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照射下における高Ni鋼の微細組織安定性に関する研究

Precipitate stability and swelling resistance of high-nickel alloy during irradiation

井上 利彦 ; 山下 真一郎   ; 山県 一郎 ; 吉武 庸光 ; 皆藤 威二 ; 関尾 佳弘  ; 林 長宏

Inoue, Toshihiko; Yamashita, Shinichiro; Yamagata, Ichiro; Yoshitake, Tsunemitsu; Kaito, Takeji; Sekio, Yoshihiro; Hayashi, Takehiro

高Ni鋼は、良好な耐スエリング特性を有していることから燃料被覆管材料として開発されており、代表的な商用鋼の一つであるNimonic PE16($$gamma$$'(Ni$$_{3}$$(Ti,Al))析出型)は、英国の高速原型炉(PFR)にて約148dpaまでの照射実績を有している。その一方、高Ni鋼は、照射や高温熱時効に伴う延性の低下が課題であり、$$gamma$$'析出物の粗大化や粒界での再析出がその要因の一つとされている。そこで、PE16の課題を克服するため、PE16で利用している$$gamma$$'析出型とは異なる炭窒化物析出型の高Ni鋼(15Cr-35Ni鋼)と、$$gamma$$'よりも安定と考えられる$$gamma$$"(Ni$$_{3}$$Nb)を加えた$$gamma$$'/$$gamma$$"析出型の高Ni鋼(15Cr-43Ni鋼)の2鋼種を新たに開発し、各種材料特性評価を進めている。本研究では、系統的な条件での照射試験が可能な原子力機構高崎量子応用研究所イオン照射研究施設(TIARA)にてイオン照射を行い、新規に開発した高Ni鋼の照射下における微細組織安定性(耐スエリング性など)を評価し、相対比較材であるPNC316鋼よりも耐スエリング特性に優れることを確認した。

Precipitation-strengthened high-nickel alloys have been developed for fuel cladding material in advanced reactor because of their intrinsic superior swelling property. In most case, Nimonic PE16 and these high-nickel alloys are strengthened by an intermetalic compound such as ordered phase gannma- formed in the matrix. The most important issue in development of high-nickel alloy is considered to be the improvement of mechanical properties at elevated temperature; the significant ductility loss due to irradiation at high temperature. The cause of this problem was believed to be the re-distribution of ordered phase gannma- and solute segregation to defect sink sites, such as grain boundary, dislocation and void surface, during irradiation. In this study, several types of precipitation-strengthened high-nickel alloys, which were stabilized by were carbide/nitride and gannma double prime phase, were developed and then the phase stability (precipitate stability and swelling resistance) in these alloys during irradiation was evaluated by utilizing TIARA facility. In the results, high nickel steel were confirmed more higher resistance of swelling than PNC316 steels.

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