Static leach tests were conducted for P0798 type simulated HLW glass in magnesium chloride solution to investigate the effects of Mg ion on the glass corrosion. The glass corroded at higher rate under the condition that Mg ion exists in the leachate, while the rate dropped after the depletion of Mg ion in the leachate. Surface analyses showed that altered layer including Mg and Si was observed at the surface of the leached glass. The present results implied that corrosion of the glass with the higher rate occurred as dissolution of Si from the glass network accompanied with formation of magnesium silicates. Corrosion rate of the HLW glass would be low for long-term if cations forming silicate compounds are scarce in groundwater.