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


Created in 2019, under the guidance of the Working Party on Scientific Issues of Reactor Systems (WPRS) the expert group will perform specific tasks associated with core thermal-hydraulics aspects of present and future nuclear power systems. Reactor types considered include, but are not limited to, the following:

  • present generation light-water reactors (LWRs) and heavy-water reactors (HWRs);
  • high-temperature reactors (HTRs);
  • sodium cooled fast reactors (SFRs);
  • small modular reactors (SMRs);
  • molten salt reactors (MSRs);
  • fast spectrum systems and other advanced reactor systems.

Coupling issues between core thermal-hydraulics and other aspects considered include, but are not limited to, the following:

  • neutronics
  • fuel performance
  • coolant chemistry
  • structural mechanics


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. Tthe expert group will provide member countries with the guidance and processes for certifying experimental data for its use as a stand-alone core thermal-hydraulic validation or for uses as part of validation pyramid of multi-physics modelling and simulation tools.

The group will provide specific technical information regarding:

  • the status of national and international programmes including experimental capabilities;
  • state-of-the-art reactor core thermal-hydraulics methodologies on different modelling scales;
  • provision of experimental data for model development and validation to the The International Experimental Thermal HYdraulicS (TIETHYS) database;
  • to provide TIETHYS with a methodology for a systematic and standardized 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.

Recent/current activities

Working documents

EGRCTH working area (password protected | reminder)

Meetings, workshops and conferences

Information related to past and upcoming meetings is available in the EGRCTH working area  (password protected | reminder)

OECD Nuclear Energy Agency activities


Tel.: +33 (0)1 73 21 29 00
Deputy Head
Division of Nuclear Science