43 PhD student (M/F) - Corium thermodynamics

Job Description

Thesis Subject

In case of a severe accident in a pressurized water reactor (PWR), the various materials (fuel, cladding, and vessel) will react with each other to form a metal-oxide mixture called corium. The existence of a miscibility gap in the high-temperature liquid mixture will lead to its stratification into layers, whose thickness depends on the chemical composition of the mixture. A key question for safety calculations is the heat flux imposed by the corium on the vessel: this is necessary in order to determine the conditions for its potential failure and the initial conditions of the interaction between the corium and the concrete, the ultimate containment barrier. Retaining the corium within the reactor vessel through external cooling is now used in some Generation III reactors and also in SMR (Small Modular Reactor) designs. This system constitutes a corium containment strategy in the event of a severe accident. Therefore, understanding the thermodynamic properties of the corium is essential for predicting its thermal behavior.
The objective of this thesis is to improve the thermodynamic description of the corium system. This involves acquiring experimental data in the Fe-O-U-Zr system, chosen as a first approximation, to inform the thermodynamic modeling based on the CALPHAD (CALculation of PHAse Diagrams) method. The phase equilibria and thermodynamic properties of the intermediate phases will be studied at different temperatures. To this end, samples of selected compositions will be prepared at temperatures of interest. The crystalline structures and chemical compositions of the different phases at equilibrium will be determined by various characterization techniques (EPMA, XRD, SEM-EDS-EBSD). Thermodynamic properties such as the heat capacity and enthalpy of formation of defined compounds will be measured by differential thermal analysis and isothermal dissolution calorimetry, respectively. The miscibility gap in the liquid state will be studied using high-temperature heating methods (Joule furnace and laser heating) to determine the compositions of the liquid phases at equilibrium. The experimental results will then be taken into account to improve the models on the Fe-O-U-Zr system in the TAF-ID (Thermodynamic Advanced Fuels – International Database) database developed at the NEA/OECD [1].
[1] C. Guéneau et al, TAF-ID : An international thermodynamic database for nuclear fuels applications, Calphad, 72 (2021) 102212

Your Work Environment

This PhD will be conducted within the MPGM team at UMET (Materials and Transformations Unit, University of Lille) in collaboration with the CEA (Paris-Saclay University, Corrosion and Materials Behavior Research Department) and CIRIMAT (University of Toulouse).

The primary work location will be at UMET in Villeneuve d'Ascq, with regular visits to the CEA in Saclay.

Constraints and risks

The handling of radioactive material will be carried out in compliance with current regulations and under the control of the radiation protection advisor.

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.

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