Fundamental research on behavior of helium in MA-bearing oxide fuel

Arai, Yasuo; Serizawa, Hiroyuki  ; Nakajima, Kunihisa  ; Takano, Masahide ; Sato, Isamu; Katsuyama, Kozo ; Akie, Hiroshi  ; Suzuki, Motoe; Shirasu, Noriko  ; Haga, Yoshinori   ; Akabori, Mitsuo

High amount of He is generated in MA-bearing fuel during irradiation and storage periods compared with that in U or U-Pu fuel. Laboratory scale experiments, post irradiation examinations and modeling study were carried out in order to understand the He behavior in MA-bearing oxide fuel. Diffusion characteristics of He in single-crystal UO were investigated by the Knudsen effusion mass spectrometry. Effects of the He accumulation on lattice and bulk expansion of oxide pellets were examined by use of alpha-decay of Cm. Post irradiation examinations of 0.5%Am-MOX fuel irradiated at a fast test reactor JOYO were carried out, concentrating on the He behavior in the fuel pellets. A model describing the He behavior in MA-MOX fuel was constructed based on the principle processes, such as generation, diffusion, equilibrium and release to outer gaseous phase. By use of the model as a subroutine of a conventional fuel behavior analysis code, the He behavior in MA-MOX fuel for fast reactors was simulated.