Detailed characterisations of high burn-up structures in oxide fuels

In this paper, a series of post-irradiation examination results on high burn-up structures (HBS) are summarised for a wide variety of fuels (various programmes on PWR UO2 fuels with different claddings and with or without doping, PWR MOX fuels, FBR fuels, etc.). This summary is intended to provide a better understanding of how high burn-up structure is formed and subsequently changes up to very high burn-ups in various irradiation conditions. This paper also focuses on the existence of planar defects prior to the HBS formation and their change with time, as well as on the chemical influences and consequences of the HBS. Two new mechanisms are proposed to take into account these observations.