Development of general principles of fatigue strength assessment steel structures of nuclear power plants units considering special operation conditions

The fatigue strength of the steel structures of nuclear power plants determines the possible period of their safe operation in terms of fatigue damage accumulation. These structures are locatedin special operation conditions, including elevated temperatures of environmental conditions, episodic temperature loads with a significant temperature gradient, etc. Reliable assessment of the fatigue strength of steel structures is of particular relevance because most units at Ukrainian nuclear power plants have already exhausted their design life and are at the stage of long-term operation. At the same time, in terms of fatigue strength assessment, state building codes are focused on traditional steel structures subjected to standard loads and impacts and do not take into account these special operating conditions. Nuclear and radiation safety regulations do not contain technical requirements for calculating the fatigue strength of steel structures and establish only general regulatory requirements. The article develops and formulates general principles of fatigue strength assessment of steel structures of nuclear power plants, taking into account the special operation conditions, as well as the degree of their responsibility for ensuring nuclear and radiation safety.