Search

The paper presents the results of the application of the refined calculation guidelines to the analysis of the stress-strain state and fracture resistance of the equipment elements of the NPP primary circuit system with WWER reactor, in particular, the cylindrical part and the zone of the reactor pressure vessel inlet nozzle, coolant collector welded joint in a steam generator, baffle, and reactor internals' shaft under the operating and emergency modes of thermomechanical loading. The calculation methodology is based on the use of the modern models and methods of solution to the nonlinear boundary tasks of non-isothermal thermal viscoplasticity and tasks of fracture mechanics using the refined mixed schemes of the finite element method with increased accuracy. They allow one to obtain reliable solutions to the tasks considering the deformation history of thermomechanical loading, modern concepts of fracture mechanics and approaches to the modeling of brittle-viscous fracture defects, irradiation swelling and creep of metal, as well as as the structural elements, under the conditions of elevated temperature, intensive neutron irradiation and nonstationary modes of thermomechanical loading. The authors obtained and analyzed the calculation results for the cylindrical part and zone of the inlet nozzle of the WWER-1000 reactor pressure vessel, coolant collector welded joint in a steam generator, baffle, and reactor internals' shaft using the proposed guidelines. The results imply the possibilities of the proposed recommendations and make it possible to analyze some general tendencies and features of the application of the refined calculation models to justify the strength and life extension of the NPP structural elements under investigation. [ABSTRACT FROM AUTHOR]

We present the results of numerical evaluation of the possibility of application of additional thermomechanical treatment to the welded joints of the headers with connecting pipes of PGV-1000 steam generators from WWER-1000 reactor units of nuclear power plants with an aim to decrease the level of stresses formed after maintenance and in the process of subsequent operation. It is shown that this type of treatment is quite promising for extending the service life of the unit. [ABSTRACT FROM AUTHOR]

Additional heating of a thickened portion of the steam generator connector during postrepair thermal treatment of the header-connector weldment leads to a decrease in residual tensile stress levels. It is shown that during hydrostatic tests performed after thermal treatment inelastic strains on the inner connector surface are reduced, which inhances the cycle life of the weldment. [ABSTRACT FROM AUTHOR]

The procedure for calculating the life of header - steam generator connector weld joints is proposed. It allows for running out the material plasticity reserve upon static cyclic elastoplastic loading as well as operating conditions, local stress concentrations, and residual stresses after welding. [ABSTRACT FROM AUTHOR]

General methodological approaches to solving the problems of strength and life of NPP equipment and results recently obtained in this field at the Pisarenko Institute of Problems of Strength of the National Academy of Sciences of Ukraine are outlined. The urgency of the strength and life issues for reactor pressure vessels and steam generator shells is demonstrated. Application of a comprehensive calculation and experimental approach to the stress-strain state analysis is illustrated by the example of steam generator joints with defects. [ABSTRACT FROM AUTHOR]

The paper describes a method and main results of a refined stress-strain state evaluation for a welded joint of the hot collector to steam generator nozzle of a nuclear power plant with a WWÉR-1000 reactor, which takes into account a fuller range of the actual loading conditions in operation. In calculations, we considered the stresses induced by uncompensated thermal expansion of the reactor elements. The results of 3D finite element calculations suggest that the level of local stresses in the area of the joint exceeds the metal yield stress. The calculated stresses for the outer nozzle surface agree satisfactorily with the in-situ strain measurement data. [ABSTRACT FROM AUTHOR]