The Advanced Thermal-Hydraulic Experiment for Nuclear Analysis (ATHENA) and Safety framework aims to be  the premier international framework for collaborative  thermal-hydraulic (TH) experiments that support nuclear safety analysis for both current and future nuclear power plants (NPPs).

Objective

Its mission is to foster the development, organisation and long-term sustainability of collaborative thermal-hydraulic research capabilities by bringing together a broad, multinational community of stakeholders.

Stakeholders – including regulators, technical support organisations, research institutions, utilities, vendors and academia – will share common goals, resources and results. Framework participants will design, implement and co-ordinate experimental work, as well as cross-cutting activities within TH research, such as counterpart testing, code benchmarking, training, knowledge dissemination and database development. 

ATHENA aims to create the necessary conditions for impactful and sustained research by:

• Identifying and prioritising critical thermal-hydraulic safety research needs;
• Supporting access to and development of scalable experimental infrastructures– both integral and separate-effects facilities– capable of generating high-quality data for validation of state-of-the-art safety analysis codes;
• Facilitating funding mechanisms for joint projects; and,
• Ensuring broad international participation and co-ordination.

Reactor technologies

The framework addresses  thermal-hydraulic code validation and development for a wide range of reactor technologies, including advanced water-cooled reactors (WCRs), small modular reactors (SMRs) and non-WCR systems such as those using alternative coolants (e.g.gas, liquid metal, molten salt).

For advanced WCR designs, ATHENA aims to address systems with both conventional features, such as those found in large-scale PWRs, BWRs, PHWRs and VVERs,and innovative elements, including passive safety systems, extended operational conditions and novel thermal-hydraulic phenomena.

Scope and specifications

Based on the initial recommendations in the NEA Nuclear Safety Research Roadmap, the following focus areas have been identified for ATHENA:

1. TH research for WCRs (including SMRs) on:
   • Reactor coolant systems
   • Containment
2. Broader exploration of knowledge gaps and how to close them, particularly related to non-WCR technologies.

The specifics, which will be defined and prioritised by ATHENA framework members, are below.

1. Core thermal-hydraulic phenomena
   • Thermal-hydraulic processes within the reactor core, including critical transient conditions such as reactivity-initiated accidents (RIA), loss-of-flow accidents, and loss-of-coolant accidents (LOCA)

2. RCS thermal-hydraulics
   • System-wide thermal-hydraulic phenomena across the RCS
   • Coolant stratification and mixing next to reactor vessel inner wall (PTS)
   • Component-specific behaviour, such as performance of steam generators and pumps

3. Integrated RCS-containment interactions
   • Dynamic interactions between the RCS and containment systems and structures.
   • Containment response, containment-specific thermal-hydraulic processes and related phenomena.

5. Innovative components and configurations
   • Thermal-hydraulic behaviour of advanced components (e.g., helical coil steam generators).
   • Non-traditional system configurations, including those supporting emerging non-electric nuclear applications.
6. Cross-cutting topics relevant to WCRs and non-WCRs
   • Multi-physics interactions (e.g., coupling of thermal-hydraulics with neutronics and structural mechanics), including fluid–structure interactions (FSI), and flow-induced vibration (FIV).
   • Gravity-driven and low-pressure transient flows.
   • Boundary condition effects on combustion and explosion risks (e.g., hydrogen combustion, carbon dust hazards).
   • Thermal striping and thermal stratification.
   • Effects of phase change dynamics.
   • Boundary conditions for fission products transport.
   • Thermal-hydraulics in spent fuel pools and large-scale water pools.
   • Performance evaluation and interaction between active and passive safety systems.
   • Others, as identified by ongoing technical needs.