The Prandtl number 0.01 corresponds to the properties of liquid metals used for cooling in new generation fast nuclear reactors. A Direct Numerical Simulation database was obtained, which may be used for validation of less accurate models suitable for simulations in realistic geometries.
COBISS.SI-ID: 26107431
A detailed insight into complex flow dynamics and associated heat transfer phenomena of turbulent impinging jets was obtained using Large Eddy Simulation (LES). Results provided valuable information about unsteady jet dynamics and allowed us to interpret the governing heat transfer mechanisms. A complete spatial and temporal representation of the flow near the impingement plate was obtained with LES, so simulations represent a complement to experimental results. Besides its scientific contribution, the numerical studies represent an important upgrade of existing numerical databases on jet impingement flows, which is indispensable for development and validations of statistical turbulence models, often used for optimization studies in industry.
COBISS.SI-ID: 30239783
The flow in the rod bundle of the Korean experimental device MATiS-H was simulated using Unsteady Reynolds Averaged Navier Stokes (URANS) model for turbulent flow. It was shown that the URANS approach is suitable for the description of flows, where fluctuations at large length scales, explicitly described by the model, are separated from fluctuations at the smallest scales, which are considered by the model implicitly.
COBISS.SI-ID: 30262055
In upward air-water churn flow in a vertical tube, the liquid fed at the inlet is entrained upwards by the gas flow in the core, resulting in a wavy film flow. In experiments, liquid enters the tube normally to the flow direction through a porous wall. It was shown, that the simulated wave frequency is proportional to the normal liquid velocity at the inlet. This shows, that the wave frequency in churn flow does not depend solely on the tube geometry and liquid and gas flowrates, but also on the conditions at the tube inlet, which was not mentioned so far in the literature.
COBISS.SI-ID: 30823463
Heat transfer modelling approaches applicable for fuel-coolant interaction codes were discussed. First, the applicability of the adjusted Epstein-Hauser correlation for film boiling modelling was analysed. Second, for the stable mode of the film boiling regime, a modified correlation was proposed to enable better matching with experimental data at significant subcooling. For the unstable mode, an alternative correlation was proposed and assessed.
COBISS.SI-ID: 30011687
An experiment on hydrogen combustion which was performed at the Karlsruhe Institute of Technology (Germany), following a proposal by the research group, was simulated with a computational fluid dynamics code. Different models of turbulent combustion were implemented through user-defined functions and tested, with emphasis on the comparison between the simulated flame propagation and the experiment. Simulations have shown, that the used approach is suitable for considering hydrogen combustion in large enclosures.
COBISS.SI-ID: 31940135
As normal stresses at grain boundaries are assumed to be the key parameter for intergranular cracking, finite element simulations were performed, in collaboration with CEA (France), to calculate statistical distributions of intergranular normal stresses in irradiated stainless steel. Probability density functions were calculated in a realistic polycrystalline aggregate model as a function of macroscopic tensile strain and irradiation level. Results of simulations show that intergranular normal stress distributions widen significantly with increasing irradiation dose and show moderate to negligible dependence on the increasing macroscopic strain. Distributions are shown to be well represented by a bimodal master curve once the intergranular stress is rescaled by the macroscopic stress.
COBISS.SI-ID: 29487911
An improved thermal fatigue assessment of pipes subjected to turbulent fluid mixing was proposed using an improved spectral loading approach. The fluid temperature histories were generated synthetically preserving consistency with the first two statistical moments and power spectral densities of the measured/computed temperatures. This enabled a variety of physically sensible fluid temperature distributions. These were used in a novel analysis of the uncertainties involved in the calculated fatigue lifetimes. The ability to assess the uncertainties inherent in the calculations of fatigue lifetime was demonstrated.
COBISS.SI-ID: 28868903
Results from an uncertainty analysis of the probabilistic safety assessment of a reference nuclear power plant and their implication on risk-informed decision making were presented. The specific focus was on parameter and model uncertainties. The need for appropriate consideration of uncertainties in probabilistic safety assessment in order to adequately support risk-informed decision making was identified. The deficiency of usage of percentile measures was identified, as well as the needs for possible adaptation of risk informed decision-making principles to new nuclear power plants.
COBISS.SI-ID: 24957735
An analysis of the implications of electrical energy frequency increase on the safety of a nuclear power plant was presented. The change of the frequency was assessed for the subsynchronous resonance case study. The change of the plant parameters was analysed using a determinstic safety analysis code. The obtained results show that plant parameters, following the event of frequency change, remain within design bases.
COBISS.SI-ID: 32111911