Swelling of solution-treated American Iron and Steel Institute (AISI) 316 L (UNS 531603) was determined by means of transmission electron microscopy (TEM) analysis after dual beam irradiation (300 keV Ni⁺ and 25 keV He⁺ at two different displacement rates and a fixed implantation rate of 120 appm He/dpa. In addition, the fluence dependence of swelling was determined for Ni⁺ irradiation after helium pre-implantation. Data evaluation according to an appropriate void growth model yielded the dislocation bias to be 0.154 ± 0.033. The pre-implantation experiments clearly demonstrated the small bubbles to act as neutral sinks. The small cavities of the bimodal distribution observed after dual beam irradiation therefore reduce the swelling rate. The small cavities were calculated to consist of near equilibrium helium bubbles with a surface energy of 2.2 ± 0.8 N/m. The effective activation enthalpy for nucleation was found to be 2.8 ± 0.3 eV.