報告書番号

U01005

タイトル（和文）

輸送容器密封部縮尺モデルの海中腐食挙動

タイトル（英文）

Corrosion behavior of the Small Lid Model of Transport Cask in the Seawater

概要 （図表や脚注は「報告書全文」に掲載しております）

種々の寸法のすきま腐食試験片や輸送容器密封部を想定した小ﾓﾃﾞﾙ試験体(縮尺1/5)を海中に浸漬暴露し,すきま腐食速度評価式を提案するとともに,容器のﾊﾞﾘｱ効果に及ぼす腐食影響を調べた。①浸漬位置の溶存酸素量は年間約5～14 mg/lで,実輸送容器の航路上における海没水深200～3000ｍの腐食を厳しい側に代表できる。②少なくとも約1000日間はｺﾞﾑｶﾞｽｹッﾄで密封性能が保たれる。③蓋と本体との金属接触部のすきま間隔は, 約700日間の浸漬後においても浸漬前と同等の1.4～2.8μm（平均値）の小さな値を示し,環境影響評価で用いるﾊﾞﾘｱ性能の設定値10μmを余裕を持って確保できる。④小ﾓﾃﾞﾙ試験体のすきま腐食進行は非常に遅く,低合金鋼製ﾎﾞﾙﾄのｶﾞﾙﾊﾞﾆｯｸ効果によりｽﾃﾝﾚｽ製ﾌﾗﾝｼﾞの腐食が抑えられている。このため, 提案したすきま腐食速度評価式は安全側の評価を与える。

概要 （英文）

The natural exposure corrosion tests in the seawater using the small lid models(scale, 1/5) of typical transport cask and the other crevice corrosion test specimens with several sizes have been performed for about 1,000 days. An estimation formula of crevice corrosion rate was proposed, and the effects of corrosion behavior on the barrier performance of the cask were evaluated based on the test results. ① The Dissolved Oxygen (DO) value measured at the test site is about 5 to 14mg/l. Since the measured value is over the DO value at the sea bottom of 200 ｍ to 3000 ｍ depth in the shipping route, the test results can represent conservatively the corrosion behavior of the actual cask. ② The sealability has been maintained by rubber gasket for about 1000 days. ③ The space between cask body and cask lid shows very small average values(1.4 to 2.8μｍ) after about 700 days exposure, and even if the sealability is lost by deterioration of rubber gasket, measured values of the space can satisfy the assumed value of the space 10μm in the environmental impact assessment with enough margin. ④The measured crevice corrosion rate of the small cask lid models was very small, and the progress corrosion of the stainless steel’s flange was reduced by the Galvanic effect of the low alloy carbon steel’s lid bolts. So, the proposed estimation formula of crevice corrosion rate gives the sever side’s evaluation for the actual cask.

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