Missions

The cladding material of fuel rods in nuclear reactors is made up of zirconium alloys whose microstructure evolution under irradiation leads to macroscopic growth. Experiments clearly show that adding niobium into zirconium alloys improves their performance regarding to dimensional stability. Delayed vacancy c loop formation, as well as the formation of niobium enriched nanoprecipitates, have been reported and might explain their enhanced performance. Despite the high amount of research on zirconium alloys, we still don't know why alloys containing Nb perform better with respect to irradiation growth, and how Nb nanoprecipitates affect point defect clustering and irradiation growth.
Several of the Nb precipitates physical properties remain unknown or incomplete: what is their composition and how does it evolve during irradiation? Which stress state is generated by these precipitates? What is their impact on the elimination of the point-defects created by irradiation, i.e. their sink strength? All those questions require a better knowledge of the precipitate shape & distribution, as well as of the nature of their interface with the matrix.

Activities

Therefore, the postdoc will aim to fully model the Nb nanoprecipitates in order to obtain their sink strength and absorption biases, i.e. their capacity to eliminate the vacancies and self-interstitials generated by irradiation. It necessitates first an assessment of the degree of coherency and effective stress-free strain of the Nb nanoprecipitates. Having these kinds of information will help us understand how these precipitates interact with point defects and dislocation loops in the microstructure and provide input data for mesoscale kinetic models of the microstructure evolution under irradiation.
A throughout analysis of the precipitates will encompass atomic scale simulations, relying on classical molecular statics (MS) using an EAM empirical potential for Zr-Nb recently developed at CEA, and on ab initio calculations, pursuing past efforts, as well as continuous elastic modelling and micro-mechanical calculations using a in-house code based on a Fast Fourier Transform (FFT) solver. The numerical results will be compared to high-precision experimental measurements.

Skills

The applicant must hold a valid Ph. D. Degree in Solid State physics or Materials Science, ideally with experience in:
- physical metallurgy,
- continuous elasticity modelling
- micromechanical modelling
- atomistic calculations (ab initio, classical molecular statics, molecular dynamics)

Experience in computer programming is also required.

The applicant must be fluent in English and/or French.

Work Context

This post-doc is part of a joined ANR research project between IJL, CEA, UMET, EdF and Framatome. Strong interaction with the other project partners is expected, specifically to compare the modelled nano-precipitates structure with the one characterized experimentally by transmission electron microscopy, atom probe tomography and X-ray synchrotron diffraction. Interaction with other partners is also expected to use outputs of atomistic simulations in multiscale modelling of kinetic evolution under irradiation. The post-doc will work at IJL under the supervision of Maeva Cottura and Benoît Appolaire in close collaboration with Emmanuel Clouet at CEA Saclay (Paris suburbs). Regular trips to the CEA are to be expected.

Workplace
The project will take place at the Jean Lamour Institute one of the largest French laboratories for material sciences (https://ijl.univ-lorraine.fr/). The institute is part of the CNRS (http://www.cnrs.fr/index.php) and the Université de Lorraine (http://www.univ-lorraine.fr/). The Jean Lamour Institute is in Nancy, a dynamic mid-size city with a population of > 200 000, including about 48000 students and 3700 professors and researchers.

The position is located in a sector under the protection of scientific and technical potential (PPST), and therefore requires, in accordance with the regulations, that your arrival is authorized by the competent authority of the MESR.