Helium bubble growth at BCC twist grain boundaries

► We model He bubbles in α-Fe at twist grain boundaries and bulk using MD. ► We study the pressures and volumes of the helium bubbles. ► The pressure of a bubble is lower at the twist boundary than in bulk. ► Interstitial loops are formed in all cases but are trapped at a twist boundary. ► The maximum density for the bubbles is found to be 1.7 He/VacFe.