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鉛冷却炉における炉心材料の腐食に関する調査・検討

lnvestigation for corrosion behavior of core materials in lead cooled reactor

皆藤 威二

Kaito, Takeji

高速増殖炉(以下FBRという。)の実用化戦略調査研究の一環として、冷却材として鉛を用いた場合の炉心材料の腐食について調査を行い、次のような知見が得られた。1.鉛-リチウム環境下でのステンレス鋼の腐食はNiの溶出が主要因であるため、Ni量の多い高Ni鋼ではとくに腐食が大きく、つぎにオーステナイト鋼、そしてフェライト鋼と順に耐食性がよくなる。2.オーステナイト鋼の溶出速度Da(mg/mの2乗/h)、およびフェライト鋼の溶出速度Dfはそれぞれ「log10Da=10.7873-6459.3/T」「log10Df=7.6185-4848.4/T」として表される(T:温度(K))。これら各材料の溶出速度Dに基づき、「C=(D$$times$$t)/$$rho$$$$times$$10のマイナス3乗」として腐食量C($$mu$$m)を評価することができる(t:時間(hr)、$$rho$$:各材料の密度(g/cmの3乗))。3.上記評価式を用いてオーステナイト鋼およびフェライト鋼の腐食量を推定した結果、フェライト鋼に対しオーステナイト鋼の腐食は非常に大きく、400$$^{circ}C$$で約6倍、600$$^{circ}C$$以上になると20倍以上の腐食量となった。鉛-リチウム環境下での現実的な使用温度は、オーステナイト鋼で400$$^{circ}C$$(30000hrで約60$$mu$$mの腐食量)以下、フェライト鋼でも500$$^{circ}C$$(30000hrで約80$$mu$$mの腐食量)以下と考えられる。

The corrosion behavior of core materials in lead cooled reactor was investigated as the feasibility study for fast breeder reactor. The results are summarized as follows. (1)The corrosion of stainless steels under lead and lithium occurs mainly due to the dissolution of nickel. Consequently ferritic stainless steels have better resistance to corrosion under lead and lithium than austenitic stainless steels, and the corrosion resistance of high nickel steels is worst. (2)The dissolution rate, D(mg/m$$^{2}$$/h), is correlated with lead and lithium temperature, T(K), as log$$_{10}$$ Da = 10.7873 - 6459.3/ T and log$$_{10}$$Df = 7.6185 - 4848.4/T, where D a is the dissolution rate for austenitic steels and D f is for ferritic steels. lt's possible to calculate the corrosion thickness, C($$mu$$m), using the following correlation: C = (D$$times$$t)/$$rho$$$$times$$10$$^{-3}$$, where t is exposure time(hr) and $$rho$$ is density of the core matelial (g/cm$$^{3}$$). (3)The corrosion thickness estimated for austenitic steels using above correlations was extremely larger than ferritic steels, about 6 times at 400$$^{circ}$$C and more than 20 times at above 600$$^{circ}$$C. lt's considered that applicable temperature in lead cooled reactor core is below 400$$^{circ}$$C (about 60$$mu$$m corrosion thickness after 30000 hr) for austenitic steels, and below 500$$^{circ}$$C (about 80 $$mu$$m after 30000 hr) for ferritic steels.

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