This is mentioned in the material from European Spaceflight.
In 2022, ESA launched the RocketRoll project as part of its program for developing future space technologies. The research was conducted by a consortium led by Tractebel, which included OHB Czechspace, ArianeGroup, Airbus, the French Atomic Energy Commission, as well as the universities of Prague and Stuttgart.
As part of the RocketRoll project, ESA focused on engines that utilize nuclear energy for propulsion. These engines combine high efficiency with a reliable energy source, enabling operation in environments where solar power is unavailable, such as deep space.
The primary objective of the research was to determine the feasibility of creating such engines, identify key technologies, and uncover any economic or technical barriers.
At the end of October, Tractebel announced the completion of the project and presented a plan for Europe to launch a spacecraft with a nuclear engine by 2035.