South Korea is an important case study for understanding the future role of nuclear power in countries with on-going economic growth, and limited renewable energy resources. We compared quantitatively the sustainability of two 'future-mapping' exercises (the 'Governmental' scenario, which relies on fossil fuels, and the Greenpeace scenario, which emphasises renewable energy and excludes nuclear power). The comparison was based on a range of environmental and technological perspectives, and contrasted against two additional nuclear scenarios that instead envisage a dominant role for nuclear energy. Sustainability metrics included energy costs, external costs (greenhouse-gas emissions, air pollutants, land transformation, water consumption and discharge, and safety) and additional costs. The nuclearcentred scenarios yielded the lowest total cost per unit of final energy consumption by 2050 ($14.37 GJ -1 ), whereas the Greenpeace scenario has the highest ($25.36 GJ -1 ). We used probabilistic simulations based on multi-factor distributional sampling of impact and cost metrics to estimate the overlapping likelihoods among scenarios to understand the effect of parameter uncertainty on the integrated recommendations. Our simulation modelling implies that, despite inherent uncertainties, pursuing a large-scale expansion of nuclear-power capacity offers the most sustainable pathway for South Korea, and that adopting a nuclear-free pathway will be more costly and produce more greenhouse-gas emissions.