The Solubility of Helium in Uranium Dioxide

A high-pressure furnace that operates up to 2000°C in the pressure range of 100 atm to 10⁻⁵ torr was designed and constructed to saturate UO₂ powder of 4-µm average particle size with ⁴He. The powder was then dissolved in a fused salt in an induction chamber. The released ⁴He was mixed with a known quantity of ³He, and the mixture was analyzed with a mass spectrometer to determine the ⁴He: ³He ratio, hence the original mass of ⁴He in the sample. The solubility of He in UO₂ at 1200 and 1300°C was found to be 6.71 × 10⁻⁴ and 3.23 × 10⁻⁴ cm³ (STP)/(g atm), respectively. It was also found that the He-UO₂ system obeys Henry's law. From a plot of He concentration as a function of time, the diffusion coefficient at 1200 °C was estimated to be 1.5 × 10⁻¹³ cm²/sec.