The state has always in multiple ways supported the implementation of nuclear-sector megaprojects. The desirability, legitimacy and sustainability of such support cannot be judged objectively and out of context. Notions used to justify support, such as ‘market distortions’ and ‘market failures’, are ultimately subject to deliberation and negotiation in the historically shaped context of the country in question. Drawing on illustrative case studies of media debates in France and the UK in 1990-2020, and stakeholder interviews conducted in Finland in 2016, this article explores the ways in which country-specific histories and traditions have shaped the discourses on state support for nuclear energy megaprojects since the 1990s, with particular attention to economic subsidies. The malleability of the notions of state support and subsidies has allowed political actors in the three countries to opportunistically adapt their argumentation. Where the nuclear proponents used to rely on economic arguments, today opponents highlight the economic unviability of nuclear, while supporters call for broadening the criteria to the wider benefits of nuclear megaprojects in fostering sustainable development. The analysis shows the solidity and power of the respective country-specific nuclear regimes in reproducing and shaping discourses according to their own needs and agendas. In the UK, successive governments undertook substantial efforts, particularly since 2008, to redefine the long-standing principle that nuclear new-build should not be subsidised. In France, nuclear proponents reproduced an image juxtaposing affordable nuclear with subsidised renewables within a specific French public-sector electricity-sector model of a ‘monopoly that works’. The dominant Finnish discourse portrayed nuclear as an electricity source that needs no subsidies, and supplies cheap and reliable low-carbon baseload electricity necessary for the country’s vital export industry. This article argues that the extensive controversies over nuclear subsidies – such as those in the UK – can attend to the procedural requirements of sustainable development, by improving the social robustness and sustainability of policies, and helping to even out the multiple types of asymmetries of power between nuclear-sector actors.