A modified tritium trick technique for doping vanadium alloys with helium

A modified tritium trick technique was used to implant three different levels of 3He in V-15Cr-5Ti (% by weight) and Vanstar-7 specimens before irradiation in the Fast Flux Test Facility (FFTF). The modifications include: wrapping of the specimens with tantalum foil to minimize oxygen contamination, and a 4000C decay-time treatment to prevent vanadium tritide formation and to produce a 3He bubble distribution similar to that produced during elevated temperature irradiation. Preliminary results show that both modifications were successful. However, the tritium removal step at 7000C, especially at higher helium levels, allowed large 3He bubbles to form in the grain boundaries and severely embrittled the V-15Cr-5Ti alloy. A better microstructure for simulation purposes can probably be produced by lowering the tritium removal temperature. Vanstar-7 specimens consistently absorbed about half as much tritium, and subsequently contained half as much 3He as V-15Cr-5Ti. Implanting 3He in vanadium alloys via the tritium trick offers a convenient technique to study the mechanism of helium embrittlement without irradiation and should provide a rapid screening method to help develop embrittlement-resistant vanadium alloys