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PhD Thesis subject: modeling the primary damage to the evolution of the microstructure under irradia

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General information

Reference : UMR8207-CHABEC-002
Date of publication : Thursday, July 18, 2019
Scientific Responsible name : The thesis will be supervised by Charlotte Becquart, professor at the National School of Chemistry of Lille, which belongs to the laboratory UMET (Materials and Transformations Unit) located in Villeneuve d'Ascq and Christophe Domain, EDF engineer in Moret sur Loing
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 1 October 2019
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly

Description of the thesis topic

Prediction of the macroscopic properties of materials often requires a certain amount of atomic scale data. In the context of materials for nuclear reactors, these data are among others the primary damage, that is to say the set of defects created during the interaction of an energetic particle such as a neutron or an ion with the atoms of the material. The energetic particle will interact with the electrons and nuclei of the target atoms. This interaction depends on the mass, charge and energy of the incident particle as well as the characteristics of the target. During this event, the affected nucleus can transmute: there will be, in this case, creation of a new element. It also receives a certain amount of kinetic energy. If this energy is high enough for the atom to leave its atomic site, it will collide with the atoms of its neighborhood. These can in turn acquire enough kinetic energy to produce new collisions. This phenomenon occurring step by step (the phenomenon on the atomic scale is comparable to the shocks between billiard balls), triggers, thus, an avalanche of atomic displacements called "displacement cascades or collisions cascades" see for example
The duration and the size of the cascade, and consequently the number of defects produced, depend essentially on the characteristics of the first atom displaced, commonly called Primary Knock-on Atom (PKA) and the structure of the irradiated metal. The elementary mechanisms that cause radiation damage cannot be systematically observed by experimental techniques because of their very short lifetime (a few picoseconds), and their small spatial extent (between a few angstroms and a few hundred angstroms). A better understanding of radiation damage therefore implies the joint development of modeling and experimental microstructure characterization techniques. This thesis is part of the development of modeling techniques and more specifically on a better description of primary damage and its evolution. To do so, it is necessary to develop interatomic potentials representative of the materials studied. These potentials are generally good enough to represent the material at equilibrium. It is also well known that very short-range interactions corresponding to in extreme compression in solids are well reproduced using Coulomb models and Coulomb models. However, there is no established methodology for the extension of these potentials for intermediate distances, i.e. to make the link between extreme compression and equilibrium while this part intervenes during the displacement cascades and has a great influence on the formation of defects (their numbers and their distributions). It is therefore important to establish a method for constructing this intermediate part for a reliable modeling of the primary damage. This is the first part of the thesis. To do this, the PhD student will, on the one hand, rely on the results obtained in the laboratory recently on the characterization of different properties of potentials and the correlation between these properties and the damage obtained. On the other hand, he/she will use results of first principles or “ab initio” calculations.
In a second step, displacement cascades will be simulated using molecular dynamics to obtain the "source term" allowing to model the evolution of the primary damage created by neutrons but also by ions in defects of larger sizes, comparable with experimental results. For this purpose, the distributions of PKA produced by ions and neutrons will be calculated with the softwares SRIM and SPECTER, and the evolution of the primary damage modeled by our kinetic Monte Carlo code LAKIMOCA. To obtain representative results including rare events, a large number of simulations will have to be analyzed, which will require the implementation of large data processing methods (statistics and big data), with, if necessary, the use of machine learning tools.

The materials targeted will be iron for the method because there exist many potentials for Fe and this material has been extensively studied, then Ni and in the longer term NiCr considered as a simplified but representative material of austenitic materials used in reactors.

Work Context

Context of this work:
This work is part of a structuring project “Ions / neutrons” conducted within a national program including the CNRS and nuclear partners in France (CEA, EDF, FRAMATOME ....) to compare the effect of irradiation with ions and with neutrons in materials but also in the framework of European projects such as SOTERIA ( its follow-up programs and the programs of eurofusion. In parallel with this modeling work, and within the framework of the “Ions / neutrons” structuring project, experimental studies are planned, based on the use of positron annihilation spectroscopy (PAS) and resistivity annealing (RR) r to probe the damage in metals irradiated with ions. In the next 2 years the implementation of the resistivity annealing device (RR) at the CEMHTI laboratory in Orléans will be finalized. Measurements will be made on iron in a first step to compare the results obtained with published studies and qualify the device. Then, in order to get closer to commercial austenitic materials used in reactors (316 for example), the damage induced in metals of CFC structure such as Ni and NiCr will be characterized by the two complementary techniques RR and PAS.
The comparison of the simulation results obtained in the thesis proposed here, with experimental results obtained with RR and PAS will also be done in collaboration with the Royal Institute of Technology (KTH) in Stockholm where a thesis on the modeling of the positron signal and the resistivity of the point defects and their clusters is ongoing. The interactions between the two theses will be intensified by exchanges: each student will make one or more stays in the laboratory of the other.
Supervision and place of the thesis:
The student will join the metallurgy team of UMET ( laboratory located in Villeneuve d'Ascq, near Lille, in the north of France. UMET is made up of about 80 CNRS researchers and researchers, about forty administrative and research support staff, about sixty PhD students, and about fifteen contract researchers and emeritus professors. UMET develops a research focused on the science of materials in fields of diversified applications that can aim at a direct industrial application or the understanding of elementary processes. The metallurgy team has been working with EDF for more than 20 years and is involved in many European projects related to irradiation damage modeling.
The thesis will be supervised by Charlotte Becquart, professor at the National School of Chemistry of Lille, which belongs to the laboratory UMET (Materials and Transformations Unit) located in Villeneuve d'Ascq and Christophe Domain, EDF engineer in Moret sur Loing; with interactions with Marie France Barthe (CEMHTI, Orléans), Pär Olsson (KTH, Sweden) and Gilles Adjanor (EDF R&D).
Charlotte Becquart and Christophe Domain have been working for more than 20 years on the modeling of radiation damage at the atomic and mesoscopic scales. They use and develop simulation means for the atomic scale study of deformation phenomena, phase changes, irradiation damage, etc. The applied techniques are Molecular Dynamics (MD), Monte Carlo methods (MC) and methods of electronic structure calculations using the first principles ("ab initio" methods).
Representative publications of C. Becquart and C. Domain concerning the subject of the thesis: “Influence of the interatomic potentials on Molecular Dynamics simulations of displacement cascades”, C.S. Becquart, C. Domain, A. Legris & J.C. van Duysen, Jour. Nucl. Mater 280 (2000) 73.
“Ab initio threshold displacement energies in iron”, P. Olsson, C.S. Becquart & C. Domain, Mater. Res. Lett. 4 (2016) 219
“An empirical potential for simulating vacancy clusters in tungsten” D. R. Mason, D. Nguyen-Manh & C. S. Becquart, Jour. Phys. Cond. Matter. 50 (2017) 505501.

Additional Information

Required skills
This interdisciplinary subject is intended for students motivated by the numerical simulation of materials (atomic and mesoscopic scale). The candidate must hold an engineering degree and / or a master's degree.
The position requires solid knowledge in materials science and crystallography, good oral and written communication skills to present at conferences and write articles in scientific journals. We are looking for a young researcher who will be involved in his project, curious, with a certain autonomy and a strong motivation to develop modeling skills in the field of metallic materials. In addition, the candidate must be able to work in a team on multidisciplinary projects. The candidate must also have knowledge of programming and notions of linux.

Applications should include a detailed CV; at least two references (people likely to be contacted); a cover letter of one page; a one-page summary of the master thesis; the grades of Master 1 or 2 or engineering school.


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