PhD student (M/F) in the Physical Chemistry of Nuclear Materials

Job Description

Thesis Subject

Title: Study of the properties of irradiation-induced defects and their interactions with alloying elements in model austenitic steel materials.
Context:
Nuclear energy is a key component of France's energy transition strategy. This strategy involves the construction of new power plants and the extended operation of existing reactors up to 60 years or beyond. Extending the operational lifetime of reactors offers the advantage of reducing operational costs but requires modifications to operating conditions. Similarly, the increasing production of electricity from solar and wind energy demands greater flexibility in reactor operations. These new conditions necessitate, among other things, the study of the effects of neutron flux variations on the properties of reactor materials. In particular, it will be essential to ensure that non-replaceable components, such as the reactor vessel, continue to meet the design requirements to guarantee long-term safety.
Metallic materials are crucial for the design of fission nuclear reactors, particularly austenitic steels used as structural materials. In these extreme environments, numerous defects such as vacancies, interstitials, and dislocation loops are created in the materials. These defects strongly influence their mechanical and electrical properties. A detailed understanding of these defects is essential for predicting the long-term behavior of alloys and optimizing their in-service performance.
Positron annihilation spectroscopy (PAS) and electrical resistivity measurements are two complementary methods particularly sensitive to the presence of point defects and their evolution after irradiation or thermal annealing.
Objective:
The goal of the thesis is to study the properties of irradiation-induced defects and their interactions with alloying elements in model austenitic steel materials. This involves characterizing point defects and vacancy clusters created by irradiation in Ni-based metallic alloys (Ni-Cr, Fe, etc.) using resistivity and PAS measurements, and correlating the results of these measurements performed on the same samples. We also plan to study the evolution of these defects as a function of thermal treatment (annealing) and/or irradiation dose, and to attempt to establish a correlation model between the types of defects detected and the variation in resistivity.
This experimental work will be carried out in collaboration with theorists within the framework of the PEPR SCIAM "Upstream Nuclear Sciences" project. The experimental results can thus be compared with OKMC (Object Kinetic Monte Carlo) calculations, which will help optimize the parameterization of source terms in the models.
The PhD student will be trained in sample preparation (polishing, annealing) and the characterization techniques mentioned above. He/She will participate in irradiations and electrical resistivity measurements as a function of temperature using the four-point method, as well as positron annihilation spectroscopy measurements performed with the positron accelerator using Doppler broadening spectrometry. He/She will process the data and compare it with the literature.

Your Work Environment

The CEMHTI (Extreme Conditions for Materials: High Temperature and Irradiation) is a CNRS research unit with two sites (High Temperature and Cyclotron), bringing together around a hundred people. The laboratory develops unique expertise and tools at both national and international levels to study, among other things, the physicochemical properties of materials under extreme conditions.
The Researcher (M/F) will be assigned to the Defects, Impurities, Interfaces, Irradiation (DEFI3R) team. He/She will have access to the particle beam facilities of the Particle Beams Platform [1], including:
(i) The Pelletron accelerator, which generates ion beams (0.5–3 MeV) to create defects through atomic displacements and enables in-situ online electrical resistivity measurements in materials, as well as analyses such as RBS (Rutherford Backscattering Spectrometry) and NRA (Nuclear Reaction Analysis).
(ii) A slow positron accelerator, which allows for depth-profile detection of positron annihilation signatures due to vacancy-type defects.
To complement irradiation conditions, the EMIR&A platform may be used, particularly the Jannus Saclay platform. For additional characterization, the researcher will have access to the MACLE platform tools located on the Orléans campus (TEM, SEM/EDX, EBSD, FIB), and will collaborate with:
The IRCER laboratory (Limoges) for XRD (X-Ray Diffraction) measurements.
The GEMAC laboratory (Versailles) for SIMS (Secondary Ion Mass Spectrometry) analyses.

Constraints and risks

Work involving ionizing radiation: Internal training on radiation protection will be provided.

Compensation and benefits

Compensation

2300 € gross monthly

Annual leave and RTT

44 jours

Remote Working practice and compensation

Pratique et indemnisation du TT

Transport

Prise en charge à 75% du coût et forfait mobilité durable jusqu’à 300€

About the offer

About the CNRS

The CNRS is a major player in fundamental research on a global scale. The CNRS is the only French organization active in all scientific fields. Its unique position as a multi-specialist allows it to bring together different disciplines to address the most important challenges of the contemporary world, in connection with the actors of change.

CNRS

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