報告書番号

T93003

タイトル（和文）

沸騰伝熱隙間部の不純物濃縮挙動（その１）－沸騰大気圧条件下における不純物の濃縮測定への電気化学的手法の適用－

タイトル（英文）

Impurity Concentration on Boiling Heat Transfer Surface in Tube-tube Support Plate Crevice(Part1)-Application of Electrochemical Technique to Measure the Concentration Factor under Boiling Atomospheric Condition-

概要 （図表や脚注は「報告書全文」に掲載しております）

ＰＷＲプラントにおいて給水中に微量に溶解している不純物が蒸気発生器の伝熱管と管支持板との隙間部で著しく沸騰濃縮し、伝熱管に局部腐食が発生している。本研究の目的は、電気化学手法を用いて不純物の濃縮をその場で測定することである。本報告では、実機と同一形状のインコネル６００合金伝熱管と４０５ステレンス鋼支持板との隙間部の腐食電位測定から濃縮度を算出し、濃縮に及ぼす熱流束および水質の影響に関し、同手法の適用可能性を１００℃の種々の脱気水溶液中で基礎的に検討し、以下の結果を得た。（１）６００合金の腐食電位は、熱流束の増加に伴いアルカリ水溶液中では下がり、酸性水溶液中では上昇した。これより、アルカリでは隙間部にｐＨが増加し、酸性では減少するものと考えられ、本手法は沸騰濃縮の評価に適用可能であることがわかった。（２）濃縮度は熱流束の増加に伴い増加し、アルカリの方が酸性に比べ顕著であった。

概要 （英文）

Local corrosion has been experienced on the secondary side of steam generator tubes in tubetube support plate crevice of PWR's,because the impurities which were slightly dissolved in feed water have been concentrated in the crevice.Various chemical analyses have been applied to evaluate water quality in the crevice,however,it has been very difficult to analyze exactly due to their indirect analysis.In this report,the impurities concentration factors were calculated from the results of corrosion potential measurements in the crevice,and the effects of heat flux and water quality on the impurities concentration were examined,by using electrochemical method. The electrochemical corrosion potential of alloy 600 in the crevice were measured in deaerated sodium hydroide,sulfuric acid and magnesium chloride aqueous solutions at 100ﾟC.The main test results are as follows:(1)Corrosion potential of alloy 600 decreased with increasing heat flux in deaerated sodium hydroide solution,whereas increased with increasing heat flux in deaerated sulfuric acid and magnesium chloride solutions. The test results showed that,pH of the solution in the tubetube support plate crevice increased with increasing heat flux under deaerated caustic condition,while decreased with increasing heat flux under deaerated acidic conditions.So the electrochemical method was applicable to investigation on the evaluation of the impurities concentration behavior in the crevice.(2)From the calculated results,it was revealed that the concentration factor was increased with increasing heat flux,and compared with the case of acidic solution,impurities concentration in caustic solution was remarkable.

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