This paper explores the construction of a nuclear power facility at Fessenheim, Alsace, and its role in the remaking of French-German post-war relations and the consolidation of the post-war peacebuilding process. The siting and materiality of nuclear energy technology, I argue, was a key component of the top-down peace-building strategy that guided reconciliation processes at the national and regional levels. This study analyses archival documents, newspapers' articles, interviews with Alsatian antinuclear activists, and amateur films in order to reconstruct how the site for a joint nuclear power plant at Fessenheim was chosen and how it affected cross-border interactions. Although the planning of a French-German nuclear facility at Fessenheim embodied the appeasement that characterised post-war relations at a governmental level between the two nations, its construction had limited impact on the regional reconciliation processes. However, the site of the nuclear plant became central for reconciliation in ways that industry planners did not foresee: opposition to the nuclearization of the Upper Rhine Valley became the driving force for the cross-border reconciliation process. This grassroots mobilisation against the presence of nuclear technology formed the nexus for transcending the legacy of World War II through cooperation toward a common, anti-nuclear future.