Hydrogen Absorption Behavior of the R-SUS304ULC/Ta/Zr Dissimilar Metal Joint Under NaOH Immersion

Abstract In reprocessing plants of Japan, Zr and ultra-low carbon 304 stainless steel (R-SUS304ULC) piping are connected by a joint formed by explosive bonding with Ta sandwiched between R-SUS304ULC and Zr. The joint exhibits excellent corrosion resistance during normal operation. However, Ta causes corrosion and generates hydrogen in NaOH solutions, which are used to decontaminate the equipment in reprocessing plants. This has led to concerns about hydrogen embrittlement of the joints via hydrogen absorption. The authors examined the hydrogen absorption behavior of pure Ta immersed in various NaOH solutions. However, there is a lack of studies on the hydrogen absorption behavior of such joints, and it is difficult to evaluate the amount of hydrogen absorbed by the joints under various decontamination conditions. In this study, we conducted immersion tests of the R-SUS304ULC/Ta/Zr joint in NaOH solution to investigate the effect of immersion environment on hydrogen absorption behavior. Electrochemical measurements were conducted to examine the hydrogen absorption environment. The results showed that the amount of hydrogen absorbed into Ta in the joints decreased compared with that in pure Ta, regardless of the immersion time. The galvanic current measurements of Ta connected R-SUS304ULC or Zr in an NaOH solution indicated that the hydrogen evolution reaction was separated to the R-SUS304ULC and Zr surfaces and that the hydrogen absorption of Ta was suppressed.