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.

04•01590 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 o f 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