During irradiation in a nuclear reactor, the fuel pellet experiences non-uniform fission density and strong thermo-mechanical solicitations, which result in alterations and restructuring occurring non-homogeneously in the fuel volume. The irradiated fuel is characterized by a highly heterogeneous structure, and a corresponding heterogeneous distribution of phases and properties. One of the most significant restructuring processes affecting the fuel is the formation of the high burnup structure (HBS) occurring at relatively high local burnup and relatively low temperature [1]. At the optical and scanning electron microscopy level, HBS is characterized by subdivision of the original grains into sub-micron grains and in the formation of a new micron-size class of pores which collect the fission gas. The changes associated with the HBS formation extend to cover a broad range of scales, down to the nanometer level and up to the engineering scale. The macroscopic properties determining the performance and the safety behaviour of the fuel are affected by the presence of HBS. This paper presents highlights from fuel safety studies performed at JRC-ITU and in other laboratories applying a broad spectrum of PIE techniques. The technical challenges associated with the experimental characterization of highly radioactive irradiated fuel at a "multiscale" level are also discussed.

RONDINELLA Vincenzo;  WISS Thierry;  CAPPIA Fabiola;  MARCHETTI Mara;  PAPAIOANNOU Dimitrios; 

2016-06-30

American Nuclear Society (ANS)

JRC100299

https://publications.jrc.ec.europa.eu/repository/handle/JRC100299,