2023, Maltsev, D. A. , Frolov, A. S. , Stepanov, N. V. , Safonov, D. V. , Кулешова, Евгения Анатольевна, Kuleshova, E. A., Fedotov, I. V.

Nickel is an essential alloying element in steels used as structural materials in the most common nuclear power reactors of the VVER type. The paper considers reviews the results of structural studies of traditional and advanced materials of the vessels and internals of VVER-type reactors with high nickel contents in their compositions. It is shown that an increased nickel content (up to 5 wt.%) in the steels of VVER pressure vessels contributes to the formation of a more dispersed structure with a smaller size of substructural elements and an increased density of dislocations, as well as a higher volume density of carbide phases. The revealed features of the structure of the reactor pressure vessel steel with high nickel content have the prerequisites for improving the strength and viscoplastic properties due to the increased number of barriers both for the dislocation motion and brittle crack propagation. Using the example of materials for VVER internals, it is shown that the nickel content increased in them up to 25 wt.% contributes to an increase in the volume density of radiation defects (dislocation loops of various types) and radiation-induced phase precipitates (G-phase). As nickel increases from 10 to 25 wt.%, there is a tendency to reduce swelling, which contributes to less shape change of the components of the reactor vessel internals. At the same time, in the steel with the highest nickel content, the highest nickel content was found in the near-boundary regions of the matrix, which contributes to greater austenite stability and a lower probability of the formation of an embrittling α-phase. The data obtained in the work on the effect of nickel alloying on the steel structural phase state and service characteristics were used in the development of new materials for the vessels and internals of advanced reactors.

2019, Frolov, A. S., Gurovich, B. A., Maltsev, D. A., Safonov, D. V., Kuleshova, E. A., Кулешова, Евгения Анатольевна

© 2019, Pleiades Publishing, Ltd.Abstract: The paper presents microstructural studies of specimens cut from fuel elements made of E110 spongy zirconium-based alloy after operation in a VVER-1000 before reaching the burnup of ~35 MWd/kg U. As a result of exposure to high temperatures and neutron irradiation, significant changes in the phase composition of fuel cladding materials appear: change in the size, density, and composition of β-Nb particles; change in the composition of the Laves phase; formation of dislocation loops of α type, as well as δ and γ hydrides. The main structural elements determining the degradation of the mechanical properties of the E110 alloy under irradiation are dislocation loops and fine-phase precipitates owing to their relatively large density. The data obtained can be used to construct dose dependences of microstructural changes with the aim of predicting the residual life of claddings and fuel assemblies as a whole.

2019, Gurovich, B. A., Frolov, A. S., Maltsev, D. A., Safonov, D. V., Kuleshova, E. A., Кулешова, Евгения Анатольевна

© 2019 Elsevier Inc.Microstructural studies of fuel cladding (made of E110 alloy based on sponge zirconium) after operation in VVER-1000 conditions (up to ~13 dpa) were carried out. The essential microstructural elements, which are responsible for the degradation of this material under the influence of operational factors, are established. It is known that in the process of irradiation, beta‑niobium needle-shaped precipitates are formed (in addition to the dislocation structures), which, upon reaching a specific fluence of fast neutrons, form periodic structures (with a bulk density of ~2–3∙1022 m−3). However, for the first time in this work, it was shown that relatively low doses of irradiation (~1.5 dpa) are characterized by the formation of needle-like phases with the high bulk density of ~4∙1022 m−3, which decreases with increasing of irradiation dose. This indicates the coagulation process of these particles during further operation of the fuel rods as a part of the VVER-1000 Fuel Assembly (FA). It is also shown in this work that the threshold dose for the formation of -type dislocation loops in alloy E110 (under the specified irradiation conditions) does not exceed 5.6 dpa.