Development of inspection and repair technology for the micro cracks on heat exchanger tubes

Nishimura, Akihiko  ; Shobu, Takahisa  ; Oka, Kiyoshi; Yamaguchi, Toshihiko ; Shimada, Yukihiro; Mihalache, O. ; Tagawa, Akihiro ; Yamashita, Takuya

A prototype probe system with a hybrid optical fiber scope was designed for inspecting and re-pairing the micro cracks on heat exchanger tubes in fast breeder reactors (FBRs). It comprised a laser processing head combined with an eddy current testing unit. Ultrashort laser pulse ablation was used to remove work-hardened layers. And spot laser welding was used to repair the micro cracks. This system has both safe and economical options for the maintenance of FBRs because it extends the lifetime of the heat exchangers.