Hydrogen absorption behavior of the R-SUS304ULC/Ta/Zr dissimilar metal joint under NaOH immersion

Ishijima, Yasuhiro ; Ueno, Fumiyoshi  ; Abe, Hitoshi ; Igarashi, Takahiro  

In reprocessing plants of Japan, Zr and R-SUS304ULC piping are connected by a joint formed by explosive bonding with Ta sandwiched between R-SUS304ULC and Zr. The other hands, Ta corrodes with hydrogen evolution 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. 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, immersion tests were conducted to the joint in NaOH solution to evaluate hydrogen absorption. 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. The galvanic current measurements of Ta connected with R-SUS304ULC or Zr in 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.