Reduction in degree of absorber-cladding mechanical interaction by shroud tube in control rods for the fast reactor

Donomae, Takako  ; Katsuyama, Kozo ; Tachi, Yoshiaki  ; Maeda, Koji  ; Yamamoto, Masaya; Soga, Tomonori 

One of the challenges in developing a long-life control rod is to restrain absorber-cladding mechanical interaction (ACMI). Its lifetime was limited by ACMI, which is induced by the swelling and relocation of BC pellets. To restrain ACMI, a shroud tube was inserted into the gap between the BC pellets and the cladding tube. And sodium was selected as bonding material instead of helium to restrain increases in the pellet temperature. As a result of these improvements, the estimated lifetime of the control rod at Joyo was doubled. In this paper, the results of post irradiation examination are reported.