Analysis of the safety classification of structures, systems and components in nuclear power plants

Classification of the equipment in nuclear power plants according to their safety has been needed since the years when the reactors were first designed and put into operation. Existing methods for the safety classification of structures, systems and components have been developed in the light of experience gained from the design and operation of existing power plants. Today, safety classification schemes created with the experience gained from certain power plant designs are used to identify structures, systems and components that are important for safety. However, different approaches are applied when creating these classification schemes. For this reason, there are uncertainties for some structures, systems and components when classifying, and their safety class differs. In this thesis, using the ATHLET code, double-sided cold leg break in a VVER-1000 type nuclear reactor was modeled and the safety classes of selected safety systems were tested and verified. In addition, as a result of the modeling, the classification of the safety system whose safety class is uncertain was clarified.