2018 Fiscal Year Final Research Report
Crystal structure and mechanical properties of the precipitate phase inducing embrittlement of nuclear reactor pressure vessel steels
| Project/Area Number |
16K06767
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Multi-year Fund |
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| Section | 一般 |
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| Research Field |
Structural/Functional materials
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| Research Institution | Kumamoto University (2018)
Tohoku University (2016) |
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Principal Investigator |
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| Co-Investigator(Kenkyū-buntansha) |
牟田 浩明 大阪大学, 工学研究科, 准教授 (60362670)
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| Research Collaborator |
SUZUDO Tomoaki
YAMAGUCHI Masatake
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| Project Period (FY) |
2016-04-01 – 2019-03-31
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| Keywords | 軽水炉 / 寿命 / 圧力容器 / 脆化 / 析出 |
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| Outline of Final Research Achievements |
The G-phase (Ni16Si7Mn6) is an intermetallic compound that precipitates in the form of nano particles in steels constituting the pressure vessel of nuclear reactors exposed to neutron irradiation for many years, causing their embrittlement, resulting in limiting the lifetime of entire power plants. Physical properties of the G-phase have been measured, for the first time, by using its single-phase ingot fabricated by means of arc melting. The G-phase was found to be brittle, and softer than iron in terms of the shear modulus. The melting point was found to be largely different from that shown in a calculation phase diagram, by as much as 700 degrees, indicating that existing thermodynamic database of the G-phase may not be correct. Based on this serendipitous discovery, the free energy of the G-phase has been attempted to determine by both experiments and ab initio calculations, with consideration of a magnetic phase transition where the G-phase becomes anti-ferromagnetic below 200 K.
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| Free Research Field |
材料工学
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| Academic Significance and Societal Importance of the Research Achievements |
本研究で得られた知見は、軽水炉圧力容器の脆化寿命予測に現在使用されているモデル（JEAC4201-2013）を、金属物理学の学術的観点から補強する。このモデルでは、脆化の要因となる照射誘起析出物と照射欠陥クラスタの形成量を照射時間の関数として計算し、オロワン機構やラッセルブラウン機構に基づいて材料の硬化量を導出し、それが臨界値に達したとき脆化に至ると仮定されている（Ludwig-Davidenkov-Orowan仮説）。硬化量は析出物（G相）がマトリックス（Fe）の剛性率の比に比例する。また、析出物の熱力学的データが正確でなければ、析出速度（駆動力）の見積もりに影響が生じるということになる。
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