Sub-programme 4 Pilot Projects

ICAR Pilot Project

The influence of initial microstructure/carbon distribution to the swelling and hardening of irradiated FeCrxC alloys.

Ferritic/martensitic high-Cr steels are candidate structural materials for the construction of several components of GEN IV reactors, because they are expected to be more resistant to irradiation, while offering good thermal and thermal-mechanical properties. To date, the perception on the role that the different alloying elements and their amount have on the mechanical performance of these steels under irradiation is limited. One of the main parameters which are responsible for the variation of the alloy microstructure and defect properties after irradiation is dissolved carbon distribution. Carbon easily segregates at dislocations and grain boundaries as well as it binds to neutron irradiation induced defects such as vacancy and interstitial clusters and precipitates. In this project we aim to study the influence of initial microstructure and carbon distribution to the defect properties formed after neutron, proton and ion irradiation. By focusing on the synergy between carbon, vacancy, self-interstitial, and chromium solute atoms in the clusters, defects will be fully characterized as well as their influence to the macroscopic physical properties of the alloys such as swelling and hardening.

IOANIS Pilot Project

Ion irradiation as a neutron irradiation surrogate – Potential, challenges and limits.

The development and qualification of new structural materials for future nuclear applications like GEN IV fission and fusion reactors rely on comprehensive irradiation experiments with prototypic irradiation conditions. The limited availability of suitable neutron irradiation facilities as well as costs and time expenditure of neutron irradiation experiments give rise to an interest in alternative irradiation sources, e.g. ion irradiation. However, by using a surrogate for neutron irradiation a transferability issue is introduced. The project is aimed at exploring how PIE results for ion-irradiated f/m Cr steels can be transferred to neutron irradiation, identifying the limits of ions as a neutron irradiation surrogate and developing strategies to obtain equivalent experimental information for ion-irradiated and neutron-irradiated material. The project will include systematic ion irradiation experiments on Fe-Cr model alloys and f/m Cr steels addressing selected transferability issues and recently found differences between the irradiation response of self-ion and neutron irradiations in Fe-Cr model alloys. The experimental activities will be accompanied by modelling.

MARACAS Pilot Project

Simulation of Model Alloys Representative of AustenitiC stAinless Steel.

This pilot project aims at better understanding the microstructural evolution of austenitic stainless steels at low irradiation doses. Such alloys will be used in GenIV prototypes (e.g. ASTRID) for both structures (316 L(N) steels) and cladding (AIM1-type steels). It is therefore important to understand their evolution under irradiation, notably for the 60-year design life demonstration.Model alloys will be investigated both theoretically and experimentally, in order to simplify the problem and build physical models based on atomistic calculations. Two main aspects will be considered. First, thermodynamic and kinetic models for NiCr and FeNiCr will be built in order to describe accurately their phase diagrams and the kinetics of segregation and ordering. Atom Probe Tomography (APT) experiments will be done to assess the validity of these models. Secondly, the effect of Ti and C will be studied in Ni. These two impurities are known to modify appreciably the microstructural evolution in AIM1 steels and notably the dislocation evolution that occurs in the incubation regime before the onset of swelling. Several hypotheses could explain this phenomenon, and one of the objectives of this work is precisely to gain more clues about the key mechanisms. For this purpose, a combination of kinetic modelling and experiments (Transmission Electron Microscopy – TEM – and APT) will be used.

MEFISTO Pilot Project

Modelling of embrittling features in irradiated F/M steels and alloys.

The main objective of the MEFISTO PP is to build knowledge on the effect of the composition on the type of phases that form under irradiation in high-Cr F/M alloys, their kinetics of formation, their effect on radiation-hardening (generally correlated with embrittlement), as a basis for mechanistic embrittlement correlations. More specifically, the work will address two issues:

Study of the mechanism of formation of Cr-rich-NiSiP clusters, including a detailed description of the mechanisms of diffusion of the constituent chemical elements in Fe alloys, their possible role as precursors for complex phase formation, and their impact on radiation-induced hardening, using atomic and dislocation-level simulation tools.
Design and performance of modelling oriented experiments on model alloys FeCr(NiSiP) and, possibly, steels, in order to obtain detailed information on the Cr-rich-NiSiP clusters and their effect on radiation-induced hardening, thereby allowing the improvement and validation of the models, as well as setting the basis for the derivation of mechanistic embrittlement correlations.

These two issues are intimately correlated, as experiments provide information to develop models and models are used to rationalise experimental results.

MOIRA Pilot Project

Modelling of irradiation creep in F/M alloys.

The main objective of the MOIRA PP is to develop and then apply atomic- and dislocation-level simulation tools to evaluate the relative importance of irradiation creep mechanisms, such as: stress-induced preferential absorption (SIPA) or nucleation (SIPN), anisotropic diffusion, dislocation climb&glide (deriving relevant dislocation mobility laws), slip bands. This will be done by:

Studying atomistically the absorption of defects at dislocation loops and lines under given stress fields and the influence of the latter on stability and mobility of radiation defects.
Using continuum viscoplasticity modelling coupled to lower scale models to determine the effect on (visco)plasticity of dislocation climb.

MOLECOS Pilot Project

Modelling of heavy-liquidmetal Corrosion of Steels (SP1/SP4).

The objective of this project is to obtain a basic understanding of the processes involved in the corrosion of steels by molten lead and lead bismuth. Corrosion represents a critical challenge in the use of heavy liquid metals (HLM) as coolants for the realization of Gen IV reactors and concentrated solar power systems. A controlled surface oxidation (Active Oxygen Control, AOC), obtained maintaining a low concentration of oxygen in the molten metal, has proven to be an effective mean to promote the formation of a self-healing oxide film on the steels surface, so reducing steel corrosion and coolant contamination. On the other hand it has been shown that above temperatures around 450~500°C, depending on the steel considered and on the experimental conditions, the technique is not effective and severe corrosion attacks are observed. The development of a chromium rich oxide layer on the steel surface, that acts as physical barrier to further oxidation in most environments, is not effective in HLM at high temperature. The feature responsible for the increased corrosion rate is an unusual oxygen diffusivity trough the oxide scale, whose mechanism is still not understood. A research line that received little or no attention by the research community is that the enhanced corrosion observed at high temperatures in those environments can be associated with the chemical interaction of the steels with the coolants and the formation of complex oxides. Phase transitions in the complex oxide system leading to the formation of defective structures, permeable to oxygen, or low melting compounds, can account for the enhanced oxygen diffusion and enhanced corrosion. In order to investigate this promising hypothesis, a detailed knowledge of the relevant part of the phase diagram of the complex system under study and more accurate microstructural investigations are needed. The main obstacle is the lack of a database of thermo-chemical and structural data. To try to fill this lack of knowledge, targeted corrosion experiments carried out with an accurate control of the chemistry and advanced characterization techniques, coupled with a computational approach are proposed. In particular, the theoretical approach will contribute to estimate thermo-chemical data, not available in literature, useful to evaluate the composition at thermodynamic equilibrium of the system, by means of codes based on the minimization of the Gibbs free energy. The chemical interaction of the steels with the coolants and impurities, due to dissolution processes or introduced for conditioning purposes, plays a key role also in the implementation of the AOC coolant chemistry control systems. Atomistic modelling will be used to gain important information about the solubility and diffusion data, fundamental to understand the interaction of dissolved metallic impurities (Fe, Ni, Cr, Mn) with oxygen and hydrogen in the HLM.

MOSEL Pilot Project

Modelling Steel Embrittlement by heavy Liquid metals (SP1/SP4).

The objective of this Pilot Project Proposal is to contribute to the comprehension of the physics and the microstructure evolution governing the liquid metal embrittlement of steels exposed to heavy liquid metals. LME refers to various different phenomena that take place when a ductile metal in contact with a liquid metal shows an unusual and unpredictable brittle behaviour if stressed in tension, compared with the tensile behaviour in air. LME occurs in a wide range of specific solid-liquid metal combinations and is strongly affected by the chemical compositions of the solid and liquid metals. A large amount of experimental data from mechanical testing in liquid lead alloys and, to a smaller extent, in pure lead environments has been obtained during the last decades in the context of the former FP7, FP5 and FP6 projects and in support of the MEGAPIE international initiative. Ferritic/martensitic steels are reported to suffer from this issue, and thanks to the extensive work done, the features of the phenomenon are at least qualitatively delineated. However a clear understanding of the mechanisms behind HLM LME is still missing as well as a model to rationalize the whole body of experimental data. Austenitic steels seem to be much less affected by this issue, at least at temperatures below 400°C, nonetheless as demonstrated in the FP7 MATTER project, the use of some type of filler material to reduce the susceptibility to hot cracking, can lead to a delta ferrite contents up to 5% in the welds. LME could have a serious impact on the mechanical properties of welded joints of austenitic steels exposed to HLM. The role of unstable austenite having a martensitic transformation under mechanical strain is also a possibility that would render austenitic steels more susceptible to LME. It is widely recognized that the main source of uncertainty is related to the complexity of the phenomenon and to the difficulties in controlling the experimental details that make difficult to discriminate the processes relevant to LME from those that are not.

NINA Pilot Project

Development and applicaton of nanoindentation (SP1/SP2/SP4).

The aim of this pilot project is to bring together expert groups working on nanoindentation to develop common methods and procedures to address issues of nuclear related materials. Nanoindentation is applied or planned to apply in research activities (pilot projects) under different subprograms of EERA JPNM therefore common procedures, understanding and exploitation of the method is essential. Particularly high temperature indentation is of interest for witch standard does not exist. Furthermore the project aims to develop good practice guidelines and addresses the application of the method for:

investigating homogeneity and anisotropy of nuclear related materials;
investigating irradiation effects (both neutron and ion) on microstructure and nanomechanical properties;
quantifying stress state, dislocation density and dynamics.

SLIPLOC Pilot Project

Multiscale approach for shear localization.

This project aims at predicting deformation localization occurring during tensile or cyclic loading of pre-irradiated steels. The project concerns the main steels used in fission reactors of all generations (ferritic-martensitic and austenitic stainless steels). A multiscale modelling approach is applied to predict slip localization features and consequences in terms of mechanical damage (necking, intergranular damage occurring in both inert and corrosive environments). At the lowest scale, molecular dynamics will allow a fine characterization of dislocation – irradiation defects interactions, completing the existing results, as well as the evaluation of radiation-induced loop and chemical segregation around dislocation lines. Discrete Dislocation Dynamics computations together with a continuum modelling based on dislocation and defect evolution equations will be carried out to predict the formation of clear bands and the induced slip localization. Finally, higher scale modelling based on non-convex potentials, polycrystalline homogenisation, necking theory or grain boundary fracture criteria will permit the prediction of the macroscopic behaviour of the pre-irradiated steels and how slip localization leads to damage and fracture. Each computation level provides inputs used at the higher level. And each modelling will be assessed thoroughly by various experimental observations and measurements carried out at the corresponding scale.Tomography atom probe (TAP), in-situ TEM, TEM as well as SEM and Electron Back Scattered Diffraction (EBSD) will be used.