The role of impurity oxygen in hydrogen bubble nucleation in tungsten

► A new impurity assistant mechanism of H bubble nucleation is proposed based on the results of O-H-V interaction. ► The interstitial O atom traps multiple H atoms to form O-H complex. ► The initial vacancy could be created at the unstable sites nearby the O-H complex to form stable V-O-H complex. ► Abundant V-O-H complexes could survive due to their lower formation energy and thus the hydrogen bubble nucleates.