Evaluation of crack growth rates and microstructures near crack tip of neutron-irradiated 316L stainless steels in simulated BWR environment

BWR模擬環境における中性子照射316Lステンレス鋼のき裂進展速度及びき裂先端近傍でのミクロ組織の評価

知見 康弘; 笠原 茂樹*; 西山 裕孝 ; 瀬戸 仁史*; 茶谷 一宏*; 橘内 裕寿*; 越石 正人*

Chimi, Yasuhiro; Kasahara, Shigeki*; Nishiyama, Yutaka; Seto, Hitoshi*; Chatani, Kazuhiro*; Kitsunai, Yuji*; Koshiishi, Masato*

照射誘起応力腐食割れ(IASCC)進展挙動を理解するため、中性子照射した316Lステンレス鋼試験片を用いて、BWR模擬水質環境(約290C高温水)中でき裂進展試験を実施し、試験片のき裂先端近傍での酸化皮膜特性及び変形組織について透過型電子顕微鏡(TEM)を用いて調べた。試験供給水の脱気及び水素注入により腐食電位(ECP)を低下させることで、き裂進展速度の低下とともに、き裂内での酸化が抑制されている様子が観察された。発表では、き裂進展に伴う変形組織の観察結果も示し、き裂進展速度と酸化皮膜特性、変形組織の関係について議論する。

In order to understand irradiation-assisted stress corrosion cracking (IASCC) growth behavior, crack growth tests in simulated BWR water conditions (at 563 K) were performed using neutron-irradiated specimens made of 316L stainless steels, and the oxide film properties and locally deformed structures near the crack tip have been investigated by transmission electron microscopy (TEM). When electrochemical corrosion potential (ECP) of the materials was lowered by deaeration and hydrogen injection into feed water, apparent suppression of oxidation inside the cracks was observed as well as suppression of the crack growth rate (CGR). In the presentation, the TEM results of the locally deformed structures along the cracks are also reported, and the relation among the CGR, oxide film properties, and locally deformed structures is discussed.