[en] There are two VVER-440 type reactors in Loviisa Nuclear Power Plant. The first unit has been in operation since 1977 and the second since 1980. The availability of the plant as well as the operational experiences of the I and C systems are good. However it is obvious that the lifetime of the original I and C systems is not sufficient to guarantee the good availability of the plant in the future. Due to this fact a project for the renewal of the existing I and C systems has been started at Loviisa Nuclear Power Plant. In the project the analogue I and C systems will be renewed by digital I and C systems in four phases during 2005...2014. Simulators will be utilized extensively in the project to assure that the renewal of I and C systems can be realized safely and economically. An engineering simulator will be used in the design and validation of the modifications of the renewal I and C systems. A development simulator is aimed for the design, testing and acceptance of the new Man Machine Interface. A testing simulator will be used for the testing of the new I and C systems and retuning of the controllers mainly during the Factory Acceptance Tests. A training simulator will be used in training the operators and the other technical personnel in the operation of the new monitor-based control room facilities. All the simulators in the renewal project are based on APROS (Advanced PROcess Simulator) Simulation Software. Fortum Nuclear Services Ltd and the Technical Research Centre of Finland have developed APROS Simulation Software since 1986. APROS is a good example of the real multifunctional simulation software; i.e. it can be used in process and automation design, safety analysis and training simulator applications. APROS has been used extensively for various analysis and simulation tasks of the Loviisa Nuclear Power Plant in the past years. It has also been applied to various nuclear and thermal power plants elsewhere. First a short overview of Loviisa Nuclear Power Plant, Loviisa Training Simulator, APROS Simulation Software and the Loviisa I and C renewal project are given in the paper. Then a concept of the engineering, development, testing and training simulators is presented. Finally the utilization of the simulators in Loviisa I and C renewal project is described and benefits and risks gained on the use of the simulators in this kind of project are discussed. (author)