Clarification of Rim Structure Effects on Properties and Behaviour of LWR UO2 Fuels and Gadolinia Doped Fuels

At the peripheral region of high burnup fuel pellets, a crystallographic re-structuring is observed, commonly called the rim structure, which is characterized by the existence of highly dense small sub-grains, whose size is approximately 100 nm, and the accumulation of small pores with average size around 1 µm. This restructuring can influence the fuel performance including, e.g. fission gas release behaviour, temperature, hardness and density. In order to clarify the threshold burnup and temperature of rim structure formation and fuel performances of LWR UO2 fuels and gadolinia-doped ((U,Gd)O2) fuels whose usage is increasing for higher burnup in LWR, several post irradiation examinations such as scanning electron microscope (SEM) /transmission electron microscope (TEM) observation, density measurements, hot cell annealing and thermal diffusivity measurements are done. By SEM and TEM observations, it is clarified that the microstructure evolution and the burnup and temperature threshold of rim structure formation of (U,Gd)O2 fuels is not different from that of UO2 fuels. The density change of UO2 and (U,Gd)O2 fuels is almost similar, and the irradiation temperature does not affect the density change significantly. Fission gas release behaviour can be classified by the existence of rim structure, and the release behaviour between UO2 and (U, Gd)O2 fuels is almost same.

SONODA T.;  KAMEYAMA T.;  SASAHARA A.;  KITAJIMA S.;  NAUCHI Y.;  KINOSHITA M.;  RONDINELLA Vincenzo;  WISS Thierry;  HIERNAUT Jean-Pol;  PAPAIOANNOU Dimitrios;  SHEINDLIN M.;  STAICU Dragos; 

2007-10-16

Omnipress

JRC40841

https://publications.jrc.ec.europa.eu/repository/handle/JRC40841,