The pellet-cladding interaction (PCI) and cladding fatigue have been studied as possible fuel failure mechanism under load-following conditions. The power ramp rate, the amount of power increase and the maximum power level play important roles for the fuel integrity during load-following operation.
The RAMP code was developed by modifying the existing thermal and mechanical codes to analyze the stress and strain distribution in the fuel cladding, fatigue damage and the integrity of fuel rods under various operating conditions.
For daily load-following operations, it is predicted that the length of time to fuel failure due to PCI decreases with increasing maximum power level ; for example, the failure time is predicted to decrease from about 100 days to about 500 days when the maximum power level during load-following operation increases from 200 Watts/cm to 300 Watts/cm.
The pellet-cladding interaction rather than the cladding fatigue is predicted to be the limiting fuel failure mechanism under load-following conditions.
