HIGH BURNUP CHANGES IN UO2FUELS IRRADIATED UP TO 83 GWD/T IN M5(R)CLADDINGS

® cladded fuels. Post-irradiation examination of high burnup UO2 pellets show an increase in the fission-gas release rate, an increase in fuel swelling, and formation of fission-gas bubbles throughout the pellets. Xenon abundances were quantified, and phenomena leading to this bubble formation were identified. All examinations provided valuable data on the complex state of the fuel during irradiation. They show the good behavior of these fuels, exhibiting various microstructures at very high burnups, none of which is likely to lead to problems during irradiation.