Abstract
The Oak Ridge National Laboratory (ORNL) has developed the cyclic integrated reversible-bending fatigue tester (CIRFT) approach to successfully demonstrate the controllable fatigue fracture on high burnup (HBU) spent nuclear fuel (SNF) in a normal vibration mode. CIRFT enables examination of the underlying mechanisms of SNF system dynamic performance. Due to the inhomogeneous composite structure of the SNF system, the detailed mechanisms of the pellet-pellet and pellet-clad interactions and the stress concentration effects at the pellet-pellet interface cannot be readily obtained from a CIRFT system measurement. Therefore, finite element analyses (FEAs) are used to translate the global moment-curvature measurement into local stress-strain profiles for further investigation.
The major findings of CIRFT on the HBU SNF are as follows:
• SNF system interface bonding plays an important role in SNF vibration performance.
• Fuel structure contributes to SNF system stiffness.
• There are significant variations in stress and curvature of SNF systems during vibration cycles resulting from segment pellets and clad interactions.
• SNF failure initiates at the pellet-pellet interface region and appears to be spontaneous.
