An Extended Study on the Release of Radiogenic Helium-3 from Uranium Tritide

The release behavior of helium-3 (3He) from uranium hydride (U(HDT)3), formed from mixtures of protium, deuterium, and tritium of varying compositions, has been measured over a 15.7-year period. The observed 3He release behavior has been rationalized using the percentage 3He released and the ratio of retained 3He to effective uranium (3He/Ueff) and is found to show good agreement with previous data. New data further support the conclusion that 3He is only accumulated within the uranium (U) that reacted during hydrogen loading, irrespective of hydrogen isotope. The samples exhibited an early release proportion of approximately 5% of radiogenic 3He followed by an increasing 3He release profile over time reaching accelerated release, where newly formed 3He is directly released at about 0.5 He/Ueff. Desorption of hydrogen isotopes from an aged uranium hydride sample (0.48 He/Ueff) resulted in a significant amount of the remaining 3He trapped in the lattice being released. Two desorption cycles were found to remove the majority of the remaining 3He with only 3% remaining in the sample. Uranium hydride with a 3He concentration of 0.48 He/Ueff is suggested to have exhibited desorption at a lower temperature compared with uranium with a 3He concentration of 0.06 3He/Ueff.