Irradiation effects on the leakage of rare gases from uranium dioxide

Results of experiments are considered, aimed at checking the effect of fuel irradiation on the leakage rate of gaseous fission products which have been carried out on the reactor loop of the first in-the-world NPP. During experiments the nonhermetic fuel element made of sintered uranium dioxide has been irradiated in vacuum at temperatures of up to 1730 deg C. Curves showing variations in leakage rates of Xe-133, Xe-135 and Kr-88 noble gases, and the curve of their common gamma activity after reactor shutdown and operation at the nominal power are presented. A conclusion is drawn that the reactor shutdown results in increase of the gas leakage rate with a subsequent decrease. The same regularity is observed when increasing the reactor power. Maximum leakage rates are observed at fuel temperatures ranging from 1000 to 1200 deg C. It is emphasized that during irradiation the fission rate of 4x1012 fis/sxcm3 at burnsups of up to 3x1018 fis/sxcm3 is sufficient to partially suppress the leakages of noble gases from the fuel