The nuclear industry’s transition toward higher fuel enrichments, aimed at improving fuel cycle economics and reducing waste volumes, requires rigorous criticality safety assessments to justify the use of existing storage infrastructure. A widely used licensing approach, the Reactivity Equivalence Method, assumes that fuel assemblies with higher enrichment and burnable absorbers are safe for storage if their infinite multiplication factor k_inf in a simplified core geometry matches that of a licensed reference fuel. This thesis evaluates the validity of this method for a VVER-1000 fuel assembly containing gadolinium rods within Fresh Fuel Storage Container and Spent Fuel Pool (SFP) configurations, utilizing continuous-energy Monte Carlo (MCNP 6.2) simulations.