ATLAS 4 project reviews progress and explores complementary research

The NEA ATLAS Phase 4 (ATLAS-4) Joint Project held the third meeting of the Programme Review Group (PRG) and the Management Board (MB) from 15 to 17 April 2026 in Brussels, Belgium. Hosted by Bel V, the meetings brought together experts from research organisations, regulatory bodies, and industry to review progress of the experimental and analytical programme. ATLAS-4 focuses on investigating complex thermal-hydraulic phenomena relevant to the safety of existing and future light-water reactors, including small modular reactors. The project supports the validation and improvement of safety analysis codes through large-scale integral experiments addressing accident and design-extension conditions. During the meetings, participants reviewed the status of the 2026 experimental programme, recent test results, test specifications, and pre-test analyses. Particular attention was given to analytical activities, including forthcoming benchmark exercises and joint analytical workshops, aimed at strengthening the link between experimental data and code validation. The participants confirmed the strategic importance of the project within the NEA framework and its role in supporting international collaboration on nuclear thermal-hydraulic safety research. The meetings concluded with a technical visit to the von Karman Institute for Fluid Dynamics (VKI) on 17 April 2026, offering presentations and laboratory tours covering pool-scale experiments, fuel-assembly-scale studies, fluid-induced vibration (FIV) research, and demonstrations of digital twinning approaches and advanced measurement techniques. Discussions highlighted the strong complementarity between ATLAS integral effect test facilities and VKI’s specialised infrastructures, emphasizing the value of combining large-scale system experiments with targeted separate-effect investigations. This collaboration aims to enhance code validation, reduce uncertainties, and contribute to improved safety assessment methodologies. Participants confirmed the continued progress of ATLAS-4 and its central role in advancing international understanding of safety-relevant thermal-hydraulic phenomena within the NEA nuclear safety research programme.