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Effects of $$gamma$$-ray irradiation and crevice-like shape on the corrosion of type 316L stainless steel in high-temperature water

高温水中でのSUS316Lの腐食に$$gamma$$線照射及びすき間形状が及ぼす影響

中原 由紀夫 ; 加藤 千明  ; 山本 正弘 ; 渡辺 敦志*; 布施 元正*

Nakahara, Yukio; Kato, Chiaki; Yamamoto, Masahiro; Watanabe, Atsushi*; Fuse, Motomasa*

原子炉内での高温水の放射線分解は、原子炉材料の腐食及び応力腐食割れを抑制するうえで重要な要因の一つと考えられている。しかしながら、腐食等の材料表面での反応やすき間等の形状が放射線照射を受けた高温水中での水化学に及ぼす影響については、環境を測定することが困難なため、ほとんど研究されていない。本研究では、水化学に対して$$gamma$$線照射及びすき間部模擬形状が及ぼす影響を評価するため、SUS316Lについて高温水中で腐食試験を実施した。試験では、試験片を288$$^{circ}$$Cの$$gamma$$線照射された高温水中に500時間浸漬した。$$gamma$$線の吸収線量率は、評価した結果30kGy h$$^{-1}$$だった。円板型試験片(直径16mm,厚さ0.5mm,表面#800研磨紙仕上げ)を、1枚単独と、すき間部を模擬するため2枚を重ね合わせて浸漬した。試験後の試験片表面をSEM, TEM,レーザーラマン分光装置で分析した結果、$$gamma$$線照射によって表面での鉄酸化物の析出が促進され、また、内層酸化物層の厚さが厚くなった。すき間部模擬環境に面した表面でも、$$gamma$$線照射によって表面酸化物の形態が変化した。

The irradiation effect to high-temperature water in nuclear power plant has been regarded as one of important issues for preventing corrosion and stress corrosion cracking of plant materials. However, the effects of surface reaction and configurations of material on irradiated high-temperature water chemistry have been studied little because of the difficulty of measuring the environment. In this work, we have done a series of corrosion tests of Type 316L stainless steel in high-temperature water in order to estimate the effects of $$gamma$$-ray irradiation and crevice-like shape on the water chemistry. Test specimens immersed in high-temperature water of 288 $$^{circ}$$C were $$gamma$$-ray irradiated for 500 hours. The absorbed dose rate of $$gamma$$-ray irradiation was estimated to be 30 kGy h$$^{-1}$$. The dimensions of the disk-like specimens were 16 mm in diameter by 0.5 mm in thickness. The surfaces of the specimens were mechanically finished with #800 emery paper. Sets of two specimens attached closely in order to simulate a crevice-like environment were also immersed. The surfaces of the specimens were analyzed using SEM, TEM, and laser Raman spectrometer. The results of surface analyses indicated that $$gamma$$-ray irradiation enhanced the precipitation of iron oxide on the surface and the thickness of inner oxide layer became thicker by $$gamma$$-ray irradiation. $$gamma$$-ray irradiation also changed the morphology of oxide on the surface faced to the crevice-like environment.

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