A novel multi objective Loading Pattern Optimization by Gravitational Search Algorithm (GSA) for WWER1000 core

In this paper, a novel multi objective optimization algorithm, Gravitational Search Algorithm (GSA), is developed in order to implement in the Loading Pattern Optimization (LPO) of a nuclear reactor core. In recent decades several metaheuristic algorithms or computational intelligence methods have been expanded to optimize reactor core loading pattern. Regarding the coupled behavior of Neutronic and Thermal-Hydraulic (NTH) dynamics in a nuclear reactor core, proper loading pattern of fuel assemblies (FAs) depends on NTH aspects, simultaneously. Thus, obtaining optimal arrangement of FAs, in a core to meet special objective functions is a complex problem. Gravitational Search Algorithm (GSA) is constructed based on the law of Gravity and the notion of mass interactions, using the theory of Newtonian physics and searcher agents are the collection of masses. In this work, for multi objective optimization, the NTH aspects are included in fitness function. Neutronic goals include increasing multiplication factor (K_eff), decreasing of power picking factor (PPF) and flattening of the power density, also thermal–hydraulic (TH) goals include increasing critical heat flux (CHF) and decreasing average of fuel centers temperature. Therefore, at the first step, GSA method is compared with other metaheuristic algorithms on Shekel's Foxholes problem. In the second step for finding the best core pattern and implementation of the objectives listed, GSA algorithm has been performed for case of WWER1000 reactor. For the NTH calculations, PARCS (Purdue advanced reactor core simulator) and COBRA-EN codes are implemented, respectively. The results demonstrate that GSA algorithm have promising performance and can propose for other optimization problems of nuclear engineering field.     

Pitch-based ribbon-shaped carbon-fiber-reinforced one-dimensional carbon/carbon composites with ultrahigh thermal conductivity

Ribbon-shaped carbon fibers have been prepared from mesophase pitch by melt-spinning, oxidative stabilization and further heat treatment. The internal graphitic layers of ribbon-shaped carbon fibers graphitized at 2800 °C show a highly preferred orientation along the longitudinal direction. Parallel stretched and unidirectional arranged ribbon-shaped carbon fibers treated at about 450 °C were sprayed with a mesophase pitch powder grout, and then hot-pressed at 500 °C and subsequently carbonized and graphitized at various temperatures to produce one-dimensional carbon/carbon (C/C) composite blocks. The shape and microstructural orientation of ribbon fibers have been maintained in the process of hot-pressing and subsequent heat treatments and the main planes of the ribbon fibers are orderly accumulated along the hot-pressing direction. Microstructural analyses indicate that the C/C composite blocks have a typical structural anisotropy derived from the unidirectional arrangement of the highly oriented wide ribbon-shaped fibers in the composite block. The thermal conductivities of the C/C composites along the longitudinal direction of ribbon fibers increase with heat-treatment temperatures. The longitudinal thermal conductivity and thermal diffusivity at room temperature of the C/C composite blocks graphitized at 3100 °C are 896 W/m K and 642 mm²/s, respectively.     

A use of prototypic material for the investigation of severe accident progression

An experimental research platform using corium melts is established for the understanding of safety related important phenomena during a severe accident progression. The research platform includes TROI facility for corium water interaction experiments and VESTA facility for corium-structural material interaction experiments. A cold crucible technology is adapted and improved for a generation of 5–100 kg of corium melts at various compositions. TROI facility is used for experiments to investigate premixing and explosion behaviors during a fuel coolant interaction process. More than 70 experiments using corium at various compositions were performed to simulate steam explosion phenomena in a reactor situation. The results indicate that the conversion efficiency of steam explosion for corium is less than 1%. VESTA facility is used to investigate molten corium-structural material interaction phenomena. VESTA facility consists of two cold crucibles. One crucible is used for the melting of charged material and pouring of corium melt. The other crucible is used for the corium-structural material interaction while providing an induction heating to simulate the decay heat. The results of an experiment on the interaction between corium melt and a specimen made of Inconel performed in the VESTA facility is reported.     

Incorporating small fatigue crack growth in probabilistic life prediction: Effect of stress ratio in Ti–6Al–2Sn–4Zr–6Mo

The effect of stress ratio on the statistical aspects of small fatigue crack growth behavior was studied in a duplex microstructure of Ti–6Al–2Sn–4Zr–6Mo (Ti-6-2-4-6) at 260 °C with particular emphasis on incorporating small-crack data into probabilistic life prediction and the influence of stress ratio on probabilistic lifetime limits. A Focused Ion Beam (FIB) was used to machine micro-notches in test specimens, which served as crack-initiation sites and enabled the acquisition of multiple small-crack growth data sets from single experiment. Stress ratios of −0.5, 0.05, and 0.5 were employed, and small-crack growth was monitored by the acetate replication method. Qualitatively, change in the stress ratio produced almost negligible influence on the small-crack growth behavior when plotted as crack growth rate (da/dN) vs. applied stress intensity factor range (ΔK). A probabilistic method was employed to represent the variability in the small-crack growth behavior and the statistical differences with respect to stress ratio where a method of optimization of the small-crack growth model parameters, based on a minimization of the error between the predicted and the measured crack length vs. cycles (a vs. N) data, was used. In spite of qualitative similarity, differences in the statistical parameters of small-crack growth as a function of stress ratio were found to be significant in life prediction. The methods for representation and probabilistic treatment of small-crack data were also shown to be important factors in incorporation of the small-crack regime in probabilistic life prediction.     

Influence of loading levels on RCF life and failure mode of Ni-based alloy and WC–Ni ceramic composite coatings

This paper studied influence of loading levels on rolling contact fatigue (RCF) performance of NiCrBSi/WC–Ni composite coating. The results showed that abrasion, spalling, delamination, and rolling cracking were four kinds of main failure modes related with contact stress. Under relatively high contact stress, intense deformation of NiCrBSi particles resulted in rolling cracking failure. Furthermore, RCF life can be predicted by established lognormal distribution and σ_max − N model. The study also found that RCF life was closer to expectation E(N), higher failure probability of the coating. And RCF life became more discrete and more difficult to predict as contact stress increased.     

Incorporating carbon sequestration materials in civil infrastructure: A micro and nano-structural analysis

The Calera method for carbon sequestration promotes carbon mineralization through aqueous precipitation. This work reports a comprehensive analysis on a carbonate obtained by the Calera process to evaluate its suitability as a cement replacement for concrete applications. This work focuses on the analysis of two hydrated cement pastes made with a blend of Portland cement and Calera carbonates by various advanced analytical techniques. Scanning Electron Microscopy (SEM) equipped with Energy Dispersive Spectroscopy (EDS) was used to observe microstructures and determine elemental compositions. The synchrotron X-ray diffraction technique combined with Rietveld analysis were applied to identify constituent phases and refine crystal structures, crystallite sizes as well as relative phase abundances. Calcite and vaterite are observed in all samples while CSH II and portlandite are dominant in the cement pastes. Near-Edge X-ray Absorption Fine Structure (NEXAFS) spectrometry and Scanning Transmission X-ray Microscopy (STXM) experiments were conducted to investigate chemical speciation and morphological information of carbonate minerals with different absorption energies. STXM results confirmed heterogeneity of the samples, and also provided a nano-scale phase map across multiple particles. Differential Thermogravimetric (DTG) was used to observe heat transfer through structures and changes in mass upon heating. A compressive strength tests were performed on materials and shown comparable strength to Portland cement.     

高效铝合金圆铸锭均热炉的开发

通过对当前国内铝行业圆铸锭均热炉传统炉型优缺点的分析、比较，结合国外在该领域的发展趋势，对均热炉的炉型结构以及循环气流导流系统进行了研究及开发，并经过实际应用表明取得了良好的效果。     

Corrosion of the Heat-Affected Zones (HAZs) of API-X100 pipeline steel in dilute bicarbonate solutions at 90 °C – An electrochemical evaluation

This research explores for key correlations between the microstructures of API-X100 steel HAZs, simulated by Gleeble© thermal cycles, and their electrochemical corrosion behavior in dilute bicarbonate solutions at 90 °C. The potentiodynamic polarization revealed the role of ferrite of a HAZ cooled at 10 °C/s with the lowest passive currents, and those of acicular ferrite and martensite of the 30 and 60 °C/s HAZs with unstable, thin passivation. The 0.5 V vs. SCE potentiostatic currents suggested also a slow passivation growth, of repetitive breakdowns and repassivations, for the 30 and 60 °C/s HAZs. EIS equivalent circuits and time-dependent interfaces were proposed for each of the HAZ microstructures.     

An internal reformer for a pressurised SOFC system

A novel reformer design has been demonstrated that converts the methane required for a multi kilowatt SOFC stack. Results show the influence of temperature and the benefits of operating at elevated pressure on the reforming-catalyst fundamental reaction kinetics. Due to the high heat demand of the steam reforming reaction, efficient heat transfer between the SOFC stack and the reforming catalyst is essential. Parameters such as the volume/surface area ratio, choice of catalyst, and catalyst metal loading are key to the design, and these have been determined through a combination of computer modelling and experimental measurements. The thermal properties of the unit have been evaluated over a range of temperatures and fuel compositions that simulate system operating-conditions in the final product.     

Room-temperature creep behavior on crack tip of commercially pure titanium

The room-temperature creep behavior on crack tip of compact tensile (CT) specimen for commercially pure titanium (CP-Ti) was studied by experiment and finite element (FE) simulation in this paper. The experimental results indicated that the time-dependent deformation was observed on the crack tip of CP-Ti CT specimen at room temperature, which agreed with the primary creep, and crack propagation was not observed. In order to consider the creep behavior on crack tip, time-dependent J-integral was used to characterize the stress fields near crack tip. The room-temperature creep behavior on crack tip was analyzed by FE simulation, which was verified by experimental results. Then, the strain fields under different stress states were analyzed by FE simulation. The influences of the locations to crack tip and load on the room-temperature creep were analyzed, which shows that the creep significance on crack tip is enhanced with increasing of load and decreasing of distance to crack tip. The estimation formula of creep strain value along ligament direction of CP-Ti CT specimen was established and verified by FE simulation results.