METHODS FOR VERIFICATION AND PRELIMINARY VALIDATION TEST OF THE GEOMETRY NAVIGATION ENGINE IN THE MONTE CARLO TRANSPORT CODE TRIPOLI-5®.

Monte Carlo simulation is a widely used methodology in particle physics, nuclear medicine, reactor engineering, and many other scientific and engineering fields. One of the crucial aspects of these simulations is the transport of particles through complex geometries, which requires a highly accurate and efficient geometry navigation engine. The geometry navigation engine is responsible for determining the path of particles through materials and structures with complex geometries. This process includes managing particle interactions with various materials, determining collision points, and updating particle trajectories based on their interactions. The accuracy of this component is essential to ensure that the simulation results are reliable. TRIPOLI-5® represents a cutting-edge advancement in the realm of massively parallel and natively HPC-oriented stochastic particle transport codes, a collaborative development effort between CEA and IRSN initiated in 2022. Central to the efficacy of a Monte Carlo transport code is the accurate representation of the system geometry under investigation. This involves decomposing the domain into volumes, each characterized by a specific material composition. The geometry navigation engine plays a crucial role, providing critical information such as the composition in which a particle resides, the distance to the nearest geometrical boundary, and the subsequent volume the particle will traverse. Initially, TRIPOLI-5® relied exclusively on a geometry navigator utilizing the ROOT package, a robust tool developed by CERN. However, recognizing the need for enhanced performance and flexibility, a novel native geometry engine, AGORA, has been integrated into TRIPOLI-5®. AGORA adeptly handles nested geometries through the use of ”universes”, with each universe comprising elementary cells defined using Constructive Solid Geometry (CSG). A CSG cell is depicted using a combination of half-spaces defined by elementary surfaces (such as planes, spheres, cylinders, cones, or quadrics) and Boolean operators (intersection, union, or complement). The overarching geometry adopts a tree-like structure, where each cell may contain a material (acting as a leaf of the tree), a universe, or a lattice, which itself contains a list of universes. The objective of this thesis is to develop mothods to rigorously verify the reliability of the AGORA native geometry engine and to conduct preliminary validation test to ensure its integration with the TRIPOLI-5® Monte Carlo transport code.