This paper explores two places usually left off nuclear maps: Madagascar and Gabon, where the French mined and processed uranium ore, starting in the 1950s. It analyses how the ‘rupture-talks’ of nuclearity and decolonization became intertwined, first by examining the production of these rupture-talks by French expatriates, then by exploring how sociotechnical practices at each site both belied and performed claims to rupture for Malagasy and Gabonese mineworkers. Rupturetalk had material effects: it was inscribed in sociotechnical practice, it involved staking claims to power, and it created expectations among both ¥elites and non¥ elites. Sociotechnical practices ‘conjugated’ colonial power relations, creating real and imagined technological futures in which nuclearity and decolonization confronted and shaped one another. Drawing on the insights and methods of postcolonial studies, this paper argues that focusing on uranium mining in Africa reveals the power effects of creating and maintaining the ontological categories of the nuclear age.