Densification and Swelling in UO_2 Pellets under Hydrostatic Pressure Condition
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The effect of hydrostatic pressure on the volume change in unirradiated UO<SUB>2</SUB> pellets has been examined using an out-of-pile high pressure annealing technique. The pellet volume change was generated by annealing UO<SUB>2</SUB> pellets at 1, 500°C and at higher or lower ambient external pressures of 10-150MPa Ar/0.2%H<SUB>2</SUB> gas than the sintering pressures of 50 or 100MPa at 1, 800°C. The pressure difference, ΔP, between bubble internal and external hydrostatic pressures during the annealing corresponded to a range of•101 to 82MPa. The volume change directly depended on the sign and magnitude of ΔP. More negative ΔP caused larger densification due to the shrinkage of the as-sintered bubbles. Almost no volume change was observed at nearly zero ΔP, and fuel swelling due to the bubble growth increased at more positive ΔP. The bubble shrinkage and growth data were analyzed by the rate equation of Hull and Rimmer. The fractional volume changes calculated by the model were in good accordance with the measured values in the wide range of -8 to +10%.
- Journal of Nuclear Science and Technology
Journal of Nuclear Science and Technology 35(11), 796-800, 1998-11-25
Atomic Energy Society of Japan