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The Effect of Residual Decontamination Reagent on Stress Corrosion Cracking of Austenitic Materials Under High Temperature Water

Masami Yajima, Naoaki Takashima, Sadaaki Sasaki, Satsuharu Takimoto

Nuclear Technology

Volume 56 / Number 1 / January 1982 / Pages 120-127


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Stress corrosion cracking (SCC) of austenitic materials has been investigated under high temperature water into which a trace level of chemical reagent for reactor process decontamination was injected to simulate residual chemical reagent in normal reactor cooling water. Creviced bend beam and 4-in. pipe tests have been performed with two kinds of concentrated-type reagents and two kinds of dilute-type reagents. It was found that concentrated-type reagents, when injected into high temperature water by 1/1000 of a specified concentration, work as an oxygen scavenger and significantly inhibit intergranular stress corrosion cracking in both sensitized Type 304 stainless steel and Inconel alloys 600 and X-750. Dilute-type reagents did not reduce dissolved oxygen (DO) at all and one of the reagents tested accelerated SCC in Type 304 stainless steel when injected into high temperature water by 1/1000 of a specified concentration. Another dilute-type reagent partially suppressed cracking of Type 304 stainless steel at the same residual reagent concentration. It is suggested that residual level decontamination reagent will work in two ways, depending on residual concentration. When residual concentration is rather high, it will work as an oxygen scavenger and will not have detrimental effects in terms of SCC; when reagent concentration is very diluted, it will accelerate cracking in heavily sensitized Type 304 stainless steel, regardless of the type or kind of decontamination reagent. This effect will be reduced in actual operation since the DO level is ∼0.2 ppm maximum in the normal reactor water.

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