Effect of chemical and structural nonuniformity of vver vessel steel on the critical brittleness temperature under irradiation

Abstract

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

Conservative estimations of irradiation embrittlement of reactor pressure vessel steels for WWER-1000 lifetime prediction

“…The critical brittleness temperature T c is therefore the basic material constant used in calculations (as specified by PNAE G-7-002-86), and the T c –DTR dose-time relationships determined directly from SSs testing without finding Δ T c (Dub, Skorobogatykh, Anosov, Zharov, Zubchenko, Piminov and Shamardin, 2011; Dub, Skorobogatykh, Anosov, Zharov, Zubchenko and Piminov, 2011; Dub et al , 2012, 2016) appear to be quite realistic and virtually coincide with the realistic (Δ T c −73)–DTR values.…”

“…The critical brittleness temperature T c is therefore the basic material constant used in calculations (as specified by PNAE G-7-002-86 Rules of strength calculation for equipment and pipelines of nuclear power plants: Russian Rules and Standards in Nuclear Power Engineering), whereas the dose-time relationships T c –DTR are determined immediately from SSs testing avoiding using the Δ T c (Surkov et al , 1979; Dub, Skorobogatykh, Anosov, Zharov, Zubchenko, Piminov and Shamardin, 2011; Dub, Skorobogatykh, Anosov, Zharov, Zubchenko and Piminov, 2011; Dub et al , 2012, 2016).…”

The study of the brittle fracture resistance in fusion areas between RPV steel 15H2NMFA grade 1 and austenitic padding

“…Increasing concentrations of fluorine and copper from the level of BC for base chemical composition equal to 0.0025% and 0.025%, respectively, to the level of CC above that permissible in pursuance with TU (GOST R ISO 148-1-2013) equal to 0.0100% and 0.090%, respectively, corresponding to the upper level for 15H2NMFA-A steel, is accompanied with significant reduction of metal resistance against brittle fracturing (see Fig. 3) (Dub et al 2012, Anosov et al 1982, 1985.…”

Brittle fracture resistance of reactor pressure vessel steels in the initial state

“…Для заготовок используется металл промышленной обечайки из стали 15Х2НМФА (15Х2НМФА класс 1 базового химического состава) плавки 132009, содержащей 1,16% Ni, 0,0025% P и 0,025% Cu с заданным изменением структуры, выплавленной на высококачественной чистой шихте [9,10].…”