Hitri z natrijem hlajeni reaktorji so pomembna smer razvoja jedrske tehnike. V primeru težke nesreče s taljenjem sredice lahko nastanejo energijske interakcije med hladilom in raztaljeno sredico (parne eksplozije), ki lahko ogrozijo celovitost reaktorske posode. Poznavanje in napovedovanje fizikalnih procesov med interakcijo taline s hladilom je pomembno z vidika varnosti. V prvem delu naloge smo predstavili pomen in vlogo SFR v energetiki ter opisali glavne tehnološke značilnosti. Podali smo osnovne pristope k jedrski varnosti ter obravnavali potek in blaženje hipotetične težke nesreče s taljenjem sredice. Pri tem smo se osredotočili na interakcijo med reaktorskim hladilom in staljeno sredico. V drugem delu magistrskega dela smo obravnavali filmsko uparjanje okoli delca taline v podhlajenem toku hladila. Z uporabo računalniške dinamike tekočin smo izdelali numerični model filmskega uparjanja. Pri tem smo uporabili enotekočinsko formulacijo dvofaznega sistema z zasledovanjem medfazne površine. Glavni prispevek magistrskega dela je razvoj in utemeljitev izvirnega modela uparjanja in kondenzacije v ekstremnih pogojih. Prav tako smo v sklopu študije podrobno preučili delovanje obstoječega Leejevega modela uparjanja in kondenzacije za simulacije filmskega uparjanja v toku podhlajene tekočine. Oba modela smo preverili tudi z analitično rešitvijo Stefanovega problema in primerjali z eksperimentalnimi podatki. Sodium-cooled fast reactors (SFRs) have emerged as a significant advancement in nuclear engineering, carrying crucial implications for the power industry. In the event of a severe core meltdown accident, the reactor vessel's integrity can be compromised due to energetic interactions between the coolant and the molten core, leading to vapour explosions. Understanding and predicting the physical processes during melt-coolant interaction are paramount for ensuring safety. The first part of the thesis presents the importance and role of SFRs in the power industry, outlining their key technological characteristics. It discusses fundamental approaches to nuclear safety and explores the course of a hypothetical severe core melt accident, along with potential mitigation strategies, with a specific focus on the interaction between the reactor coolant and the molten core. The second part focuses on film boiling around a melt particle in a subcooled coolant flow. A numerical model is developed using computational fluid dynamics, employing a single-fluid formulation of a two-phase system with interface surface tracking. The main contribution of the master thesis is the development and justification of an original phase change model ELMEC (Enhanced Lee Model for Extreme Conditions). Additionally, the study thoroughly investigates the performance of the Lee evaporation and condensation model for film boiling simulations in a subcooled flow. Both models are validated using analytical solution of the Stefan problem and experimental data.
