Multiphysics are simulations using computer applications or software to couple multiple physical events in order to predict or validate the physical real-world outcome.

The nuclear industry has always prioritised the safe, reliable and economically attractive operation of nuclear power reactors. Given these priorities, the development, validation and application of predictive reliable modelling capabilities for both normal and accident conditions has evolved from best-estimate calculations to first principle high-fidelity multi-physics simulations.

Especially important are the multi-physics interactions in reactor cores. In the past, these different interactions were treated either as boundary conditions (i.e. each physics calculation was performed independently and the impact of other physics phenomena were taken into account through boundary conditions) or using very simplistic models for some of the physics phenomena. Examples for the latter are the point kinetics model implemented in system thermal-hydraulic models or one-dimensional thermal-hydraulic models implemented in neutronics core design codes.

Recently, advances in computing power and numerical methods have broadened the appeal of multi-physics simulations, in turn highlighting the need for experiments to validate these simulations.

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NEA work on this topic

A community of multi-physics experts was formed within the Expert Group on System Reactor Multi-physics (EGMUP), and is responsible for advancing multi-physics activities.

Under the EGMUP,  the NEA has undertaken activities aimed at verification and validation of multi-physics tools, and collecting the experimental data that underpins the work. 

Notably, the EGMUP publishes expert guidance in the domain of multiphysics, and work conducted within EGMUP has led to numerous conference and journal publications.