B.A. Gurovich

Assessment of relative contributions from different mechanisms to radiation embrittlement of reactor pressure vessel steels

Abstract Experimental data on radiation embrittlement in pressure vessel steels of both Russian and American grades, obtained by the authors and also taken from the literature, have been analyzed to assess the relative contributions from the following mechanisms: radiation-induced hardening, inter- and intragranular segregation of impurities at precipitate/matrix interfaces. It is demonstrated that radiation-induced intragranular segregation of impurities frequently provides a significant contribution to radiation embrittlement of pressure vessel steels.

Intergranular and intragranular phosphorus segregation in Russian pressure vessel steels due to neutron irradiation

Russian reactor pressure vessel steels have been studied in three conditions: initial, irradiated and annealed. It has been established that irradiation induces both intergranular as well as intragranular phosphorus segregation. Fractographic studies demonstrated that brittle intergranular and ductile intergranular fracture surfaces of Charpy specimens appear as a result of intergranular and intragranular segregation, respectively. Transmission electron microscope (TEM) studies have revealed radiation-induced precipitates on interface boundaries to which intragranular phosphorus segregation occurs. Auger electron spectroscopy (AES) has been applied to detect phosphorus enrichment of fracture surfaces in the regions of brittle and ductile intergranular fractures.

Comparison of microstructural features of radiation embrittlement of VVER-440 and VVER-1000 reactor pressure vessel steels

Comparative microstructural studies of both surveillance specimens and reactor pressure vessel (RPV) materials of VVER-440 and VVER-1000 light water reactor systems have been carried out, following irradiation to different fast neutron fluences and of the heat treatment for extended periods at the operating temperatures. It is shown that there are several microstructural features in the radiation embrittlement of VVER-1000 steels compared to VVER-440 RPV steels that can cause changes in the contributions of different radiation embrittlement mechanisms for VVER-1000 steel.

Radiation damage of graphite and carbon-graphite materials

Abstract The results of the study of graphite and carbon-graphite materials obtained in the Russian Research Center “Kurchatov Institute” during a period of fifteen years are presented. The main structural effects and changes in pyrographites, nuclear (polycrystalline) graphites and carbon-graphite materials under irradiation are investigated. Irradiation temperatures and neutron fluences have been taken from wide ranges: ≈ 500–1200°C, and ≈ (0.01–2) × 10 26 n/m 2 respectively, ( E > 0.18 MeV). The following characteristics of materials are discussed: linear and volume changes in size, lattice parameters, radiation defect parameters, pore structure evolution, Youngs modulus change, etc. Particular attention is given to mechanisms, governing material radiation stability as a function of processing and irradiation conditions. The widely known effect of radiation dimensional change in irradiated graphite has been observed in the experiment. It has been demonstrated that the radiation defect parameters and magnitudes of radiation dimensional change are defined by initial sizes of graphite crystallites (for irradiation temperatures ≥ 500°C). It has been shown also that this effect determines the radiation stability in polycrystalline nuclear graphites. Distinctions in behavior of carbon-graphite materials under irradiation are shown.

The principal structural changes proceeding in Russian pressure vessel steels as a result of neutron irradiation, recovery annealing and re-irradiation

Abstract A wide range of pressure vessel steels – in the initial state (i.e. unirradiated), after irradiation, recovery annealing and re-irradiation – have been studied using microstructural and fractographic methods. The analysis of the data has allowed quality explanations of the key features of radiation embrittlement (RE) in reactor pressure vessel steels (RPVS) and resulting from initial- and re-irradiation to be proposed, and also to justify the existing concepts concerning the mechanisms of RE.

Post-irradiation studies of beryllium reflector of fission reactor examination of gas release, swelling and structure of beryllium under annealing

Abstract Hot-pressed high-density (TShG-type) beryllium was irradiated at 100°C up to the fast neutron fluence of 1 × 1026 n/m2. Transmutation tritium and helium contents were 652 and 4400 appm, respectively. Post-irradiation studies of beryllium consist of optical and electron microscopy, density measurements before and after isochronal annealing at the temperature range of 300–1100°C and thermodesorption gas spectrometry. Investigation shows the following: (1) Slight swelling of beryllium after neutron irradiation. (2) Spatial non-uniformity in the distribution of the pores. (3) Complicated dependence of swelling on annealing temperature caused by formation of gas porosity. In the temperature range from 500 to 800°C, swelling of beryllium was probably caused by growth of bubbles because of tritium mobility. At the temperature above 900°C swelling of beryllium was probably caused by growth of bubbles because of helium mobility. (4) Full degassing of the irradiated beryllium took place below its melting temperature.

Comparative study of fracture in pressure vessel steels A533B and A508

Abstract Two RPV steels with American denomination ASTM A508 and ASME A533B have been investigated with regard to radiation hardening, shift in ductile-to-brittle transition temperature and recovery behavior after thermal annealing treatments. Main emphasis has been given to a through examination and classification of fracture zones of tested Charpy-V specimens in dependence of irradiation and test conditions. The results of this investigation have been compared with the data found in Russian reactor pressure vessel steels.

Use of radiation effects for a controlled change in the chemical composition and properties of materials by intentional addition or substitution of atoms of a certain kind

This study is a continuation of works [1–12] dealing with the field developed by the authors, namely, to widen the possibilities of radiation methods for a controlled change in the atomic composition and properties of thin-film materials. The effects under study serve as the basis for the following two methods: selective atom binding and selective atom substitution. Such changes in the atomic composition are induced by irradiation by mixed beams consisting of protons and other ions, the energy of which is sufficient for target atom displacements. The obtained experimental data demonstrate that the changes in the chemical composition of thin-film materials during irradiation by an ion beam of a complex composition take place according to mechanisms that differ radically from the well-known mechanisms controlling the corresponding chemical reactions in these materials. These radical changes are shown to be mainly caused by the accelerated ioninduced atomic displacements in an irradiated material during irradiation; that is, they have a purely radiation nature. The possibilities of the new methods for creating composite structures consisting of regions with a locally changed chemical composition and properties are demonstrated for a wide class of materials.

The Effect of Radiation-Induced Structural Changes under Accelerated Irradiation on the Behavior of Water-Cooled Reactor Pressure Vessel Steels

In this paper the influence of fast neutron flux on the structural features and properties of VVER-1000 reactor pressure vessel steels was studied. It is shown that for high Ni steels the flux effect is due to hardening and non-hardening mechanisms of radiation embrittlement.

Selective Removal of Atoms as a New Method for Manufacturing of Nanostructures for Various Applications

The paper demonstrates a possibility for effective modification of the thin-film material’ chemical composition, structure and physical properties as result of selective removal of atoms by the certain energy ion beam. One of the most promising results of this effect consists in developing the new technology for 3D micro-and nano-structures production for various applications.