The Joint Evaluated Fission and Fusion File (JEFF)  Nuclear Data Library Project is a collaboration between NEA Data Bank participating countries. The JEFF library combines the efforts of its different working groups to produce a common set of evaluated nuclear data, mainly for fission and fusion applications. The JEFF project meets twice a year, in autumn and spring. The next edition of the Nuclear Data Week will take place on 13-17 April 2026, and will host the JEFF Co-ordination Group and will bring together the JEFF technical sessions and the APRENDE (Addressing PRiorities of Evaluated Nuclear Data in Europe) project progress report.

Additionally, this edition also includes a joint session together with the International Criticality Safety Benchmark Evaluation Project (ICSBEP) to enhance the collaboration in terms of benchmarking activities that could benefit future JEFF Nuclear Data Library developments.

Overall, this format aims to strengthen collaboration and build new synergies between the communities contributing to the different areas of the nuclear data pipeline.

Detailed information on the time slots allocated for each technical session can be found in the meeting agenda.

• 2 February: Registration opens.
• 16 March: Draft timetable released.
• 20 March: Registration closes for speakers and onsite participants.
• 31 March: Distribution of detailed agenda.
• 31 March: Registration closes for online audience members.