A computational fluid dynamics code with URANS turbulence model was used to simulate the flow in a complex geometry of the rod bundle of the Korean experimental device MATiS-H. We have found k-omega-SST turbulence model as a very good choice for this type of flows, where explicitely resolved large turbulent structures are clearly separated from the small structures, which are described by the turbulence model.
COBISS.SI-ID: 30262055
Large Eddy Simulations were used to investigate the dynamics and complexity of the instantaneous flow field and to thoroughly explain the local flow mechanisms associated with the heat transfer enhancement at the heated plate. Development of coherent flow structures is analyzed - their quasiperiodic propagation and disintegration on the heated plate result in a heterogeneous but on average rather stable heat removal from the heated plate. It was shown that the heat transfer at multiple impinging jets is mainly governed by two mechanisms, a convective cooling by the tangential flow in a close proximity of the jet impingement point, and by intense quasi-periodic quenching caused by large-scale vortical structures.
COBISS.SI-ID: 30239783
The applicability of the heat transfer models for typical fuel-water and fuel-sodium interaction conditions are analysed and discussed. The important differences of sodium properties compared with water require not just adequate modelling of the film boiling regime but also adequate modelling of the transition boiling regime. In subcooled conditions there are a stable and an unstable mode of the film boiling regime. Models were proposed for the stable and unstable mode of the film boiling regime and for the transition from the film boiling regime towards the transition boiling regime.
COBISS.SI-ID: 30011687
The evolution of grain misorientations (also called orientation gradients) at and close to the free surface of polycrystalline aggregates under tensile straining is analysed within the crystal plasticity finite element model. Mean and median grain misorientations are calculated on a free surface of the model and compared to electron backscatter diffraction (EBSD) measurements on 316 and 304 stainless steel taken from the literature. A linear correlation between the mean/median grain misorientation and the imposed macroscopic plastic strain is found to be in excellent agreement with the measurements.
COBISS.SI-ID: 29093415
Equipment for mitigation of an extended blackout is investigated. The analysis is done with deterministic safety analysis methods. A strategy to prevent core heatup and not overfill steam generators is proposed. Six types of reactor coolant system loss scenarios are investigated. The pump flowrates and the available start time to feed steam generators are determined.
COBISS.SI-ID: 29074471