New evaluation method of material degradation considering synergistic effects of radiation damage

照射の複合作用を考慮した新しい材料損傷評価法の開発

三輪 幸夫; 加治 芳行  ; 大久保 成彰   ; 近藤 啓悦  ; 塚田 隆 

Miwa, Yukio; Kaji, Yoshiyuki; Okubo, Nariaki; Kondo, Keietsu; Tsukada, Takashi

次世代の超臨界圧水高速炉の炉内構造材は現行の軽水炉よりも高温で高照射量まで使用されるため、照射損傷と熱応力による材料の劣化が設計の段階で適切な精度を取り込んで考慮されなければならない。現在の経験ベースの設計基準では、構造材料の寿命は、延性脆性遷移温度の上昇のような照射後試験から得られる材料劣化事象によって決定される。しかし、照射誘起応力腐食割れ(IASCC)などの材料劣化では、照射硬化,局所的な材料組成変化,スエリング及び照射クリープなどの材料劣化因子の複合作用の影響を考慮した、合理的な設計を行うことが望ましい。本研究では、IASCCによる材料損傷をより高い精度で予測するために、異なる照射量依存性を持つ材料劣化因子を照射誘起応力緩和に関してモデル化する。そして、そのモデルを用いて炉内構造材のIASCCによる損傷挙動を供用期間に渡ってシミュレーションする。本論文では、新しい材料損傷評価法の概念と材料損傷シミュレーションのための計算コードの概要を示した。

In core structural materials of next generation reactors, materials' degradation behavior by neutron irradiation damage and thermal (cyclic) stress should be considered with fair accuracy in design process (including maintenance and repair plans), because the materials are used under higher temperature gradients and higher neutron flux fields than those in the present light water reactors. In the current experiential design rules, service lives of core structural components were determined by the materials degradation such as the increase of ductile-to-brittle transition temperature after post irradiation examination data. However, other materials degradations such as irradiation-assisted stress corrosion cracking (IASCC) should be considered reasonably in the design process of the next generation reactors, because of the anticipation of the beneficial effects by synergistics of these radiation damage such as radiation hardening, local chemical composition change, swelling and radiation creep. To predict material failure by IASCC with reasonable accuracy, in this study, each material degradation phenomenon with different dose dependence was modeled with consideration of radiation induced stress relaxation. The models were integrated to simulate the failure behavior for the reactor operation period. In this paper, the models obtained by ion-irradiation experiments were presented, and the concept of new evaluation method and the programming code for the failure simulation were outlined.