亜鉛注入冷却水中における材料腐食試験 (新型転換炉「ふげん」亜鉛注入時の材料健全性確認)

Material corrosion tests in the coolant with zinc addition; Confirmation of material integrity for zinc addition at ATR "Fugen"

天藤 雅之; 高城 久承 ; 小鷹 幸三; 北端 琢也

not registered; not registered; not registered; not registered

新型転換炉「ふげん」亜鉛注入時の材料健全性確認新型転換炉「ふげん」では、被ばく低減を目的に原子炉冷却水中に亜鉛を注入することが計画されている。冷却系に使用されている各種材料の亜鉛注入時における健全性を確認するため、原子炉冷却水模擬環境下で亜鉛注入(約10ppb)および無注入の材料腐食試験を各2,000h実施した。本試験により得られた主な結果は以下のとおりである。・圧力管材料であるZr-2.5%Nb 合金は、亜鉛注入により若干重量増加が大きくなる傾向を示したが、酸化による母材の肉厚減少量は1.3 m(100,000h外挿値で10m程度)であり、圧力管の健全性に影響をおよぼすレベルではない。腐食試験中の水素吸収は認められなかった。・ステンレス鋼では、亜鉛無注入時に腐食により重量が減少する傾向が認められ、耐蝕性の低い鋼種ほどその重量減少が明確であったが、亜鉛注入時はいずれも僅かな重量増加に転じ、亜鉛注入は腐食を抑制する方向であることが確認された。・腐食試験後の表面皮膜分析より、亜鉛注入により表面皮膜中に亜鉛が高濃度に濃縮され、その形態も変化することが明らかとなった。亜鉛注入の有無で認められた腐食量の差は、表面腐食生成物の組成および形態の差に起因すると考えられる。

Zinc addition to the coolant of the reactor core of ATR "Fugen" is being planned for the purpose of reducing the radiation exposures. In order to confirm the integrity of the materials used in the reactor coolant system, a matrerial corrosion test with zinc addition (10 ppb) and that without zinc addition were performed for 2,000 h under the condition simulating the reactor core of "Fugen". Main results obtained from these tests are as follows : (1)For Zr-2.5%Nb alloy used for the pressure tubes, weight gain during the corrosion test tended to be large by zinc addition. It was concluded that this weight gain would not affect the integrity the pressure tube, because the reduction of the thickness of the base metal was estimated around 1 m during the corrosion test (extrapolated value for 100,000 h was about 10m). The hydrogen absorption during the test was not observed. (2)Some specimens of stainless steels showed weight loss caused by metal release from corroded surface without zinc addition. This weight loss is clearly observed for less corrosion resistance steels. Since all of the specimens tested with zinc addition showed slight gain of the weight, it is confirmed that zinc addition suppressed the corrosion of stainless steels. (3)From surface analyses after the corrosion test, it was clarified that zinc was concentrated in the surface oxide film, and that the morphology was changed. It was considered that the difference of weight changes between the specimens corroded with zinc addition and that without zinc addition was attributed to the difference of the composition and the morphology of the surface oxide films.