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539.4:621.165 I. I. Melezhyk, and T. V. ProtasovaThe thermostressed state and crack growth resistance of rotors are analyzed for various operating conditions using the procedures developed for their calculation. The kinetics of transverse cracks under high-cycle loading is considered.The majority of power-generating units of Ukrainian nuclear power plants (NPP) that generate about 52% of electric power are operating for than 20 years. The specified life of two power units of the Rivnenska NPP (above 30 years) will be exhausted in 2010-2011, and that of one power unit of the Yuzhno-Ukrainska NPP in 2012. In this connection, their equipment, including turbine plants, requires a comprehensive approach to evaluate the technical state, to assess the lifetime and to extend it. In contrast to high-temperature steam turbines, the material creep in NPP moist steam turbines is absent. Therefore, for assessing the damage in rotor elements it is important to determine the influence of low-cycle fatigue on the serviceability of the structure. As evidenced by operational experience, erosion-corrosion processes are decisive for NPP turbines.The most highly stressed areas in turbine rotors under varying modes of operation were determined with the help of boundary conditions of heat exchange for restricted schedules of cold and hot starts of the turbo unit and scheduled unloading, the calculations of unsteady thermal fields and the thermal stress state of rotors using the finite element method [1]. In so doing, transient problems on heat conductance and thermal stress levels were solved using the same finite element mesh [2]. The investigations of stress-strain state of rotors during a hot start (HS) of the turbine unit included the steady mode of operation, a scheduled outage with no loss of vacuum, and cooling for 8 h. All rotors were double flow rotors with the symmetry plane located in the center, therefore, only their symmetrical halves were considered.In a high-pressure rotor (HPR) of the NPP turbine (model K-100-60/1500), the maximum stress intensity is attained during a hot start of the turbine unit after its shutdown for 8 h and is 195 MPa in gaining 400 MW of power. The isothermal lines and stress intensity distribution corresponding to this case are presented in Fig. 1. The maximum stress intensity is attained on the internal surface of the rotor beneath the 5th stage and in disc grooves (Fig. 1b).Circumferential stresses on the internal surface of the rotor do not exceed their intensity of 220 MPa, whereas compressive axial stresses in disc grooves (190 MPa) are maximum. During the cold start (CS) period and in gaining 100 MW of power, the stress intensity in the HPR amounts to 170 MPa on the internal surface and is maximal during the whole start-stop period.For a medium-pressure rotor (MPR), the maximum stresses take place during the cold start of the turbine unit and in gaining 250 MW of power. In this case, the maximum radial temperature drop of 140°C is observed in the region near the 1st stage. The isothermal lin...