More accurate modeling of the radiation embrittlement of a calibration metal on the basis of the shift criteria and envelopes of the dose-time dependences experimentally confirms that the modeling error corresponds to the variance band limits of the results of tests performed in control samples and reflects the structural nonuniformity of the metal of large-size blanks. It is recommended that high-quality VVER-1000 vessel steel with critical brittleness temperature from -44 to -78°C and from -78 to -121°C be used to eliminate the risk of brittle fracture of the core shells of GEN-IV VVER vessels.To eliminate the risk of brittle fracture of the core shells of GEN-IV VVER vessels, it is necessary to develop vessel steel that decreases the critical brittleness temperature admissible during operation to zero. This requires reducing to a minimum the conservatism employed when determining the guaranteed values, the error in modeling the dose-time dependence of T cr , and the effect of the chemical and structural nonuniformity on the change of the critical brittleness temperature when fabricating and using large-size shells.Error in Dose-Time Dependence Modeling and the Conservative Approach to Evaluating T cr . During the manufacture and use of VVER vessels, depending on the time, temperature of heating and cooling, deformation, irradiation, and other technological and operational factors reversible and irreversible brittleness processes, which are modeled by the time, dose, and dose-time dependence of T cr , occur in the vessel steel [1][2][3]. The main characteristic of resistance to brittle fracture is the critical temperature described by the very simple mathematical model:where T crA is the maximum admissible critical brittleness temperature at the critical point; T cr is the critical brittleness temperature which depends on the operating time of the vessel and is determined by the envelope of the fitted curve reflecting the dose-time dependence; T cr0 is a conservative estimate of the critical brittleness temperature in the initial state, independent of the operating time of the vessel; ΔT[F(t)] = A F [F(t)/F 0 ] 1/3 is a conservative estimate of the shift of the critical brittleness temperature, which depends on the operating time of the vessel and is determined by the envelope fitting the
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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.