The modelling of the radial and axial interfaces of the core with the reflectors is source of approximations either for industrial Light Water Reactors (PWR and VVER types) but also for advanced concepts such as the Small Modular Reactors (SMR) and fast spectrum reactors (FSR) with an impact on the neutron flux distribution over the whole core.
In order to support the development of high fidelity resolutions to be applied to different reactor types, advanced 2D (for radial) and 3D (for axial) neutron reflectors models will be investigated,in this PHD. The analysis will start at level of the assembly (called lattice level) via an identification of relevant Figure of Merit (FoM) to be compared against reference calculations. The preliminary analisys will be completed by Monte Carlo reference calculations. The solutions will be then implemented in core calculations based on FEM methods such as the ones available on APOLLO3 codes for industrial-like homogeneous SP1 2 energy groups up to advanced SP3 pin-by-pin multi-groups solutions. This work will be realized in the framework of the neutronic code APOLLO3®. During his/her work the doctorand will be accompained by the technical team, and so he/she will be asked to intervene exclusively into the academic and theoretical part of the development work to support innovative industrial calculations and reference solutions.
Among the possible theoretical improvements of the classical models the following are identified:
• A new equivalence theory adapted to the Mixed Dual (Raviart Thomas) finite element method will be introduced in APOLLO3® Minos solver.
• In the classical diffusion approach, an equivalent (Benoist) diffusion coefficient is used. Unfortunately, the classical theory does not allow to treat (for example) the case when anisotropy is included in the emission density, or also when higher order expansion of the angular flux is done (SPN approximation). We propose the candidate to improve the classical model to include the possibility of defining anisotropic emission density in the core level and preserving the Benoist principle by using a generalization of this theory.