Suppression of helium clustering in tungsten via dilute vanadium alloying

Helium clustering in W-based plasma-facing materials in fusion reactors critically influences bubble nucleation and irradiation resistance. Using molecular dynamics simulations, we investigate He clustering behaviour in W-V and W-Ta alloys across a temperature range of 300 to 1500 K. While oversized Ta solutes in W-Ta induce increased He clustering at high temperatures, dilute W-V alloys ( < 20 at.% V) exhibit an anomalous inverse relationship whereby the He clustering fraction decreases with increasing temperature. We attribute this to the weak self-trapping due to lattice mismatch and concentration effects. In dilute W-V alloys, the undersized V atoms create local tensile strain that provide energetically favourable lattice locations for He accommodation and weakens the driving force for He self-trapping. Consequently, although He atoms aggregate at room temperature, the clusters are thermally unstable and dissociate at elevated temperatures rather than stabilizing via vacancy formation.