FPs release behavior from irradiated FBR MOX fuel

Nakagiri, Toshio  ; Sato, Isamu

Fission products (FPs) release behavior in the experiments (FP-1, FP-2) performed at JNC were evaluated from the viewpoint of source-term evaluation of FBR. Release fraction of FPs (Cs, Sb, Ru, Eu) in the experiments were calculated by NUREG-0772 model, and grain (hypothetical spheres) radius of fuel pellets and diffusion coefficient of FPs in grains for Booth model were calculated in the evaluation. Furthermore, the calculated values were compared with the values obtained in other experiments, The results of evaluation are summarized bellow. (1)The experiments (FP-1, FP-2) were performed in inert gas (Ar) condition, but FPs release fractions and diffusion coefficients in fuel grains almost agree with the values obtained in the other experiments which were performed in oxidized conditions. FPs release behavior in reduced condition containing such as sodium vapor are expected to be different from the behavior in FP-1 and FP-2. Some other experiments in reduced condition should be performed to investigate FPs release behavior in reduced conditions. Geometric grain radius obtained from metallographic images is used for the base data of diffusion coefficients evaluation, but the radius calculated from BET surface area is desirable. (2)Another release mechanism such as evaporation from the fuel pellet surface should be considered for more detailed evaluation of Cs composite and low volatile Ru and Eu release behavior, but, FPs chemical composition in fuel pellet, oxygen potential in carrier gas and FPs chemical composition in carrier gas, etc, should be evaluated in advance.