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Irradiation behavior of precipitation hardened Ni-base super-alloys with EHP grade under multi-ion irradiation

イオン照射によるEHP高Ni合金の照射損傷の研究

Kim, G.; 芝 清之; 沢井 友次; 井岡 郁夫; 木内 清

Kim, G.; Shiba, Kiyoyuki; Sawai, Tomotsugu; Ioka, Ikuo; Kiuchi, Kiyoshi

FaCT事業では、約250dpaの照射量に耐える燃料被覆管の候補材として9Cr系のODS鋼が選定されているが、粉末冶金に伴う製品の安定性や、再処理適合性の面での懸念も議論されている。本研究では、こういった懸念に対するバックアップ材料としての位置づけで、耐照射性とともに耐食性に優れる二種類($$gamma$$'析出型とG相析出型)の超高純度高Ni合金(EHP合金)を選定し、その開発を進めている。開発材の耐照射性を確認するために、高速炉での核変換反応に伴うHeやHの生成量を模擬した高崎量子応用研究所TIARAのイオン照射実験を実施した。その結果、400$$^{circ}$$C照射では$$gamma$$'析出型合金,G相析出型合金ともに照射硬化を示したが、G相析出型合金の方が照射硬化量は大きかった。また、550$$^{circ}$$C照射によるスエリングは両合金ともに良好であったが、特にG相析出型合金では大型のボイドが形成されず、極めて耐スエリング性が高いということが明らかになった。

The irradiation behaviour in two different precipitation hardening types of Ni-base alloys with the ultra high purity grade (EHP), namely, the $$gamma$$' type and G phase type was investigated by multi-ion beam techniques simulated to the irradiation conditions in fuel cladding tubes used in sodium cooled FBRs. Single ion-beam irradiation tests were conducted up to 90 dpa (by Fe$$^{3+}$$ or Ni$$^{3+}$$) at 673 K. Triple ion-beam irradiation tests were conducted up to 90 dpa (by Ni$$^{3+}$$, 90 appmHe and 1350 appmH) at 823 K. The irradiation behaviour was examined by nano-indentation tests to irradiation hardening, and the microscopic observation by TEM to the distribution of dislocations, cavities and voids. The behaviour was compared with those of PNC316. The dominating irradiation defects in EHP($$gamma$$') alloy at 673 K by single ion-beam are Frank loops, perfect unfaulted loops and line dislocations. Whereas, those of EHP(WSi) alloy are the irradiation-induced G phase precipitates along ${111}$ planes. Those dominating defect structures at 823 K by triple ion-beam are classified as followings, bimodal distributions in EHP($$gamma$$'), bubbles in EHP(WSi) and voids in PNC316. The ratio of void swelling is estimated as nearly 0.01% in EHP(WSi), 0.2% in EHP($$gamma$$'), 3.4% in PNC316. From those results, the excellent irradiation properties of EHP(WSi) alloy is clarified as the inhibition effects of secondary irradiation defects.

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