The Nuclear Energy Agency (NEA) has launched the fourth phase of the Advanced Thermal-Hydraulic Test Loop for Accident Simulation (ATLAS) project, continuing its mission to address critical thermal-hydraulic safety issues in light water reactors (LWRs). The project aims to deepen international understanding of complex accident scenarios and to further improve simulation code validation through large-scale integral effect tests (IETs) conducted at the ATLAS facility in Korea.
The kick-off meeting for ATLAS Phase 4 was held at NEA headquarters in Boulogne-Billancourt, France, from 23 to 25 April 2025. The event gathered 42 participants, including 13 remote attendees, representing 20 organisations across 10 countries. Over a span of four years, from January 2025 to December 2028, the project will feature ten IETs.
Building on the lessons learnt from previous phases and the post-Fukushima Daiichi emphasis on passive safety systems, the ATLAS Phase 4 programme targets five thematic research areas:
- interaction phenomena between the reactor coolant system and containment;
- performance evaluation of passive safety systems;
- effects of natural circulation;
- assessment of design extension conditions; and
- counterpart testing.
These tests will address outstanding challenges related to low driving forces, asymmetric flow behaviours, thermal-hydraulic instabilities, and the validation of passive systems under realistic accident conditions.
The NEA technical secretariat played a key role in facilitating the co-ordination and launch of this collaborative research effort. By bringing together regulators, research organisations, and nuclear industry experts, ATLAS Phase 4 will continue to enhance collective understanding of safety-relevant thermal-hydraulic phenomena and contribute to the refinement of advanced safety analysis codes.
More information on the ATLAS project and NEA joint projects is available here.
