Published online by Cambridge University Press: 19 October 2011
The rapid release of activity when water firsts contacts the spent fuel surface in disposal will depend on the pellet microstructure at the arrival time of water in the container. Research performed on spent fuel evolution in a closed system has shown that the evolution of microstructure under disposal conditions should be governed by helium behavior with the cumulated α{decay damage. The evolution of fission gas bubble characteristics under repository conditions has been assessed. In UO2 fuels with a burnup of 47.5 GWd/t, the pressure of fission gas bubbles with the input of helium atoms should not reach the critical bubble pressure, thus micro-cracking in grains is not expected.