In recent years, small modular reactors have drawn a lot of interest from all over the world. Innovative techniques are combined in small modular reactor designs to provide passive safety features, proliferation resistance, speed of construction, simplicity, and modularity, as well as reduced costs.  Water, gas, and liquid-metal-cooled reactors are among the several small modular reactor concepts that are now under development worldwide. Despite some design changes, the bulk of these designs follow a common set of design principles to improve plant safety and robustness, such as removing plant design vulnerabilities whenever possible, lowering accident probabilities, and limiting accident impacts. This paper describes ways of assessing reliability indicators of mechanical equipment of small modular reactors and nuclear power plants, as well as possible ways to increase their reliability. The first circuit of RITM-200 was selected. An extensive scientific literature published in the form of Scientific and Technical Document (STD) is used to predict the failure rate, which can subsequently be utilized to calculate device and system reliability with variable accuracy. During the execution of the work, the failure rates of each equipment in the circuit were obtained and then used to calculate the circuit’s reliability.