Influence of preliminary thermomechanical load on the integrity of the vessel of Ukrainian nuclear reactors in case of accidents of "large" and "small" leak

In works of extending lifetime of WWER-type reactors, it is necessary to obtain the brittle fracture resistance (BF) of the reactor pressure vessel (RPV). Implementation calculations for brittle fracture resistance is regulated by the technical PNAE of Ukraine. The objective of these calculations is to prevent catastrophic brittle destruction of the reactor pressure vessel, pipelines and pressure vessels from the existence crack-like defects for all operating regimes, including emergency situations (ES). The paper considers the most dangerous postulated emergency situation in operation is "large" and "small" leak in the RPV NPP. Calculations with Warm Pre-Stressing effect (WPS) of the RPV for the most dangerous scenarios have been presented, and an assessment of the brittle strength of RPV NPP is taking into account with WPS. The results of studies with factor of brittle strength safety are also presented without taking into account the Warm Pre-Stressing, comparing with the existing method for accounting this type of load.

Dissimilar welding of aluminum alloys 2024 T3 and 7075 T6 by TIG process with double tungsten electrodes

The aim of this work is to study the metallurgical and mechanical properties of dissimilar assemblies of 2024 T3 and 7075 T6 structural hardening aluminum alloy by TIG twine electrode arc welding process. It will include a weld performed according to optimized welding parameters followed by a study of the macroscopic and microscopic evolution of the dissimilar assembly (2024–7075) using optical and scanning electron microscopy (SEM); In addition, the phase compositions were analyzed with an energy dispersive spectrometer (EDS). Tensile and microhardness tests were performed. The tensile fracture was observed by SEM. We have found that this process thins the weld bead and reduces the size of the heat affected zone (HAZ) of the welded joint. The microhardness is lower in the melted area and higher on the side of the area affected by the heat especially for 7075 alloy, resulting in brittle strength and a sudden drop in breaking strength.

THE INVESTIGATIONS OF A PECULIARITIES OF PYROCARBON GAS PHASE DENSIFICATION OF POWDERS OF THE CATALYTIC CARBON FORMATIONS (CCFs), OBTAINED ON NICKEL

Investigations on gas-phase densification of the catalytic carbon formations (CCFs), obtained on nickel, using the method of radially driven pyrolysis zone were carried out. Straight dependence of the brittle strength of the CCFs, bonded with pyrocarbon (CCFBPyC), from the CCFs morphology, was shown. It was determined, that the result of decreasing of an amount of fibrous, fine-grained CCFs component is the increasing of strength of the pyrocarbon matrix . For the first time, carbon/carbon composite materials (CCCM ) without cracks, which contain refined or not-refined from nickel, carbon nanomaterials (CNM), were obtained.

Features of brittle fracture of steels at low temperatures

В статье рассмотрены особенности хрупкого разрушения сталей в условиях низких температур. Разрушение стальных конструкций чаще всего начинается от концентраторов напряжения (производственные дефекты, сварные швы и т.д.) В результате понижения температуры влияние этих факторов резко усиливается. В этом случае требуется применение металла, способного к пластической деформации при низких температурах, поскольку хрупкое разрушение по своим последствиям значительно опаснее, чем пластичное. Пластическая деформация осуществляется за счет перемещения дислокаций, которые являются проявлением несовершенства кристаллический решетки. Под влиянием напряжений при отсутствии препятствий дислокации свободно перемещаются в решетке металла. Понижение температуры приводит к тому, что возрастающий предел текучести достигает значений хрупкой прочности. Существенное влияние на хладостойкость стали оказывают примеси. Влияние примесей связано в первую очередь с загрязнением границ зерен сплавов и уменьшением сил сцепления на плоскостях спайности. Кроме этого, границы зерен характеризуются значительными нарушениями кристаллического строения и являются участками скопления дефектов структуры и включений. The article deals with the features of brittle fracture of steels at low temperatures. The destruction of steel structures most often begins from stress concentrators (manufacturing defects, welds, etc.) As a result of a decrease in temperature, the influence of these factors increases dramatically. In this case, the use of a metal capable of plastic deformation at low temperatures is required, since brittle destruction is much more dangerous in its consequences than plastic. Plastic deformation is carried out due to the displacement of dislocations, which are a manifestation of the imperfection of the crystal lattice. Under the influence of stresses in the absence of obstacles, dislocations move freely in the metal lattice. A decrease in temperature leads to the fact that the increasing yield strength reaches the values of brittle strength. Impurities have a significant effect on the cold resistance of steel. The influence of impurities is primarily associated with contamination of the grain boundaries of alloys and a decrease in the adhesion forces on the cleavage planes. In addition, the grain boundaries are characterized by significant violations of the crystal structure and are areas of accumulation of structural defects and inclusions.

A discussion on how, when and where surface processes interplay with extensional tectonic deformation

<p>Fascinating feedback relationships between surface processes and tectonic deformation have long been highlighted for convergent settings. Mountains influence local climate, with precipitation increasing with mountain height and focusing at windward-facing slopes. The resulting erosion reduces the elevation and width of mountain belts, in turn leading to a focussing of tectonic deformation and exhumation at eroding regions. Thus, in convergent settings, erosion and tectonic deformation show positive feedback by enhancing each other. In comparison, the role of surface processes in extensional settings has received less attention, which does not mean that erosion or sedimentation might not equally affect tectonics deformation during extension. In this presentation, i will review theoretical expectations, discuss numerical experiments, and pose questions on how, when, and where surface processes interplay with tectonic deformation during extension.</p><p>How: The removal of material by erosion is expected to decrease vertical crustal stress and reduce brittle strength (which is the main process leading to focussing of deformation in shortening). Sedimentation conversely increases brittle strength. However, sediments of low thermal conductivity in extensional basins can trap heat, increasing crustal temperatures, and reducing viscous crustal strength. Will brittle strengthening or viscous weakening dominate during sedimentation? And during rifting, is erosion the controlling surface process, or sedimentation, or both?</p><p>When: Usually, subsidence needs to create accommodation space before sedimentation occurs and rocks should uplift before they can be eroded. This would imply that surface processes need time to start up and cannot play a decisive role in initial stages of deformation. This then begs the question: once an extensional system starts to deform in a certain style, can surface processes still change the style? For rift basins, we find from numerical experiments that sedimentation favours symmetric basins over asymmetric half-graben and single basins over distributed deformation. For rifted margins, i have found that sedimentation promotes hyperextension by forming wide areas of thinned continental crust, thus supressing early break-up. These experiments point out that surface processes seem to be able to exert a control on the style of rifting. But at which stage in rift evolution do surface processes start to play a role? And is there a crucial timing, after which erosion and sedimentation no longer influence the extensional style?</p><p>Where: Analogous to convergent tectonic settings, erosion of rift footwalls can enhance tectonic deformation and, on a large-scale, turn a ‘passive’ margin ‘active’ in a tectonic sense. Footwall uplift provides a sediment source region, linking erosion to offshore sedimentation. For rifted margins, where does deposition of sediments (whether they are brittle strengthening or viscous weakening) play the most influential role in the rifting process? Can strong near-footwall sedimentation suppress footwall uplift, thus providing a negative feedback in the system?</p>

Strength models of the terrestrial planets and implications for their lithospheric structure and evolution

Knowledge of lithospheric strength can help to understand the internal structure and evolution of the terrestrial planets, as surface topography and gravity fields are controlled mainly by deformational features within the lithosphere. Here, strength profiles of lithosphere were calculated for each planet using a recently updated flow law and taking into account the effect of water on lithospheric deformation. Strength is controlled predominantly by brittle deformation at shallow depths, whereas plastic deformation becomes dominant at greater depths through its sensitivity to temperature. Incorporation of Peierls creep, in which strain rate is exponentially dependent on stress, results in the weakening of plastic strength at higher stress levels, and the transition from brittle to ductile deformation shifts to shallower depths than those calculated using conventional power-law creep. Strength in both the brittle and ductile regimes is highly sensitive to the presence of water, with the overall strength of the lithosphere decreasing markedly under wet conditions. The markedly low frictional coefficient of clay minerals results in a further decrease in brittle strength and is attributed to expansion of the brittle field. As plastic strength is influenced by lithology, a large strength contrast can occur across the crust–mantle boundary if deformation is controlled by ductile deformation. Effective elastic thickness for the terrestrial planets calculated from the rheological models indicates its close dependence on spatiotemporal variations in temperature and the presence of water. Although application of the strength models to observed large-scale surface deformational features is subject to large extrapolation and uncertainties, I emphasize the different sensitivity of these features to temperature and water, meaning that quantifying these features (e.g., by data from orbiting satellites or rovers) should help to constrain the internal structure and evolution of the terrestrial planets.

In-Vessel Core Melt Retention Strategy Applied for the Rivne VVER-440 Unit

In-Vessel Core Melt Retention (IVMR) strategy via external vessel cooling is widely applied for reactors of relatively low power like VVER-440. In this study, IVMR strategy was applied for Rivne-1, 2 units to prove the pressure vessel integrity. Based on initial data like heat flux for internal wall and external wall temperature, a series of calculations for different scenarios were performed. These calculations include non-elastic material properties: creep and plasticity. As the result, the wall ablation, radial displacements, stress and strains were obtained. To prove pressure vessel integrity four criterions have been checked. The first one is obvious — remaining wall thickness, to prove that that RPV won’t be melted right through. The second one is visco-plastic collapse — lack of monotonous increase in deformations, in case of FEM solution result convergence can be interpreted as resist against such failure. The third — sustainable external cooling, thus the gap between RPV (due to radial elongation) and thermal protection shield must be 10 mm at least. The last one is brittle strength, this calculation was performed on a separate model.

The characteristics of the winter durum wheat varieties according to grain quality and pasta properties

The current paper has presented the study results of grain quality and pasta properties of the new and promising winter durum wheat varieties developed in the FSBSI “Agricultural Research Center “Donskoy” in 2016–2018. The purpose of the study was to evaluate winter durum wheat varieties according to such traits as grain quality and pasta properties to identify the best genotypes and recommend them for use in the breeding process and wider introduction into production. There have been identified the varieties “Yubilyarka” (96%), “Kristella” (94%), “Lakomka” (92%), “Diona” and “Yantarina” (91%) with maximum values of general hardness. All studied genotypes have formed the nature weight of grain corresponding to a first quality class (from 786–814 g/l). There have been identified the varieties “Kristella” (13.9%), “Donchanka” (13.8%), “Diona” (14.0%), “Yakhont” (14.0%), “Yubilyarka” (13.6%), “Yantarina” (13.7%), “Uslada” (13.6%), “Zoloto Dona” (13.6%), “Solntsedar” (13.9%) and “Almaz Dona” (13.5%) with protein percentage in grain corresponding to a first quality class. As a result of the study, it was found that all the studied varieties had good rheological properties of gluten and formed a DCI from 80 units (the variety “Eyrena”) to 102 units (the variety “Donchanka”) and belonged to the 2-nd group. The varieties “Diona”, “Eyrena”, “Yakhont”, “Yantarina” and “Solntsedar” had high rheological properties of dough. There have been identified the genotypes of the varieties “Donchanka” (613 μg/%), “Solntsedar” (626 μg/%) and “Almaz Dona” (630 μg/%) with the maximum concentration of carotenoid pigments, which could be used as sources to improve the trait “carotenoid content”. Throughout the years of study, the varieties were characterized by high indices of dry pasta color (4–5 points). According to a brittle strength of dry pasta there have been identified the varieties “Kristella” (775 g), “Donchanka” (774 g), “Diona” (757 g), “Yantarina” (782 g), “Solntsedar” (766 g) and “Dinas” (769 g) with the best indices of the trait. The varieties identified both by a single and by a set of traits characterizing grain quality of winter durum wheat and its final products, can be used in the breeding process as an adaptive initial material. The introduction of the best varieties into production will partly solve the problem of deficiency of high-quality durum wheat in the south of Russia.

Determination of stress condition and friction coefficient from orientation distribution of outcrop-scale faults

<p>  Friction coefficients along faults control the brittle strength of the earth's upper crust, although it is difficult to estimate them especially of ancient geological faults. This study proposes to estimate the friction coefficient of faults with stress condition which activated them by the following procedure. Stress tensor inversion using fault-slip data can calculate principal stress axes and a stress ratio, which allows us to draw a normalized Mohr’s circle. Assuming that faulting occurs when the ratio of shear stress to normal stress on the fault (the slip tendency) exceeds the friction coefficient, a linear boundary of distribution of points corresponding to the observed population of faults should be found on the Mohr diagram. The slope of the boundary (friction envelope) provides the friction coefficient. Since this method has a difficulty in the graphical recognition of the linear boundary, this study automated it by considering the fluctuations of fluid pressure and differential stress. The fluctuations yield a density distribution of points representing faults on the Mohr diagram according to the friction coefficient. Then we can find the optimal value of friction coefficient so as to explain the density distribution.</p><p>  The method was applied to some examples of natural outcrop-scale faults. The first example is from the Pleistocene Kazusa Group, central Japan, which filled a forearc basin of the Sagami Trough. Stress inversion analysis showed WNW-ENE trending tensional stress with a low stress ratio. The friction coefficient was calculated to be about 0.7, which is typical value for sandstone.</p><p>  Another example is from an underplated tectonic mélange in the Cretaceous to Paleogene Shimanto accretionary complex in southwest Japan along the Nankai Trough. The stress condition was determined to be an axial compression perpendicular to the foliation of shale matrix. The friction coefficient ranges from 0.1 to 0.3, which is extremely low indicating a weak plate boundary under the accretionary wedge.</p>