Recognized but displaced: Uranium mill tailings and the sustainability accounting of nuclear energy

Nuclear-energy sustainability is usually debated through reactor performance, carbon intensity, fuel availability, operational safety and spent-fuel disposal. Less visible are the front-end residues generated by uranium production, especially uranium mill tailings (UMT), likely the nuclear fuel cycle's largest long-lived radioactive residue stream by volume. This Perspective argues that UMT are not merely neglected; they are recognized and displaced through nested governance boundaries. It develops the concept of volume-based leniency and identifies three linked mechanisms: classification displacement, infrastructural pragmatism and sustainability-accounting displacement. Historical regulation, current naturally occurring radioactive material (NORM) and remediation frameworks, the Wismut programme, written clarifications from Nordic radiation-safety authorities, and uranium-mining legacies show how competent institutions can each address a bounded part of the problem without assembling the long-term radioactive, chemical, ecological, financial and distributive liability as a whole. The resulting issue is not whether all tailings should be reclassified as conventional radioactive waste. It is whether nuclear-energy sustainability can be judged credibly when front-end liabilities remain outside, or only weakly attached to, the system boundary used to assess the electricity they enable. Whole-system accounting should not predetermine whether nuclear energy is sustainable; it should ensure that the judgement is made with its material liabilities inside the boundary of analysis. Uranium mill tailings illustrate how a recognized, long-lasting material liability can be displaced through nested governance boundaries. Specialist regimes can reduce impacts and achieve partial administrative closure, while the underlying inventory and stewardship obligations persist. Whole-system nuclear sustainability assessment should therefore keep front-end uranium liabilities within the accounting boundary. • Uranium mill tailings are recognized yet displaced from sustainability accounting. • Volume-based leniency captures special governance of enormous, low-activity residues. • Nested governance boundaries allow partial closure while liabilities persist. • Wismut shows remediation success can still require continuing stewardship. • Whole-system nuclear sustainability should include front-end uranium liabilities.