Proceedings of the ITEM workshop on prediction of radiation damage in ferritic alloys: Synergy between multiscale modelling and modellingoriented experiments

The multiscale modelling approach for the prediction of radiation effects in materials is based on the idea of linking different computational models, each dealing with a certain length and time scale. The validity of all of these models needs to be verified experimentally. Validating models used to describe radiation damage at small scales requires the use of refmed advanced experimental techniques, whose output can be difficult to interpret. Some support to their
interpretation can be gained by developing and optimising dedicated numerical tools, capable of reproducing the image or signal that a certain type of microstructural feature will produce when observed with an appropriate experimental technique. In addition, to validate the present models at their current level of development, experiments must be done on simple materials (model alloys of engineering materials), under well controlled conditions. Experiments of this type, where adequate computational tools are used to close the loop between simulation validated by experiment and experiment intepreted with the support of simulation, are called modellingoriented experiments. Only modelling-oriented experiments supported by adequate models, can help discriminate among the fundamental mechanisms responsible for macroscopic radiation effects.
Discussing up to what extent it is currently possible to actually validate simulation results and establish a synergy between multiscale modelling and modelling-oriented experiments, in order to better understand the mechanisms underpinning macroscopic radiation effects, was the motivation for the organisation of the workshop on "Prediction of radiation damage in ferritic
alloys", held on 23-24 October in Mol. This workshop had the ambition of bringing together European experts from two communities, "modellers" and "experimentalists", mostly involved in the ITEM Network, but not only, for a constructive and open debate. Recognised experts from outside the Network were also invited to contribute to the meeting.
The main conclusion is that multiscale models are essential to underpin existing macroscopic embrittlement correlations. Equally essential are theoretical methods to predict the response of experimental techniques to identified microstructural features. Impressive progresses have been achieved in recent years towards the simulation of realistic irradiation conditions and related
hardening effects, as well as in the development of computational techniques dedicated to the interpretation of experiments. Nonetheless, modelling-oriented experiments where a real and thorough comparison between simulation and experiment can be done, thereby creating a double-direction feedback (experiment interpreted in terms of simulation results and simulation results improved by comparison with experiments), remain scarce and difficult to perform. The main reason is that, even in the case of the simplest experiments on model materials, there are still many unknowns (both at the theoretical and experimental levels) that the simulation cannot fully handle.