報告書番号

T97035

タイトル（和文）

ＰＷＲ２次系への酸素処理法適用に関する基礎的検討（その１）―伝熱管材料の隙間腐食に及ぼす溶存酸素の影響―

タイトル（英文）

RESEARCH ON APPLICABILITY OF OXYGENATED WATER TREATMENT TO PWR SECONDARY WATER (PART 1) -THE EFFECT OF DISSOLVED OXYGEN ON THE CREVICE CORROSION BETWEEN SG TUBE AND TUBE SUPPORT PLATES

概要 （図表や脚注は「報告書全文」に掲載しております）

酸素処理法の最高溶存酸素濃度（Ｄ０）条件下で，伝熱管材料６００ＴＴ合金および６９０ＴＴ合金を用い，ＡＳＴＭ規格に準拠した■間腐食試験を実施し，以下の結論を得た。（１）．６００ＴＴおよび６９０ＴＴ合金の腐食の形態は，■間部および非■間部とも均一腐食であり，■間腐食の発生は認められなかった。また，■間部の腐食量は，非■間部より小さかった。（２）．ＤＯ２００ｐｐｂの条件下では，６９０ＴＴ合金の保護皮膜の形成は６００ＴＴ合金より遅く，耐食性も６００ＴＴ合金より若干劣った。（３）．オージェ分析およびＸ線回折分析結果より，ＤＯ２００ｐｐｂの酸化環境条件下では，６００ＴＴおよび６９０ＴＴ合金の表面に生成した腐食生成物は主にＮｉＦｅ２０４およびＮｉＯ化合物であった。これは，主要合金成分の１つであるクロムがイオンとして溶解するためと考えられる。

概要 （英文）

IN ORDER TO APPLY OXYGENATED WATER TREATMENT(OWT) TO THE FEEDWATER OF A PWR S SECONDARY SIDE, THE SUITABILITY OF THIS METHOD MUST BE CONFIRMED. THAT IS, IT IS NECESSARY TO DETERMINE, UNDER OWT CONDITIONS, WHETHER CREVICE CORROSION WILL OCCUR ON THE HEAT TRANSFER TUBES CURRENTLY EMPLOYED IN STEAM GENERATORS (SG). THE CREVICE CORROSION MEANS THAT THE METAL SURFACE AT A NARROWER CREVICE IS CORRODEDSELECTIVELY DUE TO IMPURITIES IN THE WATER. THERE ARE MANY SUCH CREVICES BETWEEN THE HEAT TRANSFER TUBES AND THE TUBE-SUPPORTING PLATES OF SG. THE IMPURITIES DISSOLVED IN BOILING FEEDWATER WILL BE CONCENTRATED INTHE CREVICES, AND THE CONCENTRATED SALTS MAY CAUSE CREVICE CORROSION, RESULTING IN LATENT DAMAGE TO ATOMIC POWER STATIONS. IN THIS STUDY, UNDER A CONDITION OF 200PPB (PH 9.5, 270OC) OF THE DISSOLVED OXYGEN, WE CONDUCTED RESEARCH ON THE ABOVE-METHIONED CREVICE CORROSION AND ON NONCREVICE CORROSION FOR COMPARSON. WE EXAMINED CREVICE AND NONCREVICE CORROSIONS FOR INCONEL ALLOYS 600TT AND 690TT, USED AS THE HEAT TRANSFER TUBER OF SG, AND CALCULATED THE CORROSION AMOUNT (MG/CM2) IN THE CREVICE AND NONCREVICE AREAS FROM THE DATA OBTAINED AFTER DEFILMING USING AN OXIDATION-REDUCTION METHOD. CONSEQUENTLY, THE FOLLOWING CONCLUSIONS WERE OBTAINED: (1).FOR ALLOYS 600TT AND 690TT UNDER THE EXPERIMENTAL CONDITIONS THERE IS ONLY THE UNIFORM CORROSION AND NO THE LOCAL CORROSION IN THECREVICE AND NONCREVICE AREAS; (2).CORROSION RATE IN THE CREVICE FOR ALLOYS 600TT AND 690TT AS WELL AS STAINLESS 304 IS LOWER THAN THAT IN THENONCREVICE AREAS. THEREFORE, ALL THREE MATERIALS ARE SUITABLE FOR USE IN A SG; (3).FORMATION OF PROTECTIVE OXIDE FILM ON 690TT IS SLOWER THANTHAT ON 600TT THAT IS, 690TT EXHIBITS POORER ANTICORROSIVITY THAN 600TT; (4).CORROSION PRODUCTS FORMED ON THE SURFACE OF THE ALLOYS 600TT AND690TT ARE MAINLY COMPOUNDS CONSTITUTED BY NIFE204 AND NIO.

報告者

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