Behavior of high burnup BWR UO fuels with additives under RIA conditions

高燃焼度添加物入りBWR用UO燃料の反応度事故時挙動

三原 武  

Mihara, Takeshi

JAEA have obtained regulatory data for advanced or further high burnup fuels in order to provide data and knowledge on fuel behavior needed for safety regulation. Two RIA tests on test rods with doped UO pellets (LS-4 and OS-1) which had been irradiated in commercial BWRs were successfully performed at room temperature condition. The doped UO pellets were designed to have a larger grain size compared to standard UO fuel with adding additives. The results of LS-4 and OS-1 tests showed no failure and failure, respectively. The fuel enthalpy increase at failure of OS-1 was lower than those obtained in the failure cases of the fuel rods with RX cladding in a cladding hydrogen content of 200-300 ppm. The result of transient fission gas release during LS-4 test suggested an effect of the large-grained fuel pellet. According to the post-test appearance and hydride morphology in the cladding of the reference rod of OS-1, one of the reasons why the OS-1 showed the low fuel enthalpy increase at failure may be the decrease in the failure limit of the cladding tube due to the hydrides precipitated and radially oriented in the tube wall.