Study on target wastage for sodium-water reaction environment formed on periphery of adjacent tube in steam generator of sodium-cooled fast reactor; Composite oxidation-type corrosion with flow experiment using high-temperature sodium hydroxide

Kurihara, Akikazu ; Umeda, Ryota ; Kikuchi, Shin  ; Shimoyama, Kazuhito ; Ohshima, Hiroyuki

Sodium-water reaction would take place due to a breach of heat transfer tube in steam generator (SG) of sodium-cooled fast reactor (SFR), and the reaction jet may cause wear to the neighboring tubes by thermal and chemical effects, which is so-called target-wastage. Accordingly, failure propagation caused by target-wastage may potentially detract the secondary cooling system integrity. In previous study, a great number of target-wastage experiments have been carried out for candidate materials under practical SG operation conditions. Target-wastage rate was derived from macroscopic boundary factors of reaction jet. However, this mock-up approach is not versatile, and does not befit for large-scale SG design. Therefore, target-wastage should be focused for safety assessment of the various SG design. In this study, experiment apparatus and technique on composite oxidation type corrosion with flow (COCF), which is integral part of target-wastage, were constructed to figure out the separation effect of local wastage factors under the high temperature sodium hydroxide (NaOH) and sodium monoxide (NaO) environment mainly generated by SWR. The authors quantitatively evaluated the effect of material temperature and fluid velocity on COCF rate, and diffusion coefficient of Mod.9Cr-1Mo steel into NaOH-NaO. Besides, it was revealed that COCF was sodium-iron composite oxidation type corrosion from metallographic observation and element assay.