Release Behavior of Decay Helium from Zirconium-Cobalt Tritide

In order to discuss the long-term reliability and safety of zirconium-cobalt (ZrCo) alloy for tritium (T) use, the release behavior of decay helium (³He) from ZrCo tritide has been investigated for one and a half years with a radio-gaschromatograph. The results show that the release fractions of the total decay ³He in ZrCo tritide are less than 3 % and has been almost constant for 18 months under the following conditions : the operating temperatures = 293 ∼ 523 K, the atom ratios (T/ZrCo) = 0.3 ∼ 1.4, and the number of hydrogenation-dehydrogenation cycles before tritiation = 1 ∼ 10. Moreover, residual decay ³He was not released even if ZrCo was heated to 873 K, though most of the tritium was released. It became clear that the decay ³He was quite immovable in ZrCo tritide under these experimental conditions.