Near surface vacancy defects in sintered polished UO2 disks

The cc decay of fission products formed in UO(2) nuclear fuel during in-reactor irradiation generates defects and large amount of helium. To predict the spent fuel evolution during the long term storage, the He behavior has to be understood in correlation with the defects properties. Slow positron beam coupled with Doppler broadening spectrometer was used to investigate near surface vacancy-defects in different sets of polished sintered uranium oxide disks, annealed in H(2)/Ar atmosphere at different temperatures in the 500 to 1400degreesC range. A thin layer of vacancy defects is detected near the surface in as-polished sintered disks. The size of vacancy defects is larger after annealing between 1000 and 1400degreesC. The interaction of hydrogen with these vacancy defects is discussed.