Vacuum laser welding was employed to manufacture 80 mm thick welds in SA508 Grade 3 steel in two weld passes, using a 16 kW laser, while travelling at 150 mm/min. The motivation was to explore the potential for the application of the process to the joining of large, safety-critical nuclear components, such as the steam generators or the pressuriser in a pressurised water reactor (PWR). The advantages of vacuum laser welding are first reviewed, and compared to those of electron beam welding, in terms of the process physics. Preliminary development work is then summarised, together with an evaluation of weld quality, mechanical properties and residual stresses. Vacuum laser welding warrants further development, as it offers significant promise for future nuclear build programmes.