Expert Group on Reactor Systems Multi-Physics (EGMUP)
Reactor installation containment area (vessel). Photo: US Nuclear Regulatory Commission


Under the guidance of the Working Party on Scientific Issues and Uncertainty Analysis of Reactor Systems (WPRS), the Expert Group on Reactor Systems Multi-Physics (EGMUP) advances the state of the art in establishing processes and procedures for certifying experimental data and benchmarking multi-physics multi-scale modelling and simulation (M&S). Coupled behaviours of two or more of the following physics will include, but are not limited to the following:

  • reactor physics
  • thermal-hydraulics
  • fuel performance
  • structural mechanics
  • materials chemistry

Multi-physics aspects of both steady-state and transients conditions of existing and advanced nuclear systems are examined along with uncertainty quantification and propagation through different scale (multi-scale M&S) and different physics phenomena (multi-physics M&S).


The expert group provides recommendations to the WPRS  and the nuclear community on the scientific development needs (data and methods, validation experiments, scenario studies) for multi-physics and multi-scale M&S, including sensitivity and uncertainty methodology for analysis of different reactor systems and scenarios. Guidance and processes to certify experimental data for multi-physics multi-scale M&S and to apply this data to the benchmarking of models will be developed.

To fulfil the above the expert group will provide the following:

  • Standardised benchmark models with detailed uncertainty evaluations and uncertainty a methodology guidelines;
  • Guidance on best practices to combine high fidelity and low fidelity simulation tools;
  • A framework and consensus recommendations for validating multi-physics simulations;
  • Sensitivity and uncertainty methods to facilitate quantification and ranking of coupled physics;
  • Evaluation methods for uncertainty impacts of the following parameters on multi-physics simulations:
    • data (e.g. geometry, materials);
    • numerical methods;
    • physical models;
  • Training opportunities to demonstrate validation principles and practices; and
  • Demonstrations of the validation recommendations for specific applications.

To support its activities, the group will collect and evaluate multi-physics data from available integral facilities and Nuclear Power Plant (NPP) experimental data.  Analytical and numerical benchmarking will also be used to fulfil the objectives.


EGMUP Organisation

Chair Timothy E. VALENTINE (USA)
Vice-Chair Evgeny IVANOV (FR)

All NEA member countries  EGMUP members' working area

Full participant European Commission (under the NEA Statute)

Observer (international organisation)

International Atomic Energy Agency (by agreement)


Mandate: NEA/NSC/WPRS/DOC(2021)2


NEA Secretariat: Oliver Buss


Meetings, Workshops and Conferences

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


Members' working area

EGMUP members' working area (password protected | reminder)

Related news
Publications and reports
Working Party Structure

Click on elements in graph above to jump directly to a specific WPRS or EGMUP activity.