Nikolskyi M. Improvement of methods for modeling the fuel element cladding damage in VVER nuclear power plants to increase the operation efficiency.

The thesis proposes a new solution of the scientific and applied problem of improvement of the modeling method for calculation of the fuel element cladding damage based on taking into account the thermal cycling and emerging xenon oscillations, in order to increase the nuclear power unit operation efficiency and, at the same time, considering the security requirements. An analysis of the control object, methods and models used when calculating the fuel element cladding damage, has been done. A dynamic model of the VVER nuclear power unit based on the lumped modeling of steam generators, turbines and circulation loops, as well as using a multi-layer reactor model, considering the thermal cycling and emerging xenon oscillations, in order to evaluate the axial offset and the cladding damage parameter, has been developed. The VVER-1000 nuclear power unit properties based on the proposed efficiency criterion for cyclic operation and transient modes with different static control programs, considering their inherent internal disturbances and their influence on the axial offset and the fuel cladding damage parameter, have been studied. A method for calculating the fuel cladding failure probability at VVER-1000 normal operation, taking into account for fuel elements in any fuel assembly (FA) the energy release FA distribution nonuniformity, as well as the factors determining the cladding damage parameter, has been worked out.