One of the main principles in designing a nuclear power plant is generating safety and preventive tactics to achieve protection of individuals, society, the environment and the power plant systems against disasters and severe hazards resulted from nuclear radiation. Different engineering disciplines contribute in improvement of safety standards for power plants which leads to various design requirements to ensure that the safety of the plant is provided. Architectural design contributes in enhancing safety as well. The kinds of design principle requirements an architect must be concerned with during designing in order to increase the safety of the plant is the most challenging questions for architectural designers. The goal of this research is to achieve tactics and effective principles in order to prevent accidents and dangers and decrease the side effects to improve the safety of the plant. One of the main methods on studying architectural design of the power plant is the analysis of the current advanced power plants. In other words, the research questions could be traced in design ideas, being expressed in preliminary phase of power plant design.    In order to analyze the architectural design of the power plant, it is essential to describe the concept of the safety and main resultant goals and the main threatening occurrences which the power plant would confront. Based on this proposal, firstly the idea of the defense in depth would be studied and the related tactics in order to protect the power plants would be analyzed in the following. In this paper the EPR, an evolutionary pressurized water reactor in Europe which has been designed and constructed, is surveyed as a case study. Since the buildings and structures shaping the power plant are quite a lot, the study analyses the architectural design of the most important and sensitive buildings of this power plant in order to find all reasonably practicable architecture measures which prevent accidents in power plants to mitigate their consequences. The survey shows the architect-designer must always consider protection of power plant buildings against external and internal dangers and different aspects of danger and prevent the expansion of dangers. Regarding the research conducted, the architect-designer must consider the combination of reasonable measures and the following techniques in order to improve the safety of the plant: 1. Physical arrangement and proper positioning of spaces and building to improve the safety. 2. Designing multiple structures in order to protect the sensitive systems and equipments. 3. Designing annulus between buildings in order to prevent expansion of dangerous accident. 4. Physical separation of equipments, spaces and buildings in order to mitigate the consequences of danger. 5. Designing efficient building regarding functionality and resistance against danger. Considering all those solutions, architectural designs could offer immense help in preventing accidents in power plants and mitigating their consequences as well as improving the safety of the buildings.