Safety systems of AP1000 nuclear reactor This paper aims to determine the safety of one of the technologically most advanced pressurized water reactors, nuclear reactor AP1000. In the first part by analyzing Risk study results (WASH1400, German Risk Study) the goal is to determine the security level of nuclear power plants to the impact on human health and the environment. at nuclear power plants in the past. The goal is to point out main disadvantages and problems because of which the public perceives nuclear power plants as not safe enough. The second part explains basic properties, operation mode and safety of pressurized water reactor. Special attention will be given to defense-in-depth philosophy and active safety systems and their shortcomings which led to the development of passive safety systems. The objective of studying nuclear reactor AP1000, which has been produced and developed by Westinghouse Electric Company, is to analyze passive safety systems and its components. The comparison of the AP1000 reactor with previous models of pressurized water reactors shows economic viability of AP1000 reactor. Furthermore, technological progress of AP1000 indicates lower dependence of safety systems on electrical power sources.