The paper illustrates the results of the computer assessment of the form alteration in WWER-1000 core baffle obtained via the solution to the coupled thermoelastoplastic task considering the strains of irradiation growth and creep. In the modeling of the contact conditions, the temperature redistribution is considered due to the incompliance of the coolant flow in the contact zone between the core baffle and in-vessel core barrel with the design conditions. The modern approaches to the modeling of strains of the irradiation growth and irradiation creep in austenite steels are used in the space-limited environment under neutron exposure and elevated temperature. The finite element analysis involves the mixed scheme of the finite element method, which allows determination of the stress-strain state with high accuracy. The calculations are performed in the two-dimensional statement for the cross-section of the core baffle with the maximum damaging dose and irradiation temperature under the condition of the generalized plane strain. The results of the calculations are presented for full-scale reactor operation and scheduled shutdown to recharge the fuel cluster at the end of core life. The data on the distribution and value of the gap between the core baffle and barrel, as well as the spacer grids of the edge fuel assemblies and reactor core baffle edges, have been obtained from the median values of the dose dependence on swelling at different temperatures in Kh18N10T austenite steel.

The procedure of fracture resistance calculation for WWER primary equipment components has been improved. In particular, this refers to the reactor pressure vessel (RPV) and steam generators (SG) under normal operating conditions and emergencies. The developed calculation procedures and software make it possible to determine the significant effect of such factors as deformation stress history, residual technological heredity, analysis of temperature dependence of stress intensity factors for the postulated crack, regularity and density of the finite element mesh in the crack front on the assessment of WWER-1000 RPV fracture resistance. The paper proposes the methodology for justifying the place and orientation of the postulated crack to obtain the most conservative assessment of fracture resistance in the area of RPV inlet nozzles. It is shown that elastoplastic calculations in the thermal shock simulation can help to improve estimates of RPV strength and lifetime.  It was established that not taking into account the elastoplastic deformation history, residual technological stresses after heat treatment and corrosion effects can result in non-conservative assessment of fracture resistance of coolant header welding to SG PGV-1000M shell under normal operating conditions and emergencies. The calculation methodology and software for assessing stress-strain state of in-vessel internals were improved taking into account state-of-the-art approaches to modeling of radiation-induced swelling deformations and dependence of metal mechanical peculiarities on exposure doses and temperature.

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