In this paper we suggest considering sustainability as a moral framework based on social justice, which can be used to evaluate technological choices. In order to make sustainability applicable to discussions of nuclear energy production and waste management, we focus on three key ethical questions, namely: (i) what should be sustained; (ii) why should we sustain it; and (iii) for whom should we sustain it. This leads us to conceptualize the notion of sustainability as a set of values, including safety, security, environmental benevolence, resource durability, and economic viability of the technology. The practical usefulness of sustainability as a moral framework is highlighted by demonstrating how it is applicable for understanding intergenerational dilemmas—between present and future generations, but also among different future generations—related to nuclear fuel cycles and radioactive waste management.