In recent years the multi-scale modelling approach (MMA) has become increasingly important to complement experiments in the search for new structural materials for nuclear applications such as fusion, accelerated driven system and Gen IV reactors. Multi-scale modelling is also having an increasingly important role in support of the surveillance programmes of currently existing nuclear power plants, as samples of their pressure vessels are becoming rare and their life extension can only be managed via a deeper understanding of radiation damage mechanisms. Within the MMA, ab initio obtained data are generally transferred into interatomic potentials used for large scale molecular dynamics and Monte Carlo simulations of radiation damage production and subsequent microstructural and microchemical evolution. Eventually, the information thereby obtained can be transferred to mesoscopic models, such as other Monte Carlo or rate theory approaches for microstructural and microchemical evolution, or dislocation dynamics, for the description of the plastic behaviour. Finally, a bridge to macro-scales, treated by means of finite element techniques, is built. Results at the meso and macroscopic scales are generally suitable for direct comparison with experimental observations.

Worldwide, a lot of both scattered and co-ordinated work applying an MMA to a number of structural nuclear materials (SNMs) has been carried out in the last couple of decades, with diverse outcomes. In order to define the next steps to be taken towards the development of integrated multi-scale modelling frameworks of practical use for nuclear applications and to enlarge the number of possible contributors to this long-term activity, it is important to provide a critical and complete reference review of the state-of-the-art. This review should highlight weak and strong points of the applied approaches and evidence, as much as possible, to what extent the existing work contributes to enhancing our understanding of radiation damage processes in SNMs and bears the promise of providing, in the future, predictive tools. Based on this review, some conclusions about the priorities in the field should be also drawn.

Objectives

Within the scope stated above, under the guidance of the Nuclear Science Committee (NSC) and under the mandate of the Working Party on Multi-scale Modelling of Fuel and Structural Materials for Nuclear Systems (WPMM), the objective of the Expert Group on Structural Materials Modelling (SMM) is to provide a critical review of the state-of-the-art concerning the use of a MMA to describe the changes induced by irradiation in SNMs.

In more detail, the objectives of the expert group are to:

1. review, based on literature data and direct experience of the experts, significant existing examples of application of the multi-scale modelling approach to SNMs
2. review the existing work on the different SNMs for present and future reactors and on the different issues concerning these materials (see Annex I for an indication)
3. evaluate to what extent the existing work and results bear the promise to come close to the goal of not only reliably reproducing experimental data, but also providing keys for the understanding and interpretation of existing experimental results, with a view, in the long-term, to predicting the behaviour of SNMs under unexplored conditions and/or support the choice and even development of new materials
4. identify, based on the reviews of points 1 and 2, and the evaluation of point 3, the key problems that should be addressed as priorities towards the goal of developing integrated multiscale modelling frameworks of use for structural nuclear materials applications (in terms of physical phenomena to be quantitatively described, materials and materials properties to be addressed, and also modelling techniques to be developed)
5. foster exchange of experience and dissemination of knowledge, e.g. by organising or participating in the organisation of international workshop(s) on the subject (the workshops can be part of existing inititatives)

This expert group is expected to work closely with the WPMM Expert Group on Multi-scale Modelling Methods (EGM3), especially concerning points 4 and 5.