A high-fidelity multiphysics system for neutronic, thermalhydraulic and fuel-performance analysis of light water reactors

The behavior of the core in a Light Water Reactor (LWR) is dominated by neutronic, thermalhydraulic and thermomechanic phenomena, as well as a complex set of feedback mechanisms between these physical domains. Thus, one of the current trends in computational reactor physics is the implementation of multiphysics applications that can capture these interactions to provide a consistent description of the core. Another key line of work is the development of high-fidelity numerical tools that increase the modelling resolution and eliminate strong approximations used in nodal-level solvers. Multiphysics and high-fidelity methods rely on the availability of High Performance Computing (HPC) systems, which determine the feasibility and scope of this type of simulations. The aim of this thesis is the development of a multiphysics system capable of performing coupled neutronic, thermalhydraulic and fuel-performance analysis of LWR cores using a high-fidelity methodology. To achieve this, the continuous energy Monte Carlo particle transport method is used to simulate the neutronic behavior without relying on major physical approximations. To handle full-core pin-by-pin burnup calculations, a data decomposition scheme with a domain decomposition particle tracking method is proposed and implemented. Combining Monte Carlo neutronics with subchannel-level thermalhydraulics and full fuel-performance analysis of all fuel rods, an extremely detailed representation of the core is achieved, pushing the computational requirements to the limits of HPC systems. From the software perspective, an innovative object-oriented coupling approach is used to increase the modularity, flexibility and maintainability of the tool. The accuracy of this three-code system is evaluated using experimental data from two operating power plants, a Pre-Konvoi PWR and the Temelín II VVER-1000 reactor. For these two cases, the results of full-core burnup calculations are validated using critical boron concentration and pin-level neutron flux measurements. These simulations serve to illustrate the cutting-edge modelling capabilities of the developed tool and to assess the feasibility of this methodology for industrial applications.