Multi-physics and multi-scale methods used in nuclear reactor analysis

• Review of techniques to perform neutronic/thermal–hydraulic coupled calculations.
• Operator-Splitting and Jacobian-Free Newton methods for neutronic/T–H coupling.
• Brief review of pin-power reconstruction techniques used in neutronic calculations.
• Indicative coupled neutronic/T–H calculations with emphasis on the coupling scheme.

In an operating nuclear reactor core, various physical phenomena of different nature are interrelated. Multi-physics calculations that account for the interrelated nature of the neutronic and thermal–hydraulic phenomena are of major importance in reactor safety and design and as a result a special effort is developed within the nuclear engineering scientific community to improve their efficiency and accuracy. In addition, the strongly heterogeneous nature of reactor cores involves phenomena of different scales. The interaction between different scales is a specificity of these systems, since a local perturbation might influence the behavior of the whole core, or a global perturbation can influence the properties of the media on all scales. As a consequence, multi-scale calculations are required in order to take the reactor core multi-scale nature into account. It should be mentioned that the multi-physics nature of a nuclear reactor cannot be separated from the multi-scale one in the framework of computational nuclear engineering as reactor design and safety require computational tools which are able to examine globally the complicated nature of a nuclear reactor in various scales. In this work a global overview of the current status of two-physics (neutronic/thermal–hydraulic) and multi-scale neutronic calculations techniques is presented with reference to their applications in different nuclear reactor concepts. Finally an effort to extract the main remaining challenges in the field of multi-physics and multi-scale calculations is made.