Добірка наукової літератури з теми "Core baffle"

The paper illustrates the results of the computer assessment of the form alteration in WWER-1000 core baffle obtained via the solution to the coupled thermoelastoplastic task considering the strains of irradiation growth and creep. In the modeling of the contact conditions, the temperature redistribution is considered due to the incompliance of the coolant flow in the contact zone between the core baffle and in-vessel core barrel with the design conditions. The modern approaches to the modeling of strains of the irradiation growth and irradiation creep in austenite steels are used in the space-limited environment under neutron exposure and elevated temperature. The finite element analysis involves the mixed scheme of the finite element method, which allows determination of the stress-strain state with high accuracy. The calculations are performed in the two-dimensional statement for the cross-section of the core baffle with the maximum damaging dose and irradiation temperature under the condition of the generalized plane strain. The results of the calculations are presented for full-scale reactor operation and scheduled shutdown to recharge the fuel cluster at the end of core life. The data on the distribution and value of the gap between the core baffle and barrel, as well as the spacer grids of the edge fuel assemblies and reactor core baffle edges, have been obtained from the median values of the dose dependence on swelling at different temperatures in Kh18N10T austenite steel.

The paper describes the methodology for the calculation of neutron fluence and energy release in WWER-1000 reactor cavity and baffle using the Monte Carlo MCNPX code. It formulates an approach to the simulation of a 3-D neutron source and conditions for the transport of neutrons and photons in the core. The research presents preliminary results of neutron fluence and energy release calculation in WWER-1000 reactor cavity and baffle.

Oil liquid sloshing is a common phenomenon in automobile fuel tank under variable working conditions. Installing baffles in automobile fuel tank is the most effective way to suppress adverse influence caused by oil liquid sloshing. Different types of three-dimensional finite element models filling oil liquid are created, meshed, and simulated. The reliability of simulation results is verified by test. The concept of time–area value is proposed in this work. In order to explore the influence of different baffle factors on oil liquid sloshing, six factors are studied. Six kinds of influencing factors are height, structure, shape, spacing, number, and placement of baffles. The sloshing pressure and time–area value are the core parameters for evaluating the influence degree. Some results could be obtained by comparing the parameters of oil liquid sloshing under the same condition. High baffles and baffles with small spacing have obvious attenuation influence on the pressure of oil liquid sloshing. Low baffles, double baffles, parallel baffles, and the combined action of inertia force and gravity are more beneficial to the reduction of time–area value. Time–area value is the largest and the smallest in fuel tank with intersection baffles and low baffles, respectively.

Ukraine currently does not have a company to perform full neutronic calculations of VVER-1000 core. In this regard, the paper proposes a method of parametric assignment of volumetric heating due to gamma-radiation and the irradiation dose rate in VVER-1000 core baffle. The method significantly simplifies assessment of the stationary temperature, irradiation swelling and stress-strain state of pressure vessel internals. The method is based on the approximation of the input fields by polynomial s of nth degree in the radial and circumferential coordinates. Methodical error in the calculation of the stationary temperature field is 3,2 %, 12,7 % — in the calculation of radiation swelling, 33,0 % — in the evaluation of radial deformations of the core baffle. This allows to use the method for the preliminary assessment of technical condition of the VVER-1000 reactor internals.

The program is presented for investigations of the metal of the most irradiated elements of the WWER-440 reactor of the Novovoronezh NPP Unit 3 decommissioned after 45 years of operation. The fragments (cylindrical samples) were cut out from various zones of the core baffle and segment of forming ring of core barrel.

The developed model of the WWER-1000 reactor using MCNP6.2 (Monte Carlo N-Particle Transport Code) includes the detailed core taking into account the design of the fuel assemblies, as well as the baffle, the lower plenum, the fuel support columns, the core barrel, a downcomer, and the reactor pressure vessel. It allows implementing multifunctional calculations such as recriticality with various fuel configurations, the critical concentration of boric acid, determination of the axial and radial peaking factor in the reactor core, etc. For obtaining the more precise result of the cumulation nitrogen-16 formation rate, the contribution from different water volumes was taken into account: in the core, above the fuel and the top nozzle, in the top nozzle of the fuel assembly, in the bottom nozzle, between the fuel and the bottom nozzle, in the axial channels of the baffle, in the reflector. In order to obtain the realistic boundary conditions, the change of the isotopic composition in the fuel assemblies during one fuel cycle was calculated using the ORIGEN-ARP of SCALE software. Therefore, the influence of the nuclear fuel depletion of fuel assemblies in the WWER-1000 reactor on the change of the basic neutron-physical characteristics was determined such as the distribution of the neutron flux density with the energies necessary to initiate the 16O(n,p)16N reaction, the average number of neutrons per fission, the neutron spectrum and average fission energy. As a result, the dependence of the nitrogen-16 formation rate in the primary coolant system on the nuclear fuel burnup is obtained.

In many hydroelectric projects there is a need to safely dissipate the energy associated with the elevation of the water surface. When the flow is not passing through the turbines, bypass valves are often used. A valve that is commonly used is the fixed-cone valve. Fixed-cone valves, also known as Howell-Bunger valves, are devices often used to safely reduce flow energy at dams with medium to high heads. The valve directs the outflow into a conical hollow jet, which requires a large area for energy dissipation. The flow is controlled by an adjustable sleeve, also known as the gate which surrounds the valve and requires minimal power for operation even for large valves. Depending on the installation, the conical jet may need to be controlled by installing a fixed stationary hood or other structure to contain and direct the conical jet. While the hood reduces the spray, the use of the hood causes the formation of a concentrated hollow jet having a high velocity. To eliminate the hollow jet and dissipate much of the associated energy, the hood can have interior baffles. If the hood is not precisely placed relative to the valve, a phenomenon, known as backsplash, will occur. Backsplash is when a significant amount of water exits the upstream end of the hood. Backsplash is a concern for operators because it can prevent access to the valve during operation and can flood valve vaults. Because the use of fixed-cone valves and baffled-hoods are becoming more popular, the need for guidelines to correctly position the hood relative to the valve will benefit both engineers and contractors. In some hydroelectric sites, submerging the fixed-cone valve is used to control the spray and dissipate energy. Submerging the valve can have can produce violent flow conditions which can cause damage to a structure or heavy erosion. The use of a submerged fixed-cone valve is rarely used, and a submerged valve used with a baffled-hood has never been constructed. The study performed shows that the use of a baffled hood with a fixed-cone valve in submerged conditions performs well. The results may lead the way for more submerged fixed-cone valves in the future.

Coalition problems in e-markets attract attention from the research communities and industry. This research focuses on e-trading models relating to online coalitions. A new Core Broking Model (CBM), for online group-trading is presented. This aims not only to bring lower prices for buyers but also to create higher profits for providers. The survey of current online shopping sites in this thesis shows that it is almost impossible to find a site designed specifically for group-trading, although there are plenty of joint-selling activities and also many online group-buying sites. The former increases competitive advantages and benefits providers. However it allows cartels to take control of price and to disadvantage customers. Recently, the latter have become very popular. The major problem of these models is that they lack the ability to deal with the stability issue in coalitions, which therefore fall apart easily. The core, a concept from economics, provides solutions to ensure a stable coalition (Gillies 1953), but its certain problems have hindered researchers from applying it to a real-world market. Building an online group-trading model is essential. Developing such a new model for e-markets can be a real challenge. Three factors, namely (a) incentive compatibility, (b) distributed computing, and (c) less computational complexity, all have to be considered at the same time. The new model is based on the core and adopts some other solution concepts to resolve group-trading problems in e-markets. It involves bundle selling of multiple goods from several providers, offering volume discounts to many different buyers in group-buying on e-marketplaces. The CBM successfully creates a win-win-win situation for customers, providers and brokers in e-markets. The comparison between the results of the new model and the core shows the CBM is superior to the core in terms of the three factors mentioned above. The results of the simulation presented in this thesis demonstrate that the CBM can attract customers and deal with online group-trading problems in a large coalition. An extensive evaluation of the techniques in the CBM has been made and shows that all of them produced the desired results in the CBM effectively and efficiently.

Дисертаційна робота присвячена розробці чисельних і аналітичних методів розрахунку коефіцієнта інтенсивності напружень, (КІН) для некласичних проблем механіки руйнування, зокрема, для тріщин складної форми та для тріщин в тонкостінних конструкціях з врахуванням геометричної нелінійності, (ГН). Представлена модифікація методу Вільямса, що враховує затухаючі на нескінченності члени. Досліджено межі та надані рекомендації щодо застосування даного методу. Розроблено аналітичний метод розрахунку КІН в трубах з довгими осьовими поверхневими тріщинами з врахуванням ГН в залежності від внутрішнього тиску. Наведено результати верифікації величин КІН з отриманими в роботі чисельними розв’язками МСЕ. Побудовані чисельні моделі для розрахунку КІН та розкриття берегів тріщин в ГН постановці для наскрізних тріщин в залежності від змінної величини осьової сили. Побудована апроксимаційна формула, що описує вплив ГН ефекту для узагальненої осьової сили та безрозмірної довжини тріщини. Показана значимість ефекту для реальних лабораторних експериментів. Розроблено універсальний напіваналітичний метод розв’язку інтегро-диференційного рівняння теорії пружності для плоских тріщин нормального відриву довільної форми. Для перевірки аналітичних результатів побудовані чисельні моделі МСЕ для тріщин різної форми, наприклад, для прямокутної, внутрішньої півелітичної тріщини, тощо, та проведено співставлення результатів. Проведені практичні розрахунки КІН в часі для елементів конструкцій АЕС для різних сценаріїв протікання аварійних ситуацій. Створено ряд імітаційних моделей з вбудованою тріщиною, для якої розрахунки КІН проводилися методами нелінійної механіки руйнування. Для тріщин, що проходять через наплавлений матеріал, де відбувається стрибки напружень, обґрунтовано застосування методу функцій впливу, для чого розроблено аналітико-чисельну процедуру, що використовує частково неперервні базові закони навантаження.
The dissertation is dedicated to the development of numerical and analytical methods for calculating the stress intensity factor (SIF) for nonclassical problems of fracture mechanics, in particular, for cracks of complex shape and for cracks in thin structures with taking into account geometric nonlinearity (GN) and their applications in various industries, in particular, for nuclear power plants, for calculation of the elements of the reactor unit. A modification of Williams's method is presented, which describes the stress state in the crack tip. For modification of the classical approach in the considered method the additional members were presented, which are infinite in the crack tip, but attenuate at infinity. The main idea of the method is to divide the whole area of the body into two separate parts – internal one, which embraces the tip of the crack, and the external one. In the inner area, only the classic Williams functions are used, and in the outer area both the classical members and additional ones are used. At the boundary between the selected subdomains, the conjugation conditions are to be fulfilled, the essence of which is to equalize here the stresses and displacements. The very high efficiency of this method is shown for bodies that have the shape of a circle, or are infinite, where almost exact values (up to 6-7 digits) are achieved when using no more than 12-16 members of the expansion. However, for a very elongated rectangular body the method gives much worse results, and the error can reach up to 2%. The practical significance of the proposed approach consists in the obtaining the simple and effective tool for testing the capabilities of commercial packages for calculating the parameters of fracture mechanics, which, as we know, do not always provide the correct results for case when load is applied on the crack surfaces. A thin-walled pipe with a long surface crack is considered. The pipe, surface of which may contain the initial deviation form ideal circle, is loaded by inner pressure. In first time the problem of determining the SIF was considered in a geometrically nonlinear formulation, when changes in the geometry of the body in the process of deformation are accounted for linear material behavior. Based on the Chen-Finnie method, which considers the crack as concentrated compliance, and on original solution for geometrically nonlinear behavior of curved initially distorted beam, the compact analytical formulas are obtained, which gives the value of SIF for each value of inner pressure. Comparison of the analytical results with those obtained by careful numerical FEM analysis, on the one hand, showed their good correspondence, and therefore the accuracy and efficiency of both the analytical and numerical procedures are confirmed. On the other hand, for the first time in the scientific literature, the value of SIF in a geometrically nonlinear formulation are obtained for surface cracks in slightly distorted cylindrical shell with surface long crack. It was shown that even for perfectly circular pipes having the cracks with depth up to half of the thickness of pipe walls, loaded by moderate level of inner pressure, the geometrical nonlinear values of SIF can be 10-15% less than those at linear approach application. This is very significant practical result. Another geometrically nonlinear problem is numerically investigated by known commercial FEM software for the through crack, which is loaded by a significant value of additional longitudinal force (the main factor of geometric nonlinearity considered) and small value of internal pressure (linear consideration). This statement distinguished this task from research conducted at NASA (USA), where the pressure and axial force were proportional as to pipe with closed ends. The geometric nonlinearity of the study is investigated through an incremental increase in loads and the corresponding recalculation of the SIF for the already taken into account changes in the deformed geometry (curvature). A number of tasks for determining the SIF for different pipe radii and dimensionless force values were calculated. Dimensionless parameters, which characterize the deviation of the values of SIF from the linear one, are numerically determined. Application of least square method allowed to suggest the simplified analytical formula for calculation of these deviations. These results are of great theoretical and practical importance. In particular, it is shown that for real pipes the neglecting by influence of axial force in usual approach may lead to 4-6% error of SIF determination. It is noted that additional account for large values of pressure, possible plastic deformations, may further reduce the actual values of SIF. Thus, the significance of the problems and the need for further research in this direction are shown. The necessity of analysis of flat cracks of non-canonical shape in three-dimensional bodies is noted. This is due to the fact that almost all existing solutions in the literature and reference results in normative documents are given for cracks that have shape of an ellipse or its part. However, real cracks detected by non-destructive testing are irregularly shaped cracks. Therefore, it is necessary to create the analytical methods that would allow to assess the impact of the crack shape, and to verify them with careful numerical procedures by FEM. For this purpose, flat internal cracks in infinite 3D body are considered. The formulation of problems for them is reduced to well-known integro-differential equation of the theory of elasticity. Note, that exact fundamental analytical solutions of which exist only for a circular crack and only for some simple laws of loading for an elliptic crack. A universal semi-analytical method for solving the integro-differential equation of the theory of elasticity for plane cracks of normal separation of arbitrary shape has been developed. It is proposed to consider the displacement of the crack edges as a product of a certain function of the crack shape, which satisfy to known asymptotic behavior of the displacement field near the crack front, and a certain polynomial series. As for the functions of the form, three variants of their choice were investigated - a) classical, which depends on the squares of ratio of radial coordinate of the considered point, and the corresponding coordinate of contour point; b) multiplicative, based on the product of equations describing the straight sections of the crack contour, and c) the original Oore-Burns function, which is an integral of the crack contour from the inverse square of the distance of the considered point to each point of the contour. The results showed that the greatest accuracy is achieved by application of hypersingular approach with Oore-Burns function of form. The verification of results was performed for elliptic crack, semielliptic inner crack, rectangular crack. The results were compared with numerical ones calculated by FEM. Practical calculations of SIF dependance with time for NPP reactor ant its elements for different scenarios of emergency situations are carried out. A number of simulation models with a built-in crack have been created, for which SIF calculations were performed by nonlinear FEM analysis. For cracks going through the cladding, where stress jumps occur, the method of influence functions is elaborated, and analytical-numerical procedure used piece-wise continuous basic laws of loading. Practical calculations were performed for the nozzle of reactor vessel, the cylindrical part of vessel, the core barrel and core baffle. These calculations were used to justify the extension of the service life of several units of Ukrainian NPPs.
Диссертационная работа посвящена разработке численных и аналитических методов расчета коэффициента интенсивности напряжений, (КИН) для неклассических проблем механики разрушения, в частности, для трещин сложной формы и для трещин в тонкостенных конструкциях с учетом геометрической нелинейности, (ГН). Представлена модификация метода Вильямса, что учитывает затухающие на бесконечности члены. Исследованы границы и даны рекомендации о применении данного метода. Разработан аналитический метод расчета КИН в трубах с длинными осевыми поверхностными трещинами с учетом ГН в зависимости от внутреннего давления. Результаты хорошо коррелируют с полученными в роботе численными решениями МКЭ. Построены численные модели для расчета КИН и раскрытия берегов трещин в ГН постановке для сквозных трещин в зависимости от переменной величины осевой силы. Построена апроксимационная формула, что описывает влияние ГН эффекта для обобщенной осевой силы и безразмерной длины трещины. Показана значимость эффекта для реальных лабораторных экспериментов. Разработан универсальный полуаналитический метод решения интегро-дифференциального уравнения теории упругости для плоских трещин нормального отрыва произвольной формы. Для проверки аналитических результатов построены численные модели МКЭ для трещин разной формы, например, для прямоугольной, внутренней полуэллиптической трещины, и др., и проведено сопоставление результатов. Проведены практические расчеты КИН во времени для элементов конструкций АЭС для разных сценариев прохождения аварийных ситуаций. Для этого создан ряд имитационных моделей со встроенной трещиной, для которой расчеты КИН проводили методами нелинейной механики разрушения. Для трещин, что проходят через наплавленный материал, где происходят скачки напряжений, обосновано применение метода функций влияния, для чего разработано аналитико-численную процедуру, что использует частично непрерывные базовые законы нагружения.

What ingredient in Coke can remove rust from chrome? What is the bitterest substance on earth? What is the worst smelling one? In this entertaining tour of chemistry, John Emsley answers these and many other questions as he illuminates the materials that make up our world. Dozens of lively articles explore such well-known molecules as water, oxygen, and glass; versatile plastics like polypropylene, polystyrene, and polyurethane; even "elements from hell" such as Sarin (a lethal nerve gas). With no formulas, equations, or molecular diagrams to baffle the non-expert, each piece blends history, science, and anecdote, with many intriguing facts added to the mix. "The world of chemistry has never been made as entertaining," writes Nobel Prize-winning chemist Roald Hoffmann. Indeed, this book will fascinate everyone curious about the chemicals in the foods we eat, the clothes we wear, and the air we breathe.

Eugenia, Baroness Mnster, wife of a German princeling who wishes to be rid of her, crosses the ocean with her brother Felix to seek out their American relatives. Their voyage is prompted, apparently, by natural affection; but the Baroness has also come to seek her fortune. The advent of these visitors is viewed by the Wentworths, in the suburbs of Boston, with wonder and some apprehension. The brilliant Eugenia fascinates her impressionable cousins and their more worldly neighbour, but she is baffled by these people, 'to whom fibbing was not pleasing'. Meanwhile Felix, painter of trifling sketches, eases them all in and out of various amorous complications, with 'no fear of not being, in the end, agreeable'.

It was my pleasure to participate in Oleg’s 65th birthday celebration and to reminisce about the early days of Biochemical NMR. Oleg was always there. I remember in the summer in the early 1960s sitting on lawn chairs at a Gordon Conference and discussing the need for a meeting on biochemical NMR. This was to convene those with common interests, and out of this grew the 1964 meeting in Boston, which was the first International Conference on Magnetic Resonance in Biological Systems. In organizing the 1964 meeting Oleg was stalwart, in charge of the local arrangements at the old mansion, home of the American Academy of Arts and Sciences. The venue was much appreciated by the more than 100 attendees, and the smooth arrangements and elegant, although somewhat dowdy locale, contributed to the sense, generated by the meeting, that the field had a coherent scientific core and a meaningful future. In the early days of the 1960s the field of magnetic resonance in biological systems, brought together biannually by the society, had a coherence that was nurtured by the society. In those days the NMR and ESR methods were much less developed than they soon became, so that any reasonably competent spectroscopist could understand all the methods employed. Additionally, because the earlier studies concentrated upon the better understood biological molecules or processes, the breadth of the applications did not baffle a slightly informed biochemist. The rapid advances in definite understanding were thrilling to practitioners in the field, and individual efforts were motivated by a sense that the field was going to grow. By that time NMR was firmly established as a quantitative method in chemistry, solid state physics, and other material sciences so that with the results in hand it was logical to extrapolate to a future in which magnetic resonance could be central to biological research. These high hopes, however, required considerable confidence in extrapolation, because the individual findings were sometimes slight when compared to the exciting cutting edges of biological research.

And all the earth was one language, one set of words. And it happened as they journeyed from the east that they found a valley in the land of Shinar and settled there. And they said to each other, ‘Come, let us bake bricks and burn them hard’. And the brick served them as stone, and bitumen served them as mortar. And they said, ‘Come, let us build us a city and a tower with its top in the heavens, that we may make us a name, lest we be scattered over all the earth’. And the LORD came down to see the city and the tower that the human creatures had built. And the LORD said, ‘As one people with one language for all, if this is what they have begun to do, nothing they plot will elude them. Come, let us go down and baffle their language there so that they will not understand each other’s language’. And the LORD scattered them from there over all the earth and they left off building the city. Therefore it is called Babel, for there the LORD made the language of all the earth babble. And from there the LORD scattered them over all the earth....

This chapter investigates British socialism’s symbolic birth: Robert Owen’s unveiling of his plan for an entirely new social order in the summer of 1817. Although Owen has been canonized as a stalwart of the political left, his proposals baffled and enraged partisans across the ideological spectrum. Commentators had great difficulty deciding whether his “Plan” was radical or reactionary—or even if it was “political” at all. Using the vitriolic debates that consumed the Plan as a focal point (and drawing on contemporary commentators as varied as William Hazlitt, Thomas Malthus, and George Cruikshank), this chapter undertakes a revisionary interpretation of Owenite socialism that uncovers its latent aesthetic core. Owen and his followers have long been associated with utilitarian indifference, if not downright vulgarian insensitivity, to the arts. However, Owen’s very ambition to govern citizens without recourse to the state or the Church rests upon an aesthetic substratum. This chapter demonstrates that the curriculum Owen designed to produce human beings who would not require “politics” to produce consensus relies upon extensive training in the musical arts to inculcate the principle of universal harmony. The final part of this chapter locates the origins of British anti-socialist rhetoric at the juncture of Malthusian political economy and anti-Jacobin polemic.

This chapter is about the minerals based on silicon and oxygen, the silicates, the ones that make siliceous rocks. And because this means most rocks, apart from limestone and the other calcareous materials, they are often referred to as the “rock- forming minerals.” Let’s be clear at the outset that with these siliceous rocks we’re talking about silicate compounds, which involve the element silicon and a subgroup of silica minerals, which we’ll come to at the end of the chapter. None of this has anything to do with silicone, the synthetic polymer of multifarious uses. The principles discussed here are the same as those developed in the previous chapter, but the silicates present special challenges. Indeed, for a long time they were very tricky things to understand at all. The early geologists had at their disposal new ways of chemically analyzing minerals, and they applied them with gusto. They made impressively rapid progress, but they were baffled by the silicates. Their analyses showed that these minerals were dominated by silicon and oxygen but beyond that, well, they seemed too numerous, wildly varied, and inconsistent. It turned out to be well into the twentieth century before there was a breakthrough in understanding these perplexing compounds. The breakthrough took place when it dawned that X- rays could be used to study the structure of crystals—any crystals: geological, metallurgical, biological, and so on. Today, over twenty Nobel prizes have been awarded for work in this field, most recently in 2012. It’s even relevant to wine itself, through elucidating the structure of enzymes, proteins, and the like. (Incidentally, the use of X-rays to analyze crystals is quite different from its use in producing the familiar X-ray pictures of the human body.) In July 1912, the Bragg family rented a house, Whin Brow, at Cloughton, high above England’s Yorkshire coast. The father of the family, William, was a Professor of Physics at Leeds, and his 22-year-old son, Lawrence, was a precocious physics student at Cambridge. With an impending war, they were eager to escape the grimness of city life for a while, but even so, William took some work with him.

The internal core baffle structure of a PWR consists in baffles and formers attached to the barrel. Each baffle being independent, the connection between the core baffle sheets, the formers and the core barrel is done thanks to a large number of bolts (about 1500). After inspection, some baffle bolts have been found cracked. This behaviour is attributed to Irradiation Assisted Stress Corrosion Cracking (IASCC). In order to compute accurately the temperature distribution affecting these bolts, EDF has set up a research program. Due to symmetry reasons, only a 45° sector has been accounted for. The three-dimensionnal neutron flux and the gamma induced internal heating are calculated with a Monte-Carlo particle transport code named Tripoli-4. The by-pass flow inside the cavities is computed with the CFD code Code_Saturne with a finite volume technique. Finally, the temperature distribution inside the structure (including all bolts which leads to a considerable solid mesh size — about 236 millions tetraedra) is computed by the thermal code Syrthes using a finite element approach, taking into account both the heating due to the gamma heating deposit and the cooling by the by-pass flow. Calculations show that the solid thermal field obtained exhibit strong temperature gradients and high temperature levels but in very limited zones located inside the material. As expected mainly very limited regions located inside the material and near the corner close to the reactor center are exposed to high temperature levels. On the other hand, calculations clearly confirm that external bolts thightening the core barrel and the formers see temperature much lower than those thightening the baffles.

This Paper presents an improved estimation of reactor core baffle temperature distribution, during operation, at the nominal power level to address swelling problems of the reactor internals. Swelling is the main limiting factor in the reactor core internals long term operation of VVER-1000 nuclear units. The material irradiation-induced swelling and creep models are very sensitive to temperature distribution in metal, thus a more detailed analysis of the core baffle metal thermohydraulic cooling characteristics is required. A framework for CFD analysis of VVER-1000 reactor baffle cooling is presented. Firstly, an analytical model was developed to obtain boundary conditions and simplify CFD analysis, i.e. the real geometry of the cooling channels was replaced by equivalent elements, the core was presented as porous body with the appropriate characteristics. Secondly, the CFD analysis was performed using 60–degree symmetry, which included: core, baffle and core barrel, it is limited by the height of the baffle. Core is simplified as a homogeneous body with considering of spatial volumetric energy release. Core baffle is presented as monolithic body with considering of gamma-ray heat generation. Model includes a simplified geometry of connecting studs, considering cooling flow of the coolant through the nuts grooves. Calculated convection coefficient and temperature are in good agreement with analytical model, and give a more convenient result comparing to RELAP5/mod3.2. Obtained results were used to estimate baffle swelling process. Due to the less conservative results in temperature distribution swelling and creep deformations significantly decreased.

Abstract Common heat transfer enhancement techniques are found in many of today’s processes. Devices such as inclined baffles, rib turbulators, jet impingement, etc are all used in order to augment the thermal transfer of a process. Inclined baffles have been studied along with the combination of jet impingement techniques. Inclined baffles enhance heat transfer by enhancing large-scale fluid bulk motion and through tripped boundary layer flow separation. Impinging jets, created by perforating the baffle, create additional heat transfer through flow impingement on the heated surface. Rib turbulators create heat transfer augmentation by disturbing the thermal boundary layer, unlike baffles; ribs enhance heat transfer in areas near the heat transfer surface leaving the core flow largely undisturbed. This investigation investigates experimental heat transfer of turbulent flow in a rectangular channel with inclined solid and perforated baffles combined with rib turbulators for isoflux heating at the top surface of the channel. Combining ribs with baffles yielded an increase in average Nusselt Number, albeit, with a pressure drop penalty. In situations where rate of heat transfer is critical to the performance of a device combining ribs with baffle is a viable solution.

Traditionally, the brittle strength evaluation of reactor pressure vessel was the central issue in lifetime assessment of Ukrainian nuclear power plants (NPPs). The problem of swelling of the reactor core baffle only recently got due attention from the side of operator. Here the most efforts were given on numerical modeling of austenitic steel 08Kh18N10T swelling and its effect on induced stresses in core baffle and distortion of its geometry. The calculation shows that essential changing of core baffle dimensions is expected after 35–40 years of operation. Eventually this can lead to the contact with the core barrel. Yet, these predictions contain the big number of uncertainties related to the input data used in analysis: fluence distribution; temperature variation due to heat release induced by neutron and gamma radiation; thermal-hydraulic boundary condition between the baffle and coolant; and, especially, the adopted law of swelling in dependence with above factors as well as mechanical stresses. So, the second task was to measure the real geometry of baffle after 27 years of operation, to determine its change and compare these results with the numerically calculated data with accounting for the design tolerances. Thus, the spatial measurement system (SMS) equipped with ultrasonic gages was designed. It contains the central vertical beam which can move in vertical direction and rotate. To the lower end of the beam four horizontal levels are attached, which are equipped with device resistant to the hot water and radiation. The gages are used to measure the shortest distances to the edges of baffle. Two types of results were obtained. The first one are the measurements in the different horizontal planes obtained by rotation the SMS around the vertical axis with angular steps equal to 1 degree. These results were difficult to handle with and required a special mathematical treatment due to the possible shift of the centre of measurement. The second set of measurements was performed by moving the SMS in vertical direction. These data demonstrate the change of distance with the height. The results clearly show that problem of swelling do exists, and, in general, the measured patterns of the distortions along the vertical and angular coordinates correspond to numerically obtained results. Further work on baffle integrity is however needed.

It has been established by other authors [1] that the accelerations of the water confined by the reactor core baffle plates has a significant effect on the responses of all the fuel assemblies during LOCA or seismic transients. This particular effect is a consequence of the water being essentially incompressible, and thus experiencing the same horizontal accelerations as the imposed baffle plate motions. These horizontal accelerations of the fluid induce lateral pressure gradients that cause horizontal buoyancy forces on any submerged structures. These forces are in the same direction as the baffle accelerations and, for certain frequencies at least, tend to reduce the relative displacements between the fuel and baffle plates. But there is another confinement effect — the imposed baffle plate velocities must also be transmitted to the water. If the fuel assembly grid strips are treated as simple hydro-foils, these horizontal velocity components change the fluid angle of attack on each strip, and thus may induce large horizontal lift forces on each grid in the same direction as the baffle plate velocity. There is a similar horizontal lift due to inclined flow over the rods when axial flow is present. These combined forces appear to always reduce the relative displacements between the fuel and baffle plates for any significant axial flow velocity. Modeling this effect is very simple. It was shown in previous papers [2,3] that the mechanism for the large fuel assembly damping due to axial flow may be the hydrodynamic forces on the grid strips, and that this is very well represented by discrete viscous dampers at each grid elevation. To include the imposed horizontal water velocity effects, on both the grids and rods, these dampers are simply attached to the baffle plate rather than “ground”. The large flow-induced damping really acts in a relative reference frame rather than an absolute or inertial reference frame, and thus it becomes a flow-induced coupling between the fuel and baffles. This has a significant effect on the fuel assembly motions and tends to reduce the relative displacements and impact forces between fuel assemblies and baffle walls.

A set of experiments were conducted on the circumferential overlap trisection helical baffle heat exchangers with inclined angles of 20°, 24°, 28° and 32° single-thread and inclined angle of 32° dual-thread one, and a segmental baffle heat exchanger as a contrast scheme. The cylinder case of the testing heat exchanger is a common shell, while the tube bundle core could be replaced. The shell side heat transfer coefficient ho is obtained by subtract tube-side convection thermal resistance and tube wall conduction resistance from the overall heat transfer coefficient K. The curves of shell side heat transfer coefficient ho, pressure drop Δpo, Nusselt number Nuo, and axial Euler number Euz,o are presented versus axial Reynolds number Rez,o. A comprehensive performance index Nuo/Euz,o is suggested to demonstrate the integral properties of both heat transfer and flow resistance of different schemes, and the curves of Nuo/Euz,o versus Rez,o of the different schemes are presented. The results show that the scheme with inclined angle 20° performs better than other schemes, and the scheme with inclined angle 24° ranks the second, however the segment scheme ranks the last. The curves of Nuo/Euz,o of both schemes with inclined angle 32° of single-thread and dual-thread are almost coincident, even though their heat transfer coefficient and pressure drop curves are quite different. The results indicate also that for the circumferential overlap trisection helical baffle schemes the optimal inclined angle is around 20° instead of around 40° as rated by many literatures for the quadrant helical baffle schemes.

The vibration-reduction and sound-absorption properties of a truss-core sandwich beam are analyzed. The core is composed by the assembly of unit cells across both the length and thickness of the proposed beam. The cells have chiral geometry which features cylinders, or nodes, joined by ligaments, or ribs. The resulting assembly is characterized by a number of interesting properties that can be exploited for the design of alternative honeycomb or cellular topologies to be used in sandwich construction. The vibro-acoustic analysis of the considered beam is performed through a finite element model developed using a commercially available Finite Element package. In the model, the sandwich beam is constrained to a rigid baffle and divides two fluid domains of infinite extent. The dynamic performance of the beam is evaluated through the estimation of the vibration amplitudes of the two constraining layers, while the performance of the beam as an acoustic panel with high insulation characteristics is analyzed through the estimation of the sound transmission loss between the two fluid domains. A sensitivity study to investigate the influence of core configuration and geometry on the beam’s performance is presented. The results indicate the design flexibility offered by the proposed design, which allows modifying and optimizing the structural acoustic performance of the beam through proper selection of the core configuration.

Irradiation Assisted Stress Corrosion Cracking (IASCC) is a matter of great concern as degradation of core internal components in light water nuclear reactor. To clarify the IASCC initiation conditions of baffle former bolt (BFB), constant load stress corrosion cracking (SCC) tests were carried out in simulated PWR primary water (290, 320, 340°C) using C-ring type specimens. Based on the SCC test results, IASCC initiation time becomes shorter with increasing fluence and increasing applied stress, IASCC initiation threshold stress becomes lower with increasing fluence. A test temperature effect was observed in SCC initiation time, but it was not clear the effect of test temperature for SCC initiation threshold stress. These results suggest that IASCC initiation threshold criteria can be described with stress in specimen and fluence. This paper describes the whole evaluation procedure to secure structural integrity of irradiated baffle structure in PWR primary environments, including the threshold stress diagram of IASCC initiation and the irradiation creep formula.

There have been many cracking experiences of light water reactor (LWR) core internals worldwide in the past. Thermal and Nuclear Power Engineering Society in Japan (TENPES) has organized a committee to prepare technically reasonable and appropriate inspection and evaluation guidelines (I&E guidelines) for core internals. This committee consists of scholars and representatives from electric utilities and nuclear plant vendors in Japan. I&E guidelines, which cover a rational inspection plan, structural integrity assessment and repair methods, have been developed considering nuclear safety function and structural strength of each core internal component. For BWR reactors, the development of I&E guidelines cover major core internal components like shroud support, core shroud, top guide, core plate, ICM and CRD housing, core spray piping and sparger, jet pump etc. For PWR reactors, the development of I&E guidelines cover baffle former bolts, barrel former bolts, core barrel weld, bottom mounted instrumentation, etc. The I&E guidelines will be completed by the end of March 2002. The basic concept of the guidelines, and a guideline for shroud support of a BWR as an example, are shown in this paper.

As the first developmental step of the sodium-cooled fast reactor (SFR) in China, the pool-type China Experimental Fast Reactor (CEFR) is equipped with the openings and inter-wrapper space in the core, which act as an important part of the decay heat removal system. The accurate prediction of coolant flow in the reactor core calls for complete three-dimensional calculations. In the present study, an investigation of thermal-hydraulic behaviors in a 180° full core model similar to that of CEFR was carried out using commercial Computational Fluid Dynamics (CFD) software. The actual geometries of the peripheral core baffle, fluid channels and narrow inter-wrapper gap were built up, and numerous subassemblies (SAs) were modeled as the porous medium with appropriate resistance and radial power distribution. First, the three-dimensional flow and temperature distributions in the full core under normal operating condition are obtained and quantitatively analyzed. And then the effect of inter-wrapper flow (IWF) on heat transfer performance is evaluated. In addition, the detailed flow path and direction in local inter-wrapper space including the internal and outlet regions are captured. This work can provide some valuable understanding of the core thermal-hydraulic phenomena for the research and design of SFRs.