Hasil untuk "Nuclear engineering. Atomic power"

Chong Shik Park

The Mu2e experiment at Fermilab requires acceleration and transport of intense proton beams in order to deliver stable, uniform particle spills to the production target. To meet the experimental requirement, particles will be extracted slowly from the Delivery Ring to the external beamline. Using Synergia2, we have performed multi-particle tracking simulations of third-integer resonant extraction in the Delivery Ring, including space charge effects, physical beamline elements, and apertures. A piecewise linear ramp profile of tune quadrupoles was used to maintain a constant averaged spill rate throughout extraction. To study and minimize beam losses, we implemented and introduced a number of features, beamline element apertures, and septum plane alignments. Dynamic bumps are also implemented for local orbit corrections in which septum entrance angles are controlled to reduce angular spreads of extracted beams.

M.M. Rahman, Muhammad Ruhul Amin, A.Z.Ziauddin Ahmed et al.

The threshold displacement energy (Ed) determines the quantity of defects generated through the minimum kinetic energy of a particle. Here, the displacement process of TaC is studied and hence the Ed is determined utilizing the ab-initio molecular dynamics simulation method. We use seven different crystallographic orientations, namely [100], [110], [111], [210], [211], [221], and [321] to observe the interaction between the primary knock-on atoms (PKAs) for both Ta and C. The computation of Ed values is taken between 16 eV and 50 eV. The weighted average Ed values are calculated from PKA orientations, which are found to be 42 eV for the Ta atom and 26 eV for the C atom. For Ta PKAs, anti-site defects are developed; however, they are not observed in the case of C PKAs. The collision mechanism is primarily influenced by the consecutive replacement collisions occurring along the [110] atomic row, resulting in a reduction of the Ed value in the crystallographic orientations. Finally, it is found that the Ed values play the role of creating the interstitial defects in the TaC.

DAI Tao, XU Longfei, LI Baiwen, SHEN Huayun, HU Yuan, MA Ruiyao

The discrete ordinates (SN) method proposed by Carlson constitutes an angular discretization for neutron transport equation. Owing to its superior computational accuracy and efficiency compared to alternative numerical approaches, the SN method has been extensively adopted in neutron transport applications, particularly in nuclear reactor design and radiation shielding optimization. Although the SN method demonstrates satisfactory performance and yields reliable results in most practical scenarios, it inherently suffers from ray effects, a well-documented numerical artifact that fundamentally limits its solution accuracy in the problems involving localized neutron source and wea scattering media. These angular discretization artifacts induce non-physical distortions in computed flux distributions, specifically generating artificial flux overestimations along preferential angular directions while suppressing flux magnitudes in geometrically unaligned regions. To address this defect, numerous of ray effect mitigation methods were developed. The virtual source method is formulated through the strategic introduction of pseudo-source terms into the SN equations, establishing equivalence with spherical harmonics (PN) formulations to eliminate ray effects. While this approach achieves angular flux correction by enforcing moment-matching conditions between SN and PN operators, its computational formalism becomes increasingly intricate due to higher-order spherical harmonic expansions, and suffers from convergence reliability concerns when handling multigroup problems with strongly anisotropic scattering coupling. The first collision source method, widely implemented in SN codes to mitigate ray effects, operates by employing alternative transport methodologies, such as ray tracing, Monte Carlo simulations, or PN expansions, to compute the uncollided flux component most severely impacted by ray effects, thereby reducing numerical distortions. However, this approach necessitates hybrid code architectures that integrate supplementary transport solvers with SN frameworks, substantially increasing computational complexity and programming challenges, while inheriting inherent limitations from the auxiliary methods: ray tracing struggles with reflective boundary conditions, Monte Carlo suffers from expensive computational costs, and PN method exhibit numerical oscillations in angularly anisotropic problems. In summary, ray effect severely constrains the computational accuracy of the SN method and have not yet been effectively resolved. In this paper, it is noticed that the SN method fundamentally constitutes a deterministic numerical integration scheme in angular dimension, whose characteristic ray effects arise from the inherent precision limitations of low-order angular quadrature techniques, particularly evident in non-smooth angular flux distributions with pronounced directional dependencies. Motivated by the capacity of Monte Carlo method to achieve precise integration of non-smooth functions, a novel random SN method based on quasi-Monte Carlo quadrature sets was proposed. Preliminary numerical results demonstrate that with equivalent numbers of discrete angular directions, the proposed method exhibits superior accuracy to conventional quadrature sets in strongly angularly anisotropic problems, but underperforms in weakly anisotropic scenarios. A collision-coupled rSN-SN methodology that synergistically integrates the advantages of stochastic and deterministic quadrature sets was further developed, with numerical verification confirming its capability to achieve enhanced computational precision at reduced computational time and resource expenditure compared to traditional implementations.

Ayman M. Sharaf, M.A. El-Nahal, Islam M. Nabil et al.

The present study aims to establish a new treatment method for removing or reducing the concentration of 226Ra and 228Ra in sludge waste produced due to natural gas production at natural gas processing Plants. The main radionuclides present in sludge waste of natural gas processing are Radium and its daughters due to their low solubility in the water they can form compounds with sulfate ions, carbonate ions, silicate ions, then precipitation scale or sludge. The suggested method is designed to be simple, applicable, economically beneficial, and environmentally safe, by using internal available resources like emitted hydrogen sulfide and sodium hydroxide, also reduction of chemicals that used in radioactivity treatment to be sulfuric acid or sodium hydroxide instead of multiple different chemicals that used in other treatment procedures. The effects of the used chemical reagents sulfuric acid and sodium hydroxide in various concentrations at different reaction temperatures on the sludge waste to extract the radium isotopes have been studied, evaluated, and compared. The study proved that removing radium isotopes is increased by elevating the reagents concentration and sludge temperature. The removal effects of the used reagents are approximately similar.

H. Wolter, M. Colonna, D. Cozma et al.

Transport models are the main method to obtain physics information from low to relativistic-energy heavy-ion collisions. The Transport Model Evaluation Project (TMEP) has been pursued to test the robustness of transport model predictions in reaching consistent conclusions from the same type of physical model. Calculations under controlled conditions of physical input and set-up were performed with various participating codes. These included both calculations of nuclear matter in a box with periodic boundary conditions, and more realistic calculations of heavy-ion collisions. In this intermediate review, we summarize and discuss the present status of the project. We also provide condensed descriptions of the 26 participating codes, which contributed to some part of the project. These include the major codes in use today. We review the main results of the studies completed so far. They show, that in box calculations the differences between the codes can be well understood and a convergence of the results can be reached. These studies also highlight the systematic differences between the two families of transport codes, known as BUU and QMD type codes. However, when the codes were compared in full heavy-ion collisions using different physical models, as recently for pion production, they still yielded substantially different results. This calls for further comparisons of heavy-ion collisions with controlled models and of box comparisons of important ingredients, like momentum-dependent fields, which are currently underway. We often indicate improved strategies in performing transport simulations and thus provide guidance to code developers. Results of transport simulations of heavy-ion collisions from a given code will have more significance if the code can be validated against benchmark calculations such as the ones summarized in this review.

LIU Feng1, ,  BAI Xujuan2,  SUN Zhongning1,  DING Ming1,  BIAN Haozhi1,

The condensation heat transfer of steam containing non-condensable gases is crucial for safety analysis in the event of severe accidents in the containment vessel. Previous studies have focused more on the heat transfer characteristics of condensation containing air, while less attention has been paid to the hydrogen-air conditions. The mechanism by which hydrogen migration affects condensation heat transfer is not yet clear. Numerical simulation methods were used to investigate the applicability of the multi-component diffusion coefficient equation under condensation phase change conditions in the paper. Based on experimental data, an effective steam diffusion correction model suitable for hydrogen-air conditions was proposed. Through the validation of experimental data from different scholars, 97% of predicted values have a relative deviation from experimental values maintained within ± 20%. Based on this, the hydrogen migration characteristics near the wall of the heat transfer tube and its effect on the condensation heat transfer coefficient were studied. The results indicate that there are three flow patterns of gas near the condensation surface, namely gravity flow, separation flow, and buoyancy flow. As the relative concentration of hydrogen increases, the gas flow pattern gradually changes from gravity flow to separation flow and buoyancy flow. The change in gas flow pattern will significantly affect the convective mass transfer rate of gas near the condensation surface, which has a stronger impact on condensation heat transfer than diffusion mass transfer. Ultimately, the condensation heat transfer coefficient shows a pattern of first decreasing and then increasing with the increase of relative hydrogen concentration. When the flow pattern of gravity flow is formed near the condensation surface, and an increase in the relative concentration of hydrogen gas will reduce the convective mass transfer rate of the gas near the condensation surface, while also increasing the diffusion mass transfer rate of steam in the mixed gas. The change in convective mass transfer rate plays a dominant role. Therefore, the condensation heat transfer coefficient will exhibit a negative correlation with the relative concentration of hydrogen gas. The condensation heat transfer coefficient is the lowest under the separated flow pattern. When a buoyancy flow is formed near the condensation surface, the convective and diffusive mass transfer rates of gas will increase with the relative concentration of hydrogen, and the heat transfer coefficient shows a positive correlation with the relative concentration of hydrogen. The study results are of great significance for evaluating the heat transfer characteristics of steam condensation after hydrogen release in serious accidents.

WANG Yimei1, , XIAO Qingshan1, CHEN Yinqiang1, LIU Tingguang2

Cast austenitic stainless steel (CASS) is widely used in the primary pipeline of pressurized water reactor nuclear power plants. Cast stainless steel will undergo thermal aging and embrittlement during long-term high-temperature service. CASS is actually composed of austenite and ferrite, and after long-term thermal aging, ferrite undergoes amplitude modulated decomposition, with the precipitation of G phase in the matrix. These are the main reasons for the embrittlement of CASS materials. During actual service, the main pipeline of the primary circuit not only bears the effects of long-term high-temperature thermal aging, but also bears the cyclic thermal and mechanical loads caused by startup and shutdown, reactor power fluctuations, and coolant flow, as well as the corrosion caused by the coolant of the primary circuit. These factors pose a risk of thermal aging and corrosion fatigue cracking in the main pipeline of the primary circuit. However, the impact of thermal aging on the performance of CASS mainly focuses on mechanical properties such as tension and impact, and there is relatively little research on the fatigue performance of CASS after thermal aging, especially in high-temperature and high-pressure water environments. Therefore, accelerated thermal aging tests were conducted at 400 ℃ of different periods on a typical nuclear power plant main pipeline material Z3CN20-09M, and the structure of the thermal aging samples was analyzed using transmission electron microscopy in this study. The fatigue life changes of Z3CN20-09M after thermal aging were studied in high-temperature air of 300 ℃ and simulated high-temperature and high-pressure water environment of the primary circuit to analyze the effect of thermal aging time on the fatigue behavior and life of Z3CN20-09M. The HRTEM results indicate that Z3CN20-09M undergoes lattice distortion on its (011) crystal plane after 5 000 hours of thermal aging. No amplitude modulated decomposition products, namely Fe rich α phase and Cr rich α' phase, were found in Z3CN20-09M after 5000 hours of thermal aging, and no G phase was found. The peak stress changes of Z3CN20-09M before and after thermal aging during cyclic loading are mainly divided into cyclic hardening stage and cyclic softening stage. After 1 000 hours of thermal aging, the fatigue life of Z3CN20-09M under high temperature air and simulated high-temperature and high-pressure water environment of the primary loop decreases slightly. As the thermal aging time extended to 5 000 hours, the fatigue life of Z3CN20-09M decreases. The ASME fatigue design curve still has sufficient safety margin for evaluating the fatigue life of Z3CN20-09M after thermal aging.

Doaa M. El Afandy, Eman M. Ibrahim, Ibrahim E. El Aassy et al.

The present study concerned with the activity concentrations of natural radionuclides (238U, 234U, 230Th, 226Ra, 232Th, 40K and, 235U) in ten sedimentary rock samples collected from fault zone, Gabal Um Hamd, southwestern Sinai, Egypt. These samples were investigated to study their behavior during a part of geologic time. The activity concentrations were measured using γ-ray spectrometry (HPGe detector). The investigated samples were analyzed for major oxides using the XRF technique. The results demonstrated high average activity concentrations of 238U, 234U, 230Th, 226Ra, 232Th, 40K and, 235U than the worldwide average values as reported by UNSCEAR 2008. Theil diagram showed that there are accumulation and leaching of uranium in some samples in the two sides of the fault zone. It is noticed that the ages of uranium depositions for the samples collected from the downthrown of the fault zone vary from 121.5 to 440.1 ky, while for the sample collected from the upthrown of the fault is 210.9 ky. The 230Th/232Th activity ratios range between 4.55 and 91.04 for downthrown samples and between 4.75 and 6.05 for upthrown samples which are smaller than 20 except for two samples, indicating a contamination of the samples by detrital 230Th. After subtraction of the detrital 230Th, the corrected ages for downthrown samples vary from 119.1 to 231.7 ky while for upthrown samples vary from 164.4 to 390 ky.

Vildan Ozkan Bilici

Ultrasonic testing (UT) is one of the most widely used non-destructive testing techniques for the characterization and evaluation of materials. In this study, the material properties of AstCrM-BN-Cr-Ti-Ni composites produced by mechanical mixing and electroless nickel plating technique were evaluated using UT. Changes in ultrasonic wave velocity, Young's modulus, density, porosity and hardness are observed in the heat-treated material at different temperatures. Samples analyzed by Scanning Electron Microscopy (SEM) and X-Ray Diffractometry (XRD) exhibited changes in grain structure at different sintering temperatures. It has been observed that the change in grain size also affects mechanical and physical properties according to ultrasonic properties. In conclusion, the experimental results showed a linear relationship between the mean grain size and the UT parameters (ultrasonic longitudinal and transverse velocity, Young's modulus), physical (sintering temperature and density) and mechanical properties (hardness and porosity) of the material. Grain growth occurs with increasing sintering temperature, porosity content decreases, hardness, Young's modulus and ultrasonic wave velocity values also increase.

Gaoxiang Wang, Shanliang Zheng, Chengming Qin et al.

An ion cyclotron resonance heating (ICRH) antenna will be installed in the equatorial port plug of the China Fusion Engineering Test Reactor (CFETR) for heating ions and electrons in plasma. This study reports the latest neutronic modeling and analyses of antenna for the subsequent optimization of the shielding design, with radiation damage, nuclear heating, gas generation of key components, and shutdown dose rate (SDDR) used as main indicators. Results showed that the nuclear heating of the BP was extremely high, thus posing a high risk to the structure, highlighting the necessity of further upgrading the shielding performance. In addition, the SDDR was more than 100 μSv/hr 12 days after the shutdown, rendering hands-on maintenance in the areas at a short time challenging. Meanwhile, key contributors to higher SDDR have been analyzed.

M. V. Supotnitskiy

Currently, there are practically no people left who have seen the consequences of the use of nuclear weapons. This is the reason for certain frivolous statements about the advisability of using tactical nuclear weapons to solve certain tactical problems. The purpose of this work is to remind, using the example of the consequences of the atomic bombings of the cities of Hiroshima and Nagasaki, how does the nuclear war looks like in reality. Materials and Methods. Open sources from the Cold War era and more recent reviews of the consequences of the use of nuclear weapons were analyzed. The analysis was carried out from general to specific, i.e. from the understanding of physical processes underlying a nuclear explosion and determining the design of the nuclear devices, to the specific consequences of their use. Discussion. The article analyses the history of the creation of the «Gadget», «Fat Man» and «Kid» bombs, their design, preparation and the results of the use. Detailed descriptions of nuclear explosions and the consequences of their use, made both by those who used nuclear weapons and by those against whom they were used, are provided. Being imperfect in design and ineffective in using fissile matter, they showed stunning power even for the present time, destroying two densely populated cities and at least 106 thousand people at once. Real examples show the features of the destruction of engineering objects and the impact on people of the damaging factors of a nuclear explosion. Attention is drawn to the fact that the power of the bombs used was 15 and 22 kt, respectively. According to modern NATO classification, these are tactical nuclear weapons. It is designed to destroy targets in the tactical depth of enemy troop deployment (up to 300 km). The maximum power of tactical ammunition according to NATO standards is up to 100 kt. It means that the yield of the tactical ammunition used in battle will depend on the tactical mission, and not be limited to a few kilotons. Conclusions. The use of tactical nuclear weapons without escalating their power, causing large casualties among the population and the risk of being drawn into a global nuclear war is impossible. Currently, the world is oversaturated with nuclear and thermonuclear weapons. Some countries possess them secretly, others have the potential to create such weapons. Therefore, any use of nuclear weapons by anyone will lead to the lowering of the threshold of nuclear deterrence. It will become a common thing during the resolution of military conflicts.

Hikari Sato, Ryo Saga, Fumio Komai et al.

Purpose: Radiation dermatitis is a common adverse event in radiotherapy and is treated using topical agents or dressings; however, it may be exacerbated by increasing the skin dose during irradiation. This study investigated the effects on the dose and dose distribution assuming irradiation without wiping the agent off. Methods: Five types of topical products and dressings available in clinical settings were used in this study. These products were applied to a tough water phantom, and the dose and dose distributions of photon and electron beam were measured using an ionization chamber and an EBT3 Gafchromic film, respectively. For dose measurements, topical products were applied to thicknesses of 0, 1, 2, 3, 4, 5, and 10 mm, and 100 monitor units (MU) were irradiated. The dressings were pasted onto the phantom. For dose distribution measurements, the Gafchromic film was placed parallel to the radiation flux. The thicknesses of the topical products were 0, 1, and 5 mm. Results: The doses of 6 and 10 MV X-rays increased 0.35–0.82% and 0.25–0.55% with topical product thicknesses of 4 or 5 mm, respectively. In contrast, the electron beam dose decreased by 10.67% at 6 MeV and 2.11% at 12 MeV with a topical product thickness of 5 mm. The applied topical products shifted the X-ray and electron beam dose distributions toward the surface. However, the dressings did not affect the dose and dose distributions. Specifically, dose changes were less than 0.3% for all employed dressings. Conclusion: Based on the results of this study, we suggest that topical agents and dressings do not affect the dose and dose distribution except when topical agents are applied particularly thickly. However, the actual dose received by the skin needs to be investigated in the future.

G. Verdoolaege, S. Kaye, C. Angioni et al.

The multi-machine International Tokamak Physics Activity (ITPA) Global H-mode Confinement Database has been upgraded with new data from JET with the ITER-like wall and ASDEX Upgrade with the full tungsten wall. This paper describes the new database and presents results of regression analysis to estimate the global energy confinement scaling in H-mode plasmas using a standard power law. Various subsets of the database are considered, focusing on type of wall and divertor materials, confinement regime (all H-modes, ELMy H or ELM-free) and ITER-like constraints. Apart from ordinary least squares (OLS), two other, robust regression techniques are applied, which take into account uncertainty on all variables. Regression on data from individual devices shows that, generally, the confinement dependence on density and the power degradation are weakest in the fully metallic devices. Using the multi-machine scalings, predictions are made of the confinement time in a standard ELMy H-mode scenario in ITER. The uncertainty on the scaling parameters is discussed with a view to practically useful error bars on the parameters and predictions. One of the derived scalings for ELMy H-modes on an ITER-like subset is studied in particular and compared to the IPB98(y, 2) confinement scaling in engineering and dimensionless form. Transformation of this new scaling from engineering variables to dimensionless quantities is shown to result in large error bars on the dimensionless scaling. Regression analysis in the space of dimensionless variables is therefore proposed as an alternative, yielding acceptable estimates for the dimensionless scaling. The new scaling, which is dimensionally correct within the uncertainties, suggests that some dependencies of confinement in the multi-machine database can be reconciled with parameter scans in individual devices. This includes vanishingly small dependence of confinement on line-averaged density and normalized plasma pressure (β), as well as a noticeable, positive dependence on effective atomic mass and plasma triangularity. Extrapolation of this scaling to ITER yields a somewhat lower confinement time compared to the IPB98(y, 2) prediction, possibly related to the considerably weaker dependence on major radius in the new scaling (slightly above linear). Further studies are needed to compare more flexible regression models with the power law used here. In addition, data from more devices concerning possible ‘hidden variables’ could help to determine their influence on confinement, while adding data in sparsely populated areas of the parameter space may contribute to further disentangling some of the global confinement dependencies in tokamak plasmas.

L. Chkhartishvili, Shorena Dekansidze

A mini-review on obtaining methods of boron carbide based titanium-containing nanocomposite materials is presented. Due to their unique physical-mechanical properties, such materials have a wide field of technological applications. Boron carbide-based ceramic materials are actively used in machine-building, nuclear power engineering, and ballistic armor production as well. This is due to the boron carbide unique physical-mechanical properties: high hardness, high melting point, and high modulus of elasticity, as well as high wear-, corrosionand radiation-resistances, etc. In addition, boron carbide has the ability to absorb or transmit thermal neutrons depending on boron-isotopic composition since the capture cross sections of thermal neutrons by boron stable isotopes 10B and 11B differ from each other too significantly – by seven orders of magnitude. Among the currently used in technologies hard materials, boron carbide has the highest hardness-todensity ratio [1]. These properties make boron carbide attractive for the manufacture of abrasives and grinding materials, friction pairs in moving parts and machine units working in extreme environments and also nozzles for surface treatment with fluid abrasives, protective coatings (in particular, for the boronizing of steels and refractory metals), light ballistic armors, synthesis of nuclear industry materials (for example, manufacture of the nuclear reactors control rods), neutron detectors; etc. Besides, there are developed various boron carbide-based thermoelectric converters, boron-carbide/graphite thermocouples, as well as nonlinear resistors. But, at the present time despite its attractive electronic properties boron carbide as a semiconductor material is used relatively rarely. The point is that the preparation of samples of sufficient for this purpose purity is associated with additional difficulties. As for the superhard boron carbide based composite materials, they can be used for manufacturing indenters and tools for processing other solid materials, and the like. However, the field of possible applications of boron carbide is significantly narrowed due to its brittleness and low stability against the cracks formation. Today, materials science Obtaining of boron carbide based titanium-containing nanocomposites (Mini-review). 8 DOI: 10.6084/m9.figshare.13850393 with these disadvantages is struggling with the creation of nanocrystalline structures of heteromodular, quasibinary, and multicomponent boron carbide based ceramic and/or metalceramic materials. As is known, in general the creation of materials with nanostructure laid the foundation for the development of a new class of materials with unique complexes of properties. But, for boron carbide based materials in this direction significant results have not been achieved yet. Therefore, it is interesting to establish how physical-chemical and physical-mechanical properties, and also the performance characteristics of these materials are changed in the transition from crystalline state to nanocrystalline state by varying their morphological parameters. Heteromodular ceramics successfully combine a high-modulus ceramic matrix with additional components in form of particles or fibers with a much lower modulus of elasticity. In other words, in these materials, the hardness and wear resistance of the ceramic matrix are combined with the impact strength and ductility of binder metal or alloy. It is known that brittle compounds such as carbides, nitrides, and part of borides are characterized by low thermal stability and impact strength and these characteristics can be improved by adding lowmodular phases in matrix. In the seminal work [2], on the basis of continuous medium and micromechanics theories it was shown how it is possible to significantly improve the properties of the high-temperature structures with low stability against thermal stresses by introducing the dispersed phases with low modulus of elasticity. The high stability of heteromodular ceramics against to external influences is due to the peculiarity of easy absorption and/or transmission of energy released during the formation of cracks in their structure. In addition, they effectively dig up the front of the developing crack and / or divert it from the initial direction of propagation. The creation of a boron carbide based heteromodular material is possible if: – the starting material is finely dispersed, and – the good adhesion of the metal binder to the boron carbide surface is combined with its low chemical reactivity. So, to create effective boron carbide based nanocomposites, it is essential to know how to manipulate by the mechanically and thermally separating surfaces. If the assembling of the ceramic component (i.e. boron carbide) is carried out in the nanocrystalline state, the physicalmechanical properties of the material will be qualitatively improved. This is because the contribution of the surface layers will be decisive in the energy balance of the system. Under these conditions, the spectrum of atomic vibrations will change radically affecting diffusion and, in general, all the transport phenomena. Accordingly, the quality of adhesion relative to passive components will be also improved significantly. An additional obstacle to the wider application of the boron carbide attractive properties is the complexity of the compacting of its powders. To this day, the main approach to the obtaining sufficiently dense samples of boron carbide based materials is their high-temperature (above 2000 °C) pressing. However, in this way it is possible to obtain only samples of small sizes and simple geometric shapes. At such temperatures the process of agglomeration of the boron carbide crystallites is rather intense. Accordingly, the preservation of the nanostructure in consolidated samples is complicated and the quality of the material is deteriorated. Proceeding from this, it seems expedient to search for such assembling processes of boron carbide based nanocomposites, which will be carried out at relatively moderate temperatures. L. Chkhartishvili & Sh. Dekanosidze. Nano Studies, 2020, 20, 7-18. DOI: 10.6084/m9.figshare.13850393 9 Creation of boron carbide based quasibinary and multicomponent ceramic nanosystems will allow maintaining high hardness of this material simultaneously improving its toughness and maximizing the sintering temperature, which will ensure the creation of large-sized machine parts and units of complex shapes. From number of boron carbide-based ceramic and metalceramic systems, the most promising, respectively, are titanium-containing metal alloys and boron carbide alloys with titanium diboride TiB2: B4C–TiB2. This paper presents a mini-review of developments in technologies for their obtaining. Methods for preparing eutectic alloys of boron carbide and titanium diboride B4C–TiB2 are widely known. An example of obtaining a eutectic B4C–TiB2 alloy was presented in [3]. This composite was also obtained in situ by consolidation directly from a mixture of powdered components [4]. In particular, the material containing 10 – 40 % of TiB2 was obtained by reacting B4C, TiO2, and C (graphite) powders with the traditional sintering method at a temperature of > 2000 °C and a pressure of 35 MPa. In this case, the TiB2 nanosized particles are located both within B4C matrix grains and at their boundaries as well. Also the spark-plasma synthesis was used for hot pressing [5]. By the combination of pressing with reaction-synthesis, it is possible to reduce the consolidation temperature by 200 – 400 °C [6]. But, it still remains quite high. The B4C–TiB2 eutectic powder composite was prepared [7] by plasma treatment using a mixture of B4C and TiB2 powders for starting materials. This mixture was fed by argon flow in the plasma discharge region, where its components were fused. The powder passed through the plasma contains crystals both of B4C and TiB2 and additional phase of boron oxide B2O3. In relatively large-sized particles (above 10 μm), a plate-structured eutectic was observed, where the phases separation ranges from 100 to 650 nm. A common disadvantage of the abovementioned technologies is that they are not able to provide product in a nanocrystalline structure. In the literature, one can find extensive information on such boron carbide based materials, which contain different (usually metallic) additional elements, their oxides, borides and other compounds: Al [8 – 11], Cr [12 – 14], Fe [15 – 19], Hf [20], Mo [21, 22], Nb [22, 23], Ni [14, 17, 24, 25], Sc [12, 26], Si [9, 21, 27 – 45], etc. Bearing in mind the main purpose of this review, below we consider only titanium compounds containing composites. The B4C–TiB2–TiO2 ceramics obtained by hot pressing of the B4C–TiO2–C charge were studied in [46]. The addition of TiO2 helps hot pressing to obtain a heterophase boron carbidebased material [27]. It activates the sintering process and allows the creation of ceramic materials of the B4C–TiB2 system. The effect of the addition of B4C, (Ti,Cr)C and P on the kinetics of oxidation in air under isothermal heating was studied by the thermogravimetric method [14]. The effect addition of aluminum together with titanium on kinetics of compaction, structure and properties of the materials of B4C–(Ti–Al) system was also studied [47]. In [48], the reaction of boron carbide with titanium carbide was investigated under various conditions. Reactive sintering of the starting mixtures passing through the stage of lower boride formation gives the heterophase material B4C–TiB2. The concentration of the reaction product, adiabatic temperatures, and other thermal characteristics in the Ti–B4C system containing 99 wt. % B4C were determined using thermodynamic analysis [49]. For the production of alloys of titanium with its boride and carbide using selfpropagating high-temperature synthesis, the composition of the appropriate mixture was Obtaining of b

Jiong Guo, Yizhen Wang, Han Zhang et al.

Abstract There has been increasing demand for uncertainty quantification (UQ) in the nuclear engineering community. Thus far, most uncertainty analyses have focused on light water reactor (LWR). As an innovative reactor, the pebble-bed high-temperature gas-cooled reactor (PB-HTGR) features a continuous-fuel-cycling operation strategy and a movable core, which means the uncertainty analysis methods used for LWRs cannot be directly applied to the PB-HTGR. In this work, we summarize recent progress in the uncertainty analysis of the PB-HTGR at the Institute of Nuclear and New Energy Technology, Tsinghua University. We propose a framework for uncertainty analysis based on the well-developed, practical design of the PB-HTGR program system. In this framework, the uncertainty sources are divided into different components and steps, and the maximum fuel temperature in a depressurized loss of forced cooling accident is chosen as the final uncertainty output parameter. However, not all the issues are resolved as this system involves a complex combination of many physical and thermal factors. To date, within this framework, several milestones have been achieved in the PB-HTR uncertainty analysis. (1) We have developed the uncertainty analysis tool VSOP-UAM (very superior old program–uncertainty analysis in modeling), which uses a statistical sampling method. Using VSOP-UAM, we have achieved the uncertainty analysis of the equilibrium state, which is the typical state of the PB-HTGR, for the first time. (2) Using the VSOP-UAM analysis tool, we have determined the uncertainty propagation of the nuclear cross-section data, fission product yields, and key structural parameters. (3) To determine the UQ of the fission product yields, we developed an advanced sampling method that prevents the sampling of non-physical negative samples. (4) To facilitate a benchmark definition and UQ for the PB-HTGR, studies have also been conducted under the auspices of the Coordinated Research Project on High-Temperature Gas-Cooled Reactor Uncertainty Analysis in Modeling, launched by the International Atomic Energy Agency.

Okorie Ukairo, S. Dembélé, A. Heidari et al.

The outbreak of fires in nuclear power plants is a major risk due to the potential leak of radioactive materials. The use of traditional prescriptive fire safety regulations has shown its limitations and there is now a shift towards performance-based fire safety engineering, which requires well-validated fire models. Nuclear power plants require the use of mechanical ventilation, which provides dynamic confinement for nuclear materials by maintaining the required pressure. The occurrence of fires could potentially result in pressure variations within power plants. Although dynamic confinement along with other safety measures are in place to prevent fires, there is a continuous need to assess fire safety measures and reduce the risk of fire propagation with the use of fire simulation codes. The current study aims to build on existing research by making use of an emerging open-source computational fluid dynamics (CFD) fire simulation code known as FireFOAM, to predict fire behaviour in a mechanically ventilated nuclear compartment. An existing in-house modified version of FireFOAM developed by the authors’ research group, is further modified in the present work to include a Conjugate Heat Transfer (CHT) model to account for the heat transfer between combustion gases and solid boundaries. The CHT is validated using the experimental wall temperatures and heat fluxes. Furthermore, a mechanical ventilation model has been developed and implemented into FireFOAM. This newly modified version of FireFOAM is employed to predict the pressure variations in a nuclear compartment and the flow rates in the ventilation network. The predictions are compared to some experimental data from the open literature. Overall, it is shown that the mechanical ventilation model and the modified FireFOAM with CHT can predict the pressure variations and flow rates with a relatively good level of accuracy. derived from the subgrid-scale quantities. The combustion model assumes infinitely fast chemistry to control the filtered reaction rate by turbulent mixing rate between the fine structures located at Kolmogorov scales and the surrounding fluids. The turbulence model used is the one equation eddy viscosity model (Menom et al., 1996) for sub-grid scale closure.

Xiaoping Yang, Pengfei Fu, N. Chen et al.

Abstract The direct contact condensation (DCC) of submerged vapor jet in liquid, which has high heat and mass transfer efficiency, is widely applied in nuclear power generation, chemical engineering and aerospace. The pressure pulse generated by hydraulic instability during DCC may create periodical impulsive loads on the solid wall. It is important to evaluate pressure pulse characteristics using a wide range of inlet properties to avoid risky flow pattern regions where pressure pulses are strong. This paper presents an experimental study of the interface dynamics and pressure pulse of DCC using subsonic and supersonic steam jets condensing in water in a horizontal channel. The results reveal that pressure pulses in unstable region are caused by the contraction and expansion of the steam-water interface, while pressure pulses in stable region are caused by Kelvin-Helmholtz (KH) instability. Flow pattern transition is found to affect pressure pulse intensity. Pressure pulse intensity is minimal at the transition between the stable region and unstable region. The correlations of pressure pulse intensity in unstable and stable regions are given, respectively. The results of this study can inform the design, safe operation, and lifespan evaluation of equipment in various industrial applications that involve DCC.

B. Aygün, E. Şakar, Vishwanath P. Singh et al.

Abstract In this study, 12 different concentrations of shielding materials were developed and produced. They were covered with high temperature resistant (1500 °C) sodium silicate sealing paste. Epoxy resin was produced by adding different percentages of additive materials such as chromium oxide (Cr2O3), lithium (LiF), and nickel oxide (NiO). The GEANT4 and FLUKA codes of the Monte Carlo simulation toolkit were used to determine the mixing ratios. The total macroscopic cross-sections, effective removal cross-sections, mean free path, half value layer, and transmission neutron number were determined for fast neutron radiation using GEANT4 and FLUKA simulation codes. The mass attenuation coefficient, the effective atomic number and half-value layer (HVL) of the samples were calculated using Phy-X/PSD software. The absorbed dose was measured. In this study, an 241Am–Be neutron source with 74 GBq activity and average neutron energy of approximately 4.5 MeV and a BF3 gas detector were used. Both simulation and experimental measurements were compared with paraffin and conventional concrete. The new composite shielding material absorbed radiation much better than the reference materials. This new radiation shielding composite material can be used in nuclear medicine, transport and storage of radioactive waste, nuclear power plants, and as a shielding material for neutron and gamma radiation.

Zhongliang Xie, N. Shen, Wei-dong Zhu et al.

Abstract The research explores rotor dynamics characteristics and dynamic responses of Sodium bearing rotor coupled system fast reactor two-circuit main loop liquid sodium pump system in the nuclear power station. Natural frequency and vibration modes are given, vibration amplitude at the key point of support position are extracted. Through the analysis, rotor-dynamic properties and performances of the rotor system are given. With regard to different operating and initial conditions, the rotor-dynamic characteristics are investigated. Extreme operation conditions are also analyzed. Analysis shows that the structure design of sodium bearing as well as the bearing-rotor coupled system are reasonable and reliable, which can fully meet the technical requirements. Results indicate that it has certain guidance for the design of special engineering bearing-rotor system.

A. Tayebi, H. Bezzout, M. El Maghraoui et al.

In this work, an efficient algorithm, using a finite-difference time-domain (FDTD) technique, is proposed for modeling the variation of radon concentration as a function of soil structure parameters and vice versa. The development of the FDTD model is based on the simultaneous resolution of the radon transport equation in a porous, homogeneous medium, namely the soil. This equation describes the concentration of radon per pore volume unit. The numerical results are compared with those of the literature or with the theoretical ones.