Leaching of irradiated UO2 fuel

Leaching tests over a period of 105 days have been performed on 20 mm long sections of an irradiated fuel rod. The sections - fuel with clad - were selected from axial locations along the rod corresponding to average linear heat ratings of 11.2 and 23.5 kW/m. For each fuel type, two leachant solutions were used: a synthetic Swedish groundwater and distilled water as reference. Leaching was performed at 60 deg C without mechanical stirring. All the leached species which were measured (U, Sr-90, Cs-137 and total alpha activity) showed large initial leaching rates - expressed as fractions of the total inventory leached per day - but the end of the leaching period, values were obtained of about 10-6/d for U, Sr-90 and Cs-137 and about 10-7/d for total alpha activity. Comparison of the cumulative amounts leached out during 105 days between the highly-rated and low-rated specimens showed the greatest difference in the case of Cs-137 where values of about 0,7 percent and 0,03 percent of the total Cs-137 inventory were obtained. These values demonstrate the sensitivity to heat rating of the movement of Cs-137 during reactor operation to the pellet-clad gap and pheripheral cracks