RF State Research Centre JSC SPA “CNIITMASH” (Moscow, Russia):

N. P. Anosov, Cand. Eng., Senior Researcher, e-mail: NPAnosov@cniitmash.com
V. N. Skorobogatykh, Cand. Eng., Director of Material Science Institute, e-mail: VNSkorobogatykh@cniitmash.com
L. Yu. Gordyuk, Senior Researcher, e-mail: LUGorduk@cniitmash.com
Zh. V. Yurgina, Engineer, e-mail: ZVUrgina@cniitmash.com

The study considered the possibility of refusing to use the shift of the critical temperature of brittleness (ΔT_C) in the assessment of irradiation embrittlement of VVER RPV (Reactor Pressure Vessel) materials. The methods of calculation brittle strength using critical brittle temperature or brittle-ductile temperature were examined as the alternative. The brittle-to-ductile transition temperature TP is determined immediately at the inflection point of the normal standard probability distribution, whereas the level of impact energy KCV corresponding to a given σ_0.2 value intersects line of the normal standard probability distribution at the point T_C that is located much lower and to the left from T_P on the temperature diagram of impact toughness. When avoiding usage of ΔT_C, the nonadditive summing ΔT_C and T_C0 is eliminated. Instead, actual radiation embrittlement coefficients T_C0 = –60 °C, AF = 23, n = 1/3 are taken for calculation from the most conservative melt in terms of ΔTc among certification specimens lots of the base material, steel 15H2NMFAA. as the in for the base metal. In this case, the lifetime equal to 54 years is guaranteed. It was obtained that the refusal to use ΔT_C in the assessment of irradiation embrittlement of VVER RPV steels allows us to statistically substantiate the actual resources:
– 210 years for 15H2NMFAA steel and 307 years for 15H2NMFA grade 1 steel based on Т_C (avoiding using ΔT_C) with T_C0 = minus 77 °C;
– 117 years for 15H2NMFAA steel and 127 years for 15H2NMFA grade 1 steel based on Т_P (statistically substantiated) with T_C0 = minus 57 °C.
The work was financially supported by the Ministry of education and Science of Russian Federation in the framework of Agreement about granting of subsidy №14.579.21.0116 (unique agreement identificator RFMEFI 57915X0116).

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