Expert Group on System Reactor 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 System Reactor 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.