A postdoctoral fellowship is proposed on the a posteriori estimates for the mixed finite element discretization of the multigroup diffusion criticality problem.
The objective is to develop efficient and reliable a posteriori estimates for a multigroup diffusion criticality problem with strong spatial heterogeneities, i.e. a model where the parameters, typically the coefficients of the equations, vary rapidly in space. Mathemically speaking, the criticality problem is a non-symmetric generalized eigenvalue problem.
At the reactor core scale, using simplified models is common in the nuclear industry. Precisely, the simplified models can be the neutron diffusion model or the simplified transport model. We derived rigorous em a posteriori error estimates for mixed finite
element discretizations of the neutron diffusion source problem, and proposed an adaptive mesh refinement strategy that preserves the Cartesian structure. A first application of this approach to the criticality problem was performed. Regarding the industrial context and specifically the numerical simulations, our approach is part of the development of a mixed finite element solver called MINOS in the APOLLO3 code. Further extensions of the a posteriori estimates were studied such the multigroup diffusion source problem and a Domain Decomposition decomposition denoted the DD+L2 jumps method. The enlisted approaches are based on the formulation of a source problem. The objective is to extend the a posteriori approach to a non-symmetric generalized eigenvalue problem.

A precise description of the transport of electrons and photons in matter is crucial in several of the CEA's flagship fields, notably radiation protection and nuclear
instrumentation. Their validation requires dedicated parametric studies and measurements.Given the scarcity of public experimental data, comparisons between calculation codes are also used. The challenge for the coming years is to qualify these codes in a broad energy domain, as certain discrepancies between their results have been identified during preliminary SERMA studies involving the coupled transport of neutrons, photons and electrons. The VALERIAN project involves seizing the opportunity created by a unique data collection Campaign planned for 2025-2026 at the IRFU (DRF) to better characterise these discrepancies. The IRFU has undertaken to check at least 750 pixel modules for the new trajectograph of the ATLAS experiment, as part of the rejuvenation of the large detectors at CERN. Numerous measurements with beta sources will be carried out in 2025-2026 for the qualification of these modules.

The sodium group of DM2S (department of CEA Saclay) develops numerical coupling tools in order to realize accidental case studies (fast transient). The physical domains concerned are neutronics, thermo-hydraulics and mechanics. The subject of this post-doc deals within this framework.
The aim is to carry out several studies: the integration of a coupling within the CORPUS platform, to carry out studies in order to test (and introduce) in the coupling the impact of the deformation of the assemblies by the Temperature on the flow of liquid sodium, the use of the neutronic cross sections generated by the code APOLLO3, the study of other accidental cases, and extend the modeling to the subchannel and pin scales.