It is well-known that the current nuclear fuel should be tolerable to severe accidents to mitigate their consequence with maintaining the performances, and various concepts of new fuels were being suggested and developed under the name of accident tolerant fuels (ATF).
One of the focuses on the current UO₂ fuel pellet for light water reactor(LWR) is about its low thermal conductivity. The low thermal conductivity leads to increase thermal gradient in the fuel pellet and centerline temperature when in operation. Enhancing the thermal conductivity of UO₂ fuel pellet can be greatly attractive in the aspect of fuel performance and also for its safety margin. The fuel pellets with high thermal conductivity can reduce the mobility of the fission gases by lowered fuel temperature. In addition, a reduced temperature gradient within the pellet probably enhances the dimensional stability, with lower thermal stress of the fuel pellet. A thermal margin gained from the high thermal conductivity of pellet would be utilized in a safe operation of LWR or even load-follow operation also.
The goal of developments for ATF pellet at KAERI is to reduce radioactivity release from fuel pellet to fuel outside, and to increase operational and safety margin during normal operation and accident conditions. In order to achieve the goal, KAERI has developed UO₂-Mo composite pellets with enhanced thermal conductivity. Molybdenum metal particles were aligned in UO₂ pellets to form heat transfer paths for enhanced thermal conductivity in radial direction.
In this presentation, the thermo-physical properties of the UO₂-Mo composite fuel pellets were characterized with the variation of microstructure compositions.