The transition to sustainable energy systems is a critical priority for European countries in advancing energy innovation and security. Among the most debated solutions are nuclear technologies, including fusion and next-generation fission power plants, which have the potential to play a significant role in Europe’s energy mix. However, public support for these technologies is complex and influenced by a range of factors, including economic considerations, environmental concerns, and perceived social impacts. To address this gap, we conducted a conjoint experiment designed to assess public support for alternative nuclear energy development plans, fielded among a highly representative sample of the French, German, Italian, British, and Polish populations in March 2025. Respondents are presented with various scenarios that differ across several key dimensions: the source of technological research, the level of international cooperation, the proximity of power plants to residential areas, construction costs, emissions, electricity prices, fuel sourcing, safety monitoring, and workforce composition. This multidimensional conjoint experiment allows us to identify the causal relationship between hypothetical fusion and fission energy development plans and public support or opposition to these technologies. The results reveal that public preferences for nuclear energy development plans, whether for fusion or next-generation fission technologies, are shaped by similar factors. Respondents generally favored plans with lower emissions, domestic fuel production, and cost-effective solutions, regardless of the technology type. While both fusion and fission were regarded as viable options for supporting the energy transition, concerns about high development costs and long timelines negatively affected overall support for both technologies.