Nuclear power plants (NPPs) are equipped with several independent safety systems, which purpose is to prevent possible failure situations and accidents that may disturb normal operation of the NPP and cause damage to a reactor. One important NPP safety system application is an emergency diesel generating (EDG) system that operates as an on-site emergency power supply system for the NPP. Its main purpose is to generate and supply electricity to NPP’s necessary safety and control systems (safety auxiliaries) in case of regular power supply from an off-site electricity grid fails (loss-of-offsite power, LOOP) and during other critical emergency events. The EDG system consists of a large diesel engine, a generator, a common base frame, auxiliary systems, and control and instrumentation equipment that all ensure proper function of the entire system.The main goal of this study is to examine and discover what are the most important performance requirements specific for the nuclear EDG system. In order to achieve this aim, this thesis carries out a comprehensive review of the EDG system’s components and their functions based on Wärtsilä’s technology. In addition, it investigates topics such as the role of the EDG system operating with the NPP, applicable nuclear regulations, standards and frameworks, applicable qualification procedures and possible factors influencing the EDG system’s performance. Instead of numerical and calculation based approach, the performance of the EDG system is studied mainly from functional side.This study indicates that the necessary safety functions of the EDG system form a foundation for the most important performance requirements such as fast start-up in response to emergency demand, accepting and accelerating heavy motor loads in rapid succession to constant rotational speed, maintain load within acceptable frequency and voltage limits, etc. even under abnormal operating conditions. In order to achieve demanded capability for the nuclear service, the EDG system must successfully pass rigorous qualification programs such as performance testing, analysis, and environmental qualification. From the manufacturer point of view, design, manufacturing and qualification of this particular application’s equipment are challenging, and require strong know-how, constant research and development as well as keeping up to date regarding nuclear regulations and applicable standards.
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