ATLAS-4 meeting participants at Bel V
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 and to discuss forthcoming activities.
ATLAS‑4 is the fourth phase of the Advanced Thermal‑Hydraulic Test Loop for Accident Simulation (ATLAS) project and focuses on the investigation of complex thermal‑hydraulic phenomena relevant to the safety of existing and future light‑water reactors, including small modular reactors. Building on the outcomes of previous phases, 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 and discussed 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 highlighted 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 participants the opportunity to explore complementary experimental capabilities relevant to nuclear thermal‑hydraulics and fluid‑structure interaction research.
The visit included presentations and laboratory tours covering pool‑scale experiments, fuel‑assembly‑scale studies and fluid‑induced vibration (FIV) research, as well as demonstrations of digital twinning approaches and advanced measurement techniques.
Participants at the MYRRHA Basic SEt-up for Liquid fLow Experiments (MYRRHABELLE) facility at VKI, 1/5‑scale Plexiglas water model of the MYRRHA research reactor primary circuit
Discussions highlighted the strong complementarity between the ATLAS integral effect test facilities and VKI’s specialised infrastructures, underlining the value of combining large‑scale system experiments with targeted separate‑effect investigations. The visit supported exchanges on how integrated experimental programmes can enhance code validation, reduce uncertainties and contribute to improved safety assessment methodologies.
Together, the 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.
ATLAS-4 meeting participants at VKI
