It is proposed that the fatigue strength of structures in nuclear power plants with a quite long service life be analyzed in two stages: first, the type and location of the process and the effect of basic factors are determined by method of direct analysis of stable cycles and then a more accurate stepped analysis of the deformation kinetics is performed. The real properties of a material are systematized, taking account of creep, in ways that depend on the different types of processes. The methods for calculating the conditions and mechanisms of the progressing shape change and alternating-sign flow are refined. An example of the instability of the processes of cyclic deformation, which limits the possibility of operating structures beyond the limits of elastic adaptability, is examined. The possibilities and conditions for algorithmitization of the choice of material models and ensuring computational accuracy in calculations of deformation kinetics are discussed.