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The high conservativeness of the evaluation of the service life of VVER-1000 vessels is due to the operational reliability margin and the high error in determining the initial computational data. A structural analysis of the error in critical brittleness temperature investigations is presented and the factors which have a large effect on the error in constructing the dose-time dependences of the critical brittleness temperature are determined. In constructing dose-time curves, the use of the critical temperature of a calibration metal and heat-treatment regimes of calibration samples makes available and permits checking a wide range of structures that is characteristic for large blanks, makes it possible to take account of radiation embrittlement effects and radiation-stimulated reversible brittleness, decrease the error in determining the guaranteed values to T cr ± 5°C, and eliminate the large effect of structural nonuniformity on objective predictions made for a reactor vessel.Reliable prediction of the service life of VVER-1000 vessels with computational validation of the strength and reliability of the materials used for the structural elements of the reactor facility is a topical problem of reactor materials engineering [1]. Computational reliability is determined by the objectiveness of the mathematical model of the method and initial data, whose conservativeness is affected by the model error for the processes occurring in the vessel steel over a prolonged period of operation. Thus, in calculations of the brittle fracture resistance of the equipment in a nuclear power facility (vessel steel 12Kh2NMFA-A) according to PNAE G-7-002-86 the critical coefficient of stress intensity K 1C depends on the reduced temperature T red = T -T cr , due to the neutron irradiation of the material, including reversible brittleness, cyclic damage, and other factors.The effect of the error in determining the reduced temperature on the critical stress intensity coefficient can be illustrated on the following examples: the stress intensity coefficients are 74.7-118.4 and 54.5-212.9 MPa·m 1/2 for errors 60 ± 10°C and 60 ± 30°C, respectively (Fig. 1). Thus, the critical stress intensity coefficient increases considerably with increasing reduced temperature and its error of determination.

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