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Results of numerical analysis of stress intensity factors K I for semielliptical surface cracks in the WWER-1000 reactor pressure vessel by emergency cooling simulation with known engineering procedures, the equivalent spatial integration and direct methods are presented. Engineering procedures employ the results of numerical solution of axially symmetric boundary value problems of thermoelasticity based on the mixed mesh-projection scheme of the finite element method implemented in the RELAX software. The three-dimensional K I computations were performed with the SPACE software.Keywords: finite element method, mixed mesh-projection scheme, stress intensity factor, equivalent spatial integration method, direct method, semielliptical crack, reactor pressure vessel.One of the conditions of reliable service of nuclear power plant equipment is the reactor pressure vessel (RPV) integrity both in normal operation and in an emergency. Under RPV operation conditions caused by an emergency, in particular by thermal shock, the basic strength criterion for the RPV material is assumed to be its ability to resist brittle fracture. Stress intensity factor calculations are an appropriate basis for this.The present study cites the results of comparing calculated K I values for a longitudinal semielliptical surface crack in the WWER-1000 RPV obtained by engineering and numerical procedures. Among the first ones are the procedures employing approximate formulas [1, 2] and dimensionless K I values calculated by the method of weight functions [3,4], among the second ones are the procedures making use of the equivalent spatial integration method [5] and the direct method [6] based on solving the boundary value problem of thermoelasticity with the mixed mesh-projection scheme of the finite element method (FEM) [7], which provides a higher accuracy of determining thermostress and strain fields as compared to the classical finite element displacement method.The stress intensity factor by engineering procedures [1-4] is determined from the relationwhere σ is the calculated stress and Y is the dimensionless function for different points of the crack front allowing for crack dimensions and the RPV wall thickness. The stressed state on the crack surface ( Fig. 1) is expressed in terms of stresses (Eq. 1), which are proposed to calculate along the crack with different approximating functions from stress-strain state calculation results for the integral structure. 1380039-2316/07/3902-0138

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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.Introduction. The relief of undesirable residual stresses induced by welding during repair jobs of the header-PGV-1000 steam generator connector weldment of a WWER-1000 reactor is provided by thermal treatment, including heating, holding at elevated temperature for residual welding stress relaxation, and further cooling. The phenomenon of residual stresses arising during thermal treatment of the header-steam generator connector weldment is not completely understood, which determines a current interest in investigation of this problem.Earlier data [1] on the optimization of thermal treatment of the header-steam generator connector weldment after repairment were used to propose its conditions that ensure a decrease in maximum residual stresses. These calculations account for the bending moment effect on the weldment on the side of the main circulation pipe (MCP), but do not take into consideration the rigidity of MCP-reactor pressure vessel (RPV) connection and stress redistribution under further service loadings.The present communication reviews refined calculation results for stress-strain state kinetics in the headersteam generator connector weldment, with simulation of thermal treatment and further service loading, including hydrostatic tests and normal operations.Choice of a Calculation Scheme. Kinematic ties of elements (steam generator, MCP hot branch, and RPV) of "small"-and "large"-series reactors are similar and differ only in their layout. The calculation model of a small-series steam generator is shown in Fig. 1. The loading scheme accounts for the rest of the steam generator and RPV on rollers and a support collar, respectively, as well as the rigid fixing of the MCP end in the RPV wall. The weldment design, its most loaded element being the thinned portion of the steam generator connector, including the weld joint, is depicted in Fig. 2. This connector portion takes up loads, affecting the steam generator on the MCP side, the weight of structural elements, connected with the header, and of a coolant, as well as pressure-induced loads in the primary and secondary steam generator circuits.The calculations were performed with SPACE software [2], providing the solution of the three-dimensional problem of thermoplasticity with the account of loading history.Physicomechanical properties of the steam generator metal were assumed to be dependent on temperature. Inelastic deformation of the material during relaxation by the end of holding was measured by the equation of isotropic strain hardening with the account of the temperature effect [3]

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