Identification of Radial Position of Fission Gas Release in High-Burnup Fuel Pellets under RIA Conditions

摘要

The radial positions of fission gas release (FGR) in high-burnup fuel pellets were examined after pulse irradiations that simulated reactivity-initiated accident (RIA) conditions in the Nuclear Safety Research Reactor (NSRR). The molar ratio of xenon (Xe) to krypton (Kr) (Xe/Kr ratio) in the released gas showed that fission gas was released from the entire region of the pellets of the examined PWR fuels during the pulse irradiations. On the other hand, most fission gas was released from the center and/or intermediate regions of the examined BWR fuel pellets. The analyses of the thermal stress distribution in fuel pellets during the pulse irradiations were carried out by means of a computer code, and the results supported the FGR positions that were estimated from the measured Xe/Kr ratios. Consequently, it is likely that fission gas is not released selectively from the rim structure at the pellet periphery under RIA conditions.