Reactor Physic and Thermal Hydraulic analyses for the OECD/NEA MPCMIV Benchmark

High-fiidelity, multi-physics Modeling and Simulation (M&S) tools are being developed and utilized for a variety of applications in nuclear science and technology, and show great promise in their abilities to reproduce observed phenomena for many applications. These M&S tools enable rigorous modeling of coupled behaviors that needs to be properly validated against experiments. The Multi physics Pellet Cladding Mechanical Interaction Validation (MPCMIV) benchmark is organised in this context by the Nuclear and INdustrial Engineering (NINE) company in co-ordination with Studsvik, under the guidance of the NEA Expert Group on Multi physics Experimental Data, Benchmarks and Validation (EGMPEBV). It is an international project that involves the partecipation of universities and organisations from all over the world. The first revision of the input and output specifications of the benchmark was published in April 2018, but a lot of the boundary and initial conditions necessary to adress the different exercises in which it is organised are still missing. The work done in this thesis gives an important contribution to the completion of the specifications and demonstrates the validation of the experimental data through high-fidelity M&S tools. The analysis involves two out of the three physical domains of interest of the benchmark: Reactor Physics and Thermal Hydraulics. The Reactor Physics analysis focuses on the R2 Swedish Research Reactor, and it has the aim to derive the missing initial isotopic compositions of the fuel assemblies by performing first different infinite lattice depletion calculations for all the assembly types and then the full core burn-up calculation of a core cycle. All the models and simulations are carryed out with the Monte Carlo code Serpent 2. For the Thermal Hydraulics area, the RELAP5 code is used to build the model of the in-pile loop test facility inserted inside the R2 core, which is used to perform power ramp tests. The selected cold ramp test is then analysed by validating the model with experimental data through the demonstration of the achievement of the steady state conditions, and then the all test is simulated in a transient analysis. All the results of the simulations are compared with the experimental data to demonstrate validation approaches for both traditional and novel M&S tools. The multi-physics effort required to carry out the MPCMIV benchmark make it a challenging and complex project, and a great opportunity to study different tools and modeling approaches for research porpouses.