Expert Group on Reactor Core Thermal-Hydraulics and Mechanics (EGTHM)


Under the guidance of the Working Party on Scientific Issues and Uncertainty Analysis of Reactor Systems (WPRS), the Expert Group on Reactor Core Thermal-hydraulics and Mechanics will perform specific tasks associated with multi-scale core thermal-hydraulics and mechanics of present and future nuclear power systems with focus on multi-phase flow heat transfer mechanisms. Coupling aspects of fluid structural mechanical interactions for normal and/or deformed core configurations will be considered, as will problems requiring high fidelity multi-scale core simulation.  The considered reactor systems for which core thermo-hydraulic and structural mechanical issues will be studied include but are not limited to:

  • current fleet of light-water and heavy water reactor cores (LWRs/HWRs) as well as present generation of fuel assembly designs;
  • evolutionary and innovative LWRs/HWRs core- and fuel assembly designs;
  • next generation of core and fuel assembly designsincluding water cooled small modular reactors (SMRs),micro-reactors , high temperature gas cooled reactors (HTGR) as well as advanced fast spectrum systems including sodium fast reactors (SFRs) and molten salt reactor systems (MSRs);
  • high-temperature gas reactors (HTGRs);
  • molten salt reactors (MSRs) and other advanced nuclear systems.


The ojective is to provide expert advice to the WPRS and the nuclear community on the development needs (data and methods, validation experiments, scenario studies) for multi-scale core thermal-hydraulics modelling and simulation of existing and proposed nuclear reactor systems.

A key activity associated with this objective is the identification and preservation of appropriate experimental data. In addition, the EGTHM will provide member countries with guidance and processes for certifying the experimental data for its use as a stand-alone core thermal-hydraulic validation or coupled thermal-hydraulics and structural mechanics. The role of thermal-hydraulics as part of validation pyramid of multi-physics modelling and simulation tools will be done in close collaboration with the Expert Group on Reactor System MUlti-Physics (EGMUP).

EGTHM will provide specific technical information regarding:

  • the status of national and international programmes on reactor core thermal-hydraulics including experimental capabilities;
  • the state-of-the-art reactor core thermal-hydraulics methodologies on different modelling scales;
  • the provision of experimental data for model development and validation to the International Experimental Thermal HYdraulicS (TIETHYS) database;
  • to provide TIETHYS with a methodology for a systematic and standardised process for collecting facility hardware and experimental test data;
  • techniques for high to low fidelity/resolution model data exchange (Hi2Lo);
  • values and distributions of local safety-related parameters and margins.

The expert group will monitor, steer and support the continued development of the TIETHYS database. The expert group also will facilitate the dissemination of technical information and knowledge through activities such as workshops, benchmark studies and training activities.


EGTHM Organisation


Alessandro Petruzzi (ITA)

Maria N. Avramova (USA)


All NEA member countries  EGTHM members' working area

Full participant European Commission (under the NEA Statute)

Observer (international organisation)

International Atomic Energy Agency (by agreement)



NEA Secretariat: Oliver Buss


Meetings, Workshops and Conferences

WPRS and associated Expert Group meetings are held approximately every twelve months. 


Members' working area

EGTHM members' working area (password protected | reminder)

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Publications and reports
Working Party Structure