PurposeHistorical French fleet of Nuclear Power Plants (NPP) is near end-of-life, with 14 NPPs planned to begin decommissioning by 2035. Despite decade-old calls for more research regarding these activities' environmental impact, very few if any studies were conducted since. Due to the French fleet high-degree of standardization, a prospective investigation regarding the Fessenheim NPP-first large-scale plant to be decommissioned in France, starting 2026-is conducted to identify results of interest beyond this case study.MethodsA life cycle assessment is realized, following ISO 14040/44, with a functional unit defined as "the decommissioning of the Fessenheim NPP." The system boundaries encompass four unit-processes: dismantling of electromechanical equipment, clean-up of the structures, demolition of plant buildings, and transport of conventional and radioactive waste (RW). This last unit-process is investigated separately to make a clear comparison of conventional and radioactive waste. Pre-decommissioning activities, soil rehabilitation, and RW final storage are excluded. Primary data were obtained from the decommissioning public report of EDF (Electricity of France), with scaling based on the literature and third-party reports/documents. Background processes were modeled with the ecoinvent 3.8 database. Environmental impacts are estimated using the CML-IA baseline methodology to allow comparison with previous works based on CML2001.Results and discussionThe "Metal cutting" sub-process is found to be the major contributor to environmental impacts during dismantling, clean-up, and demolition, results varying from 62.6 to 99.5% depending on the impact category. A sensitivity analysis explores the effect of variation in shares of thermal and mechanical cutting. It demonstrates the huge potential of impact reduction for the total system under study if thermal cutting use is limited as much as possible. Despite representing only 5% of the total mass of waste, RW scores 1.8-6.6 times higher than conventional waste during transport, due to much higher distances to cover and specific conditioning. Previous explorations of results transferability are found to be methodologically uncertain, and the NPP total power installed is evaluated as an unpromising transferability factor.ConclusionsDecommissioning of nuclear power plants is still in need of thorough studies based on exhaustive and transparent datasets. Until then, state-of-the-art prospective assessments and transferability of LCA results to future studies are severely limited. Restraint in use of oxy-acetylene cutting is nevertheless highly recommended. French unique policy regarding very low-level waste needs further consideration, and decentralized storage sites are a promising research lead.