Post irradiation-examination results for absorber material irradiation rig AMIR-6; The Results of non-destructive examination for capsules

Abe, Kazuyuki; Sasaki, Shinji  ; Kikuchi, Shin  ; Katsuyama, Kozo ; Nagamine, Tsuyoshi; Matsumoto, Shinichiro

Irradiation tests of Absorber Material Irradiation Rig (AMIR) have been continuously conducted, using the experimental fast reactor Joyo. AMIR-6, which was submitted for post-irradiation-examinations (PIE) this time, was irradiated in order to evaluate the limit of failure in control rods and confirm the effect of method for suppression of relocation caused by cracking of boron carbide (BC) pellets. According to this purpose, gap size between BC pellet and cladding tube (inner capsule tube), enrichment of B, thickness of cladding tube and its material were changed in this test. In addition, thin shroud tube wrapping BC pellets was used as the method for suppression of relocation. Capsules were loaded in compartments, which had the upper and lower stairs, and irradiation rig AMIR-6 was constructed of seven compartments in total. The irradiation capsule had double tubes, namely inner capsule tube and outer capsule tube. Between these tubes, sodium was filled. AMIR-6 was irradiated at the 6 raw in Joyo Mark-II core up to 10610 cap/m (max. burn-up) and 3.8210 n/m (max, fluence). Irradiation temperatures were evaluated from 530 to 890 C in design. Extraordinary results were observed for lower capsules by weight measurement performed. So, detailed visual inspection was carried out for these capsules. Consequently, sodium entered from the crack of screwhead attached to the outer tube in three irradiation capsules, whose weight increased. It was recognized that the sodium level between cladding tube and outer tube was lower in six capsules of lower stairs. Cladding crack was found out in three cladding tubes of lower irradiation capsule. It was suggested that the crack become for decrease of strength of cladding tube because those temperature increased at the position where sodium was not filled. The irradiation capsule using a shroud tube showed no diameter increase and ovality in the cladding.