04/01595 BWR fuel reloads design using a Tabu search technique: Castillo, A. et al. Annals of Nuclear Energy, 2004, 31, (2), 151–161

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16 Fuel science and technology (fundamental science, analysis, instrumentation) reference components in liquid fuels and surrogate blends. A lumped approach is used to reduce the complexity of the overall scheme in terms of species and reactions. Particular attention is devoted to the role of the isomerization or internal abstraction of H atoms in competition with ~-decomposition ones. Primary oxidation and decomposition reactions of the cyclohexyl radical are discussed to explain and justify this lumping procedure. The modelling predictions are compared with different sets of measurements. The validation of the low temperature oxidation mechanism of cyclohexane is based on the ignition delay times obtained both in the rapid compression machine at Lille and in closed vessels. Jet-stirred reactors at different pressures and stoichiometric ratios also confirm the reliability of the overall mechanism of oxidation. The comparisons between the model's predictions and the measurements relating to the pyrolysis and oxidation of methylcyclohexane in the Princeton turbulent flow reactor further support this extension of the kinetic scheme to naphthenes. Finally, the agreement with the oxidation experiments using mixtures of toluene + methylcyclohexane is a primary and simple example of the model's ability to deal with the combustion of real fuels or surrogate blends. 04/01589 Accuracy of reflectance analysis of coals Artser, A. S. et al. Koks i Khimiya, 2003, 2, 2-9. (In Russian) This article deals with quantity evaluation of accuracy of reflectance analysis of coals. 0401590 An application of the 'end-point' method to the minimum critical mass problem in two group transport theory Williams, M. M. R. Annals of Nuclear Energy, 2003, 30, (17), 1707- 1729. A two group integral equation derived using transport theory, which describes the fuel distribution necessary for a flat thermal flux and minimum critical mass, is solved by the classical end-point method. This method has a number of advantages and in particular highlights the changing behaviour of the fissile mass distribution function in the neighbourhood of the core-reflector interface. The paper also shows how the reflector thermal flux behaves and explains the origin of the maximum that arises when the critical size is less than that corresponding to minimum critical mass. A comparison is made with diffusion theory and the necessary and somewhat artificial presence of surface delta functions in the fuel distribution is shown to be analogous to the edge transients that arise naturally in transport theory. 04/01591 An artificial intelligence treatment of devolatilization for pulverized coal and biomass in co-fired flames Abbas, T. et al. Combustion and Flame, 2003, 132, (3), 305-318. Coal is complex and heterogeneous, with extremely variable properties. As a result, it has proved very difficult to construct generalized physical descriptions of pulverized coal combustion for incorporation into reliable mathematical models suited to industrial applications. There are many processes to be simulated: pyrolysis, char kinetics, particle/ turbulence interaction, etc. This paper is concerned with the early stages of pyrolysis, which significantly affect flame stability, NO formation, soot formation, and ultimately, char burn-out. In most of the existing predictive procedures for devolatilization, combustion and emissions are modelled by a single-step global chemical reaction, with the yield of volatile matter presumed to experience mixing-controlled combustion. Several more detailed multi-step coal devolatilization models have recently emerged, having a range of capabilities, e.g. predicting the thermal decomposition of a coal under practical conditions. A common shortcoming of these models is that they require a large set of input data, involving kinetic parameters, gas precursor compositions, and additional parameters describing the coal's polymeric structure. The input data must be generated from an extensive series of experimental measurements for each coal of interest. Very significant computational expense and application restricted to coals, which have already been studied, are implied. All of these problems are exacerbated when coal blending or co-firing with renewable solid fuels, such as forest and agricultural waste, and sewage sludge, is considered. In this paper, a new approach based on neural networks is proposed; it is capable of handling a range of solid fuels. The model considers heating rate, fuel atomic ratios, and the temperature of the fuel particles to predict the volatiles released by the particles. The 'learning' properties of the model implicitly facilitate all the physical conditions of devolatilization experiments, which were used during its training and validation phases. The neural-network model was implemented into an existing 3D CFD combustion code. The predictions for high- and low-NOx burners demonstrate improved prediction of in-flame data for reduced computational effort, one-fifth of that with the standard single-global-reaction devolatilization model. Its devolatilization predictions have also been compared with a detailed devolatilization model (FLASHCHAIN) and were found to be comparable. 04/01592 An evaluation of the self-determined probability- weighted moment method for estimating extreme wind speeds Whalen, T. M. et al. Journal of Wind Engineering and Industrial Aerodynamics, 2004, 92, (3-4), 219 239. For the estimation of probability distribution parameters, the method "o f self-determined probability-weighted moments (SD-PWM) has previously been introduced as a refinement on the original method of probability-weighted moments (PWM). Tables have been created summarizing the solution of the relevant equations for certain probability distributions, but application of these is awkward. In addition, certain associated algorithms are difficult to interpret and contain formulations that do not appear to properly enforce the definitions of self-determined probability-weighted moments. There- fore, new algorithms have been developed to both clarify and simplify the determination of SD-PWM parameter estimates. As an application of the SD-PWM algorithms, the estimation of extreme wind speeds is considered using the Gumbel and generalized extreme value (GEV) distributions. The estimation results are compared to similar results obtained via PWM, the method of moments and the maximum likelihood method. The analyses suggest SD-PWM may be a reasonable tool for analysing the ability of a particular distribution to describe a sample. Relative to the method of moments and PWM estimates, the SD-PWM estimates compare well based on fits of the cumulative distributions, While the SD-PWM estimates exhibit increased variability relative to the method of moment (MOM) estimates, SD-PWM wind speed estimates are generally conservative relative to the MOM estimates. 04/01593 Analytic derivation of the correction factor for the improved coarse mesh method Yamamoto, A. Annals of Nuclear Energy, 2004, 31, (1), 71-86. A correction factor for the improved coarse mesh (ICM) method was analytically derived based on an explicit solution of a diffusion equation in one-dimensional geometry. In the conventional approach, the correction factors of the ICM method were derived by a neutron balance equation on virtual mesh points in an actual mesh. However, in the analytical approach, the correction factors were derived using a rigorous form of a finite-difference formulation of diffusion equation in one-dimensional geometry. Test calculations in one-dimensional slab and two-dimensional PWR colour-set geometries showed that the spatial discretization error can be further reduced by utilizing the analytically derived correction factors instead of the original ones. The newly derived correction factors for the ICM method can be easily implemented in the existing code since only expression of the correction factor is modified. Furthermore, since the ICM can be applied to existing finite-difference diffusion code with minor modifications and slight additional computation time, it is useful for scoping purpose which requires fairly accurate results within a short computation time, e.g. in-core fuel management calculations. 04/01594 Application of quantum chemistry calculation to investigation of coal reactivity Wang, B. et al. Meitan Zhuanhua, 2003, 26, (1), 1-7. (In Chinese) The methods of quantum chemical calculation generally used in the investigation on reactivity of coal are introduced in this paper. The applications of quantum chemical calculation to the two kinds of important coal reactivities are summarized, first is the change of chemical bonds and thermodynamic parameters and the reaction kinetics during pyrolysis of coal, and the second is the reaction mechanism and kinetics of coal surface structure under the action of carbon dioxide and methane. Through studies on relative work now available, the characteristics and function of quantum chemical calculation in the investigation for coal reactivity are discussed. The key problem of the application of quantum chemical calculation to the coal reactivity is how to establish reasonably and select an initial model which can represent the characteristics of the research processes are considered. 04/01595 BWR fuel reloads design using a Tabu search technique Castillo, A. et al. Annals of Nuelear Energy, 2004, 31, (2), 151-161. A system has been developed to design optimized boiling water reactor fuel reloads. This system is based on the Tabu Search technique along with the heuristic rules of Control Cell Core and Low Leakage. These heuristic rules are a common practice in fuel management to maximize fuel assembly utilization and minimize core vessel damage, respect- ively. The system uses the 3-D simulator code CM-PRESTO and it has as objective function to maximize the cycle length while satisfying the operational thermal limits and cold shutdown constraints. In the system tabu search ideas such as random dynamic tabu tenure, and frequency- based memory are used. To test this system an optimized boiling water reactor cycle was designed and compared against an actual operating 216 Fuel and Energy Abstracts May 2004 16 Fuel science and technology (fundamental science, analysis, instrumentation) cycle. Numerical experiments show an improved energy cycle com- pared with the loading patterns generated by engineer expertise and genetic algorithms. 04/01596 CELLO: an advanced LBIC measurement technique for solar cell local characterization Carstensen, J. et al. Solar Energy Materials and Solar Cells, 2003, 76, (4), 599-611. An advanced light beam-induced current measurement for solar cell local characterization, called CELLO, has been developed and tested on mono- and multi-crystalline Si solar cells. A solar cell is illuminated at near 1.5 AM light intensity, and is additionally subjected to intensity modulated scanning local illumination by a focused IR-laser. The linear response (current or potential) of the solar cell is measured for various fixed global conditions (different preset voltage or current values) during scanning. A large number of independent data with high spatial resolution are obtained. Applying an advanced fitting procedure to these data yields a set of local parameters for each point on the solar cell. This gives information on the spatial distribution of the photo current, the series and shunt resistance, the lateral diffusion of minority carriers, the quality of the back surface field, and even allows the calculation of local IV curves. The theoretical and experimental approach to this technique will be discussed, and the applicability of this new solar cell characterization tool will be demonstrated. 04/01597 Change in viscosity of softening coal upon heating with its liquid content. Part h linear relationship between logarithm of viscosity and liquid fraction Hayashi, J.-I. et al. Fuel, 2003, 82, (t4), 1735-1741. A variable-force-loading needle penetrometry and a proton magnetic resonance analysis were performed for in situ measurements of shear- rate-independent viscosity of softening coal pellet upon heating, 7, and the fraction of mobile hydrogen existing in the liquid phase, 0~h, respectively. During isothermal heating of the pellet at temperature in a range from 680 to 730 K, ~mh changed with time via a maximum while ~7 did inversely. At every temperature examined, the time for the maximum ~mh coincided with that for the minimum 71. This result qualitatively validated the experimental definition of the liquid fraction in the softening coal as a liquid/solid suspension by ~br~h- Further analysis of the results revealed that the logarithm of ~7, which changes in a rang e from 10 l to 104 Pa s upon isothermal heating, is correlated linearly with the liquid fraction ranging from 0.1 to 0.5. For each of the pellets made of two different coals, it was found that the logarithm and ~mh varied being governed by a single linear relationship upon both isothermal heating and non-isothermal heating. Such a single relationship, which was valid over a temperature range from 600 to 800 K, suggested fairly small temperature dependency of the viscosity of liquid in the softening coal. Large spills of refined petroleum products have been an occasional occurrence over the past few decades. This has not been true for large spills of liquefied natural gas (LNG). This paper compares the likely similarities and differences between accidental releases from a ship of sizable quantities of these different hydrocarbon fuels, their sub- sequent spreading, and possible pool-fire behaviour. Quantitative estimates are made of the spread rate and maximum slick size, burn rate, and duration; effective thermal radiation; and subsequent soot generation. 04/01600 Complex permittivities and dielectric relaxation of granular activated carbons at microwave frequencies between 0,2 and 26 GHz Atwater, J. E. et al. Carbon, 2003, 41, (9), 1801 1807. Carbonaceous materials are amenable to microwave heating to varying degrees. The primary indicator of susceptibility is the complex permittivity (e*), of which the real component correlates with polarization and the imaginary term represents dielectric loss. For a given material, the complex permittivity is dependent upon both frequency and temperature. Here the complex permittivities of three activated carbons of diverse origin over the frequency range from 0.2 to 26 GHz were reported. Dielectric polarization-relaxation phenomena for these materials are also characterized. Measurements were made using a coaxial dielectric probe and vector network analyser based system across the temperature region between 22 and 190C. 04/01601 Computational study of opposed-force-flow flame spread across propanol pools Kim, I. and Sirignano, W. A. Combustion and Flame, 2003, 132, (4), 611-627. Two-dimensional flame-spread across sub-flash-point propanol pools in opposed-forced airflow is investigated numerically for normal and zero gravities with finite-rate, one-step chemical kinetics, variable properties, and an adaptive finite-difference gridding scheme. Effects of air speed, liquid depth, and gravity on the characteristics of the flame-spread are examined with correct initial profiles for the gas- phase velocity and the mass-fraction of fuel vapor before ignition. Some of the results are as follows: (1) 10-ram pools are deep enough to examine flame-spread rates on deep pools in the uniform regime and pulsation frequencies on deep pools in the pulsating regime; (2) the pseudo-uniform regime is found only in deep pools and not in shallow pools; (3) the effect of opposed-forced airflow on the flame-spread rate is different, depending on the regime for To, where To denotes the initial pool temperature. Effects of pool depth on the liquid phase are also investigated: there is only a surface-tension-driven flow in the liquid phase of shallow pools. Finally, the flame-spread regime is displayed as a function of initial pool temperature, air speed, pool depth, and gravity. 0401598 Change in viscosity of softening coal upon heating with its liquid content, Part II, Examination of rheological property and phase structure of softening coal Hayashi, J.-I. et al. Fuel, 2003, 82, (14), 1743-1750. The phase structure of softening coal upon heating is discussed based on the relationship between the shear-rate-independent viscosity (r/) and the fraction of liquid (41) reported in the first part of this series paper, as well as results of previous studies on rheologieal property and physical structure of softening coal. Firstly, the existing models that assume softening coal to be a suspension of 'rigid' solid particles are examined focusing on their applicability to description of the observed of 1og(~7)-61 relationship. The examination reveals that none of the models can describe the particular features the log(~/)-~a relationship: linearity and insignificant sensitivity to temperature Apparent success of the existing models is attributed to problems such as no or inappropriate experimental definition of the liquid fraction as well as unsuitable estimation or measurement of the viscosity. Secondly, it is demonstrated that the linear logQ/)-~l relationship is explained best by considering that the softening coal is a suspension of 'deformable' solid. Thirdly, further examination of the new suspension model draws the following characteristics of the phase structure of the softening coal. The so-called plastic domain in the softening coal consists of the liquid phase, optically isotropic solid phase and anisotropic mesophase- like spherules. The isotropic solid phase and the anisotropic phase, both of which are detected as the solid by 1H-NMR, would have very similar viscosities so that their influences on the viscosity of the plastic domain are undistinguishable. The plastic domain is suspended with coarse grains of minerals and inert organics, while they are not responsible for the change in the viscosity of the whole softening coal upon heating. The viscosity is mainly a function of the solid/liquid fractions in the plastic domain. 04101599 Comparison of hypothetical LNG and fuel oil fires on water Lehr, W, and Simecek-Beatty, D. Journal of Hazardous Materials, 2004, 107, (1-2), 3-9. 04/01602 Detailed modeling of hybrid reburn/SNCR processes for NOx reduction in coal-fired furnaces Hart, X. et al. Combustion and Flame, 2003, 132, (3), 37~386. Mechanism reduction has made the detailed kinetic modelling of combustion problems much easier; it also offers potential improvement of modelling accuracy and flexibility in comparison to global mechanisms. The present work applies mechanism reduction in conjunction with the CHEMKIN library and develops an automatic reduction programme code. Regarding the hybrid re-burn/selective non-catalytic reduction (SNCR) ('advanced re-burning') conditions in coal-fired furnaces and based on a full mechanism 'GADM98', a skeletal mechanism with 39 species, 105 reactions, and further a 10- step/14-species reduced mechanism were established. The reduced mechanism was implemented into a 3D-combustion computational fluid dynamics (CFD) code. The eddy-dissipation-concept model was used to describe the influence of turbulence on the combustion chemistry. A large number of simulations for reburning and hybrid reburn/SNCR processes in a coal-fired reactor were executed; the predicted results were compared with experimental measurements. The reduced mechanism and the comprehensive modelling give quite satisfactory results over a wide range of mole ratios for /3 = [NH3]/ [NO] and air/fuel equivalence ratios Az in the reburn zone. From the modelling results, it was found that adding ammonia premixed with reburn fuel (CH4) effects no further reduction of NO or even impairs the reduction efficiency compared to pure reburning, and in contrast, staged addition of ammonia downstream of the CH4 injection in the reburn zone provokes a significant further reduction of NOx over a wide range of parameters. According to the predictions, NOx-reduetion rates of 50-60% and of 70-80% can be achieved through pure reburning and hybrid reburn/SNCR approaches, respectively, at A2 = 0.95 and /3 = 1.5. Concerning the computational procedure, essential measures were taken to optimize convergence and computing time. The computing time with the present reduced mechanism is N2.5 times that with the traditional global mechanism for the same iteration number. Tabulation of the rate constants reduced the computing time of the reaction kinetics by ~50%. Fuel and Energy Abstracts May 2004 217


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