Properties of the high burnup structure in nuclear light water reactor fuel

The formation of the RIM- or High Burnup Structure (HBS) is possibly the most significant example of the restructuring processes affecting commercial nuclear fuel in-pile. The HBS forms at the relatively cold outer rim of the fuel pellet, where the local burnup is 2-3 times higher than the average pellet burnup, under the combined effects of irradiation and thermo-mechanical conditions determined by the power regime and the fuel rod configuration. The main features of the transformation are the subdivision of the original fuel grains into new sub-micron grains, the relocation of the fission gas into newly formed intergranular pores, and the absence of large concentrations of extended defects in the fuel matrix inside the subdivided grains. The characterization of the newly formed structure and its impact on thermo-physical or mechanical properties is a key requirement to ensure that high burnup fuel operates within the safety margins. This paper presents a synthesis of the main findings from extensive studies performed at JRC-ITU during the last 25 years to determine properties and behaviour of the HBS. In particular, microstructural features, thermal transport, fission gas behaviour, and thermo-mechanical properties of the HBS will be discussed. The main conclusion of the experimental campaigns is that the HBS does not compromise the safety of nuclear fuel during normal operations.

WISS Thierry;  RONDINELLA Vincenzo;  KONINGS Rudy;  STAICU Dragos;  PAPAIOANNOU Dimitrios;  BREMIER Stephan;  POEML Philipp;  BENES Ondrej;  COLLE Jean-Yves;  VAN UFFELEN Paul;  SCHUBERT Arndt;  CAPPIA Fabiola;  MARCHETTI Mara;  PIZZOCRI Davide;  JATUFF Fabian;  GOLL W.;  SONODA T.;  SASAHARA A.;  KITAJIMA S.;  KINOSHITA M.; 

2017-12-19

WALTER DE GRUYTER GMBH

JRC106875

0033-8230,   

https://publications.jrc.ec.europa.eu/repository/handle/JRC106875,   

10.1515/ract-2017-2831,