Water-steam thermohydraulics and hydromechanics
Tiret rouge


A water-steam platform specialised in studying thermohydraulic and hydromechanical interactions.​​​​

The purpose of the POSEIDON platform is to improve our understanding of the mechanical and hydraulic behaviour of certain components in a nuclear reactor core and its cooling systems, under both normal and accident conditions. This facility is governed by the French public health code and falls under the supervision of the French nuclear safety authority (ASN). POSEIDON comprises several technological test halls that are unique in the world.
The aim of this facility is to support the design and qualification processes of components, while optimising their performance, reliability, safety levels and service life.
To achieve this, our engineers and researchers have developed various experimental loops to test components, such as to analyse the behaviour of fuel assemblies, control lines or full-scale components from a thermohydraulic and hydromechanical perspective.
Our work also focuses on the issue of vibrations in reduced-scale and full-scale fuel assembly structures, and on the refined characterisation of fluid velocity fields for different flow conditions. We are also studying the thermohydraulic behaviour of the hot pool in sodium-cooled fast reactors (SFRs) in continuous operation, with water used as the fluid to simulate liquid sodium. We also study the deterioration of metal components in contact with coolants in PWR primary and secondary systems, and more specifically the growth, morphology, thickness and composition of deposits on these metal components.
Finally, this platform is used to analyse the levels of wear and corrosion of certain components after testing.

​Activités. © IRESNE/CEA​​


  • Hydromechanics,
  • Thermohydraulics,
  • Fluid-structure interactions,
  • Wear, fatigue, and steam generator clogging using radioactive tracers for monitoring,
  • Qualification of PWR components on a full scale (control rods, assembly guides, fuel assemblies).
​Equipements majeurs. © IRESNE/CEA

Major equipment

Test loops

  • HERMES T and P (full-scale),
  • BIKINI to test components under PWR conditions (320°C, 155 bar),
  • EUDORE (half scale).


  • PLATEAU in water to simulate liquid sodium,
  • COLENTEC loop (steam generator clogging),
  • EVEREST (passive cooling of the whole loop for the NUWARD small modular reactor),
  • THEMIS building (defence project, core thermohydraulics),
  • COLENTEC loop (steam generator clogging),
  • Superclaudia NSSS (30 m3/h, 385°C, 170 bar, 10 m3).
​​Chiffres clés. © IRESNE/CEA​​

​Key figures

5 R&D projects:

  • 50 employees, including 35 permanent-contract staff,
  • 12 R&D projects,
  • €13 million in investment over the past 7 years (2014-2020),
  • Several patents registered.
​​Partenaires. © IRESNE/CEA​​


  • EDF,
  • Framatome,
  • Westinghouse,
  • STXN,
  • Naval Group,
  • TechnicAtome,
  • Rolls-Royce,​
  • KEPCO,
  • Universities of Washington,
  • Universities of Montreal.