Transient thermal hydraulic modeling and analysis of ITER divertor plate system

A mathematical model has been developed/updated to simulate the steady state and transient thermal-hydraulics of the International Thermonuclear Experimental Reactor (ITER) divertor module. The model predicts the thermal response of the armour coating, divertor plate structural materials and coolant channels. The selected heat transfer correlations cover all operating conditions of ITER under both normal and off-normal situations. The model also accounts for the melting, vaporization, and solidification of the armour material. The developed model is to provide a quick benchmark of the HEIGHTS multidimensional comprehensive simulation package. The present model divides the coolant channels into a specified axial regions and the divertor plate into a specified radial zones, then a two-dimensional heat conduction calculation is created to predict the temperature distribution for both steady and transient states. The model is benchmarked against experimental data performed at Sandia National Laboratory for both bare and swirl tape coolant channel mockups. The results show very good agreements with the data for steady and transient states. The model is then used to predict the thermal behavior of the ITER plasma facing and structural materials due to plasma instability event where 60 MJ/m² plasma energy is deposited over 500 ms. The results for ITER divertor response is analyzed and compared with HEIGHTS results.     

Prediction of transpiration effects on heat and mass transfer by different turbulence models

The paper reports the results of a study related to transpirating flows, stimulated by the interest that these phenomena, occurring in the presence of simultaneous heat and mass transfer, have for nuclear reactor applications. The work includes a summary and the follow-up of previous experimental and numerical investigations on filmwise condensation and falling film evaporation and of a recent review of different forms of the heat and mass transfer analogy. The particular objective here pursued is to compare transpiration effects as predicted by different turbulence models with classical suction and blowing multipliers based on stagnant layer theories, in the attempt to clarify their quantitative implications on the predicted mass transfer rates.A commercial and an in-house CFD code have been adopted for evaluating the heat and mass transfer rates occurring over a flat plate exposed to an air-vapour stream, with uniform bulk steam mass fraction and temperature boundary conditions at the wall. This simple configuration was purposely selected since it is a simplified representation of the test section of an experimental facility presently in operation at the University of Pisa. This allows a direct comparison between the heat and mass transfer coefficients predicted by CFD models and classical correlations for Nusselt and Sherwood numbers.     

Sample analysis of masterpieces and archaeological materials by nuclear microprobe: Principle,possibilities, preliminary results

The physico-chemical characteristics of the pigments used in oil paintings supply valuable informations concerning the age of the work and sometimes even the geographic origin of the ores used.After a review of the working principles of the nuclear microprobe and its analytical possibilities, the first results obtained by microanalysis of paint sections with the aim of nondestructive impurity content analysis of the white lead are presented.     

Theoretical analysis of mass transfer and reaction in a porous medium applied to the gasification of graphite by water vapor

The theories of mass transfer and reaction in porous medium were applied to investigate the gasification of graphite by water vapor in reactor. Based on several logical assumptions, the gasification of graphite by water vapor was investigated. Different shapes of graphite were analysed: semi-infinite blocks, planks and cylinders. Analysis reveals that the reaction rate varies with the location, which can explain the intense gasification that occurs at upstream during experiments. The temperature dependence of the reaction rate expressed different ranges. At low temperatures, the reaction rates depend greatly on the reaction temperature, and the influence of shape is more pronounced. At high temperatures, the dependence weakens due to the limit of gas transfer, and the influence of shape disappears. The water vapor pressure at exterior surface decreases with temperature, but the pressure gradients (both inside and outside of porous media) increases with temperature. For the platelike and cylindrical porous media, the reaction rate decreases with the thickness or radius because of the increase in specific surface. When the penetrating depth of water vapor is larger than the half-thickness or radius of porous media, the water vapor would cumulate in porous media so that the pressure of reacting gas increases.     

Separation of potential and kinetic electron emission from Si and W induced by multiply charged neon and argon ions

The total secondary electron emission yields, γ_T, induced by impact of the fast ions Ne^q+ (q = 2-8) and Ar^q+ (q = 3-12) on Si and Ne^q+ (q = 2-8) on W targets have been measured. It was observed that for a given impact energy, γ_T increases with the charge of projectile ion. By plotting γ_T as a function of the total potential energy of the respective ion, true kinetic and potential electron yields have been obtained. Potential electron yield was proportional to the total potential energy of the projectile ion. However, decrease in potential electron yield with increasing kinetic energy of Ne^q+ impact on Si and W was observed. This decrease in potential electron yield with kinetic energy of the ion was more pronounced for the projectile ions having higher charge states. Moreover, kinetic electron yield to energy-loss ratio for various ion-target combinations was calculated and results were in good agreement with semi-empirical model for kinetic electron emission.     

A study of fuel behavior in PWR design basis accident: an analysis of results from the PHEBUS and EDGAR experiments

As part of the French PWR safety study programme, fuel behavior during a design basis accident has been investigated in three parallel directions:

• - separate effect tests in the EDGAR apparatus for developing and validating cladding deformation models,

• - integral tests in PHEBUS for verifying codes,

• - development of fuel behaviour codes for plant calculation after assessment against experimental results. After describing the objectives and content of each of these programmes, the main findings are highlighted and discussed.

Accuracy improvement of quantitative analysis of calorific value of coal by combining support vector machine and partial least square methods in laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy(LIBS) is a potential technology for online coal property analysis,but successful quantitative measurement of calorific value using LIBS suffers from relatively low accuracy caused by the matrix effect.To solve this problem,the support vector machine(SVM) and the partial least square(PLS) were combined to increase the measurement accuracy of calorific value in this study.The combination model utilized SVM to classify coal samples into two groups according to their volatile matter contents to reduce the matrix effect,and then applied PLS to establish calibration models for each sample group respectively.The proposed model was applied to the measurement of calorific values of 53 coal samples,showing that the proposed model could greatly increase accuracy of the measurement of calorific values.Compared with the traditional PLS method,the coefficient of determination(R2) was improved from 0.93 to 0.97,the root-mean-square error of prediction was reduced from 1.68 MJ kg~(-1) to1.08 MJ kg~(-1),and the average relative error was decreased from 6.7% to 3.93%,showing an overall improvement.     

Observation and analysis of defect structure evolution from radiation damage by D-T fusion neutrons

A previous report on the defect structure evolution in metals, alloys and other materials by D-T fusion neutron irradiation (J. Nucl. Mater. 133&134 (1985) 85) was not accompanied with figures and illustrations, and they are all presented in this paper. More than half of the figures consists of electron micrographs, including the following: disordered zones to show the flight distances of interstitial atoms, amorphous zones in a semiconductor, grouped defect clusters developed from sub-cascade damage, stereo-micrographs of three dimensional configurations of defect clusters in sub-cascade groups, variation of defect structures with irradiation temperature, comparison of defect structures developed in thin foil and bulk specimens to demonstrate the role of free interstitials, homogeneous and localized formation of interstitial clustered defects, detection of invisible defects by the aid of electron illumination, and dislocation structures introduced by the deformation of irradiated materials. The other figures contain numerical results of micrograph analysis, which can be used for the estimation of neutron collision cross-section and primary knock-on energy. Point defect processes occurring during the damage structure evolution, including the dynamical effect of collisions, are discussed on the basis of experimental observations.     

Measurements and analysis of transmitted spectra from LOTUS fission-suppressed hybrid blanket driven by D-T neutrons

The neutron spectra transmitted across a fission-suppressed hybrid blanket and its components, driven by a low intensity 14 MeV Haefely neutron generator, were measured with a 2×2 NE213 detector at LOTUS facility. These experiments have been analyzed with 2D and 3D codes DOT3.5 and MCNP, respectively. The spectral integrals between 15 to 1 MeV show good agreement among the 2D, the 3D, and the NE213 for 15 cm lead, 18 cm beryllium, and 25 cm graphite slabs. However, there are large discrepancies for 6.2 cm stainless steel and 15 cm lithium carbonate slabs. The assemblies involving two or more of these slabs reflect these tendencies. We observe also considerable disagreement over pointwise spectra for a number of assemblies.Work done while on visiting assignment to Institut de Génie Atomique, E.P.F.L.     

Heat transfer from a high temperature safety rod placed in a perforated guide tube and surrounded by an array of cold tubes

In this paper, a simple natural convection heat-transfer model for a safety rod placed in a perforated guide tube is proposed. The geometry is typical of the Savannah River K reactor. The proposed model for the rod and the perforated guide-tube assembly is benchmarked against prototypical test data obtained by Idaho National Engineering Laboratory. The results showed that the proposed model was in good agreement with the experimental data except at very high temperatures where the model slightly underpredicted the rod and tube temperatures. By evaluating the thermal conductivity of the fluid (air) at the wall temperature, the prediction of the high temperature natural convection data was further improved.     

Characterization of pre-Hispanic pottery from Teotihuacan, Mexico, by a combined PIXE–RBS and XRD analysis

A combined analysis of IBA techniques (Proton Induced X-ray Emission (PIXE) and Rutherford Backscattering Spectroscopy (RBS)) and a complementary study by X-ray Diffraction (XRD) were performed to characterize pottery corresponding to the Epiclassic period (A.D. 700–900) from Teotihuacan, Mexico. Elemental compositions of pottery samples were measured by simultaneous PIXE and RBS using 2.6 MeV protons. Red, white and brown pottery pigments were studied by non-vacuum PIXE and a proton beam of 3 MeV. The various mineralogical phases of the pottery were identified by XRD. From pottery elemental compositions and its mineralogical phases, some differences among the pottery samples and groups were established.     

Comparison of inter-diffusion coefficients for Ni/Cu thin films determined from classical heating analysis and linear temperature ramping analysis by means of profile reconstruction and a numerical solution of Fick’s law

Classical inter-diffusion studies assume a constant time of annealing when samples are annealed in a furnace. It is assumed that the sample temperature reaches the annealing temperature immediately after insertion, while the sample temperature immediately drops to room temperature after removal, the annealing time being taken as the time between insertion and removal. Using the above assumption, the diffusion coefficient can be calculated in a number of ways. In reality, the sample temperature does not immediately reach the annealing temperature; instead it rises at a rate governed by several heat transfer mechanisms, depending on the annealing procedure. For short annealing times, the sample temperature may not attain the annealing temperature, while for extended annealing times the sample temperature may reach the annealing temperature only for a fraction of the annealing time. To eliminate the effect of heat transfer mechanisms, a linear temperature ramping regime is proposed. Used in conjunction with a suitable profile reconstructing technique and a numerical solution of Fick’s second law, the inter-diffusion parameters obtained from a linear ramping of Ni/Cu thin film samples can be compared to those obtained from calculations performed with the so-called Mixing-Roughness-Information model or any other suitable method used to determine classical diffusion coefficients.