16 Fuel science and technology (fundamental science, analysis, instrumentation)

are two main reasons for using flexible HGITL. They are: (1) to overcome the technical problems and the huge cost associated with the on-site welding of large number of coaxial cylinders; and (2) to improve the utilization of the internal insulation system. The results are interpreted in terms of the basic principles of the streamer criterion in compressed gases, and also their trends are compared with those for other experimental works. The results reveal that HGITL have superior mitigation of the particle-initiated corona activities over the normal GITL, where the bundled HGITL have less improvement. The corona inception voltage decreases with the increase in the wire length, the surface charge density on the conductor insulation/spacers and the close proximity to charged or uncharged spacers, and with the decrease in pressure. On contrary, the number of occurrence of streamers and the integration of the effective ionization coefficient have opposite trends. Ribbed spacers are less sensitive to particle length and show a considerable improvement in the insulation reliability, especially when the rib becomes closer to the conductor insulation.

04/01653 Theoretical and experimental investigations of reactor parameters in a U-233 fuelled research reactor Mohapatra, D. K. et al. Annals o f Nuclear Energy, 2004, 31, (2), 197- 212. The Kalpakkam Mini Reactor (KAMINI) has the unique distinction of being the only operating pool type research reactor in the world at present, that utilizes U-233 as the fissile material. It is a 30 kW pool type reactor, operated with an alloy of U-233 and aluminium as fuel, light water as moderator and beryllium oxide as reflector. It is designed to operate at a maximum power level of 30 kW and mostly used for neutron radiography and neutron irradiation experiments. In the present work core calculations are carried out to estimate the worth of safety control plates (SCPs) and one adjustable reflector block of KAMINI by using the lattice homogenization code SMAXY and 3-D transport code TRITAC along with the WIMS cross-section data library. The worth of the SCPs is determined experimentally by rod drop method. A comparison of the calculated worth values, is done with the experimentally determined ones. The neutron spectra measurements carried out at two-sample irradiation locations, called thimble irradiation locations in KAMINI are also presented in this work. The neutron spectra at the thimble irradiation locations are generated by, the help of core calculations performed by SMAXY, TRITAC and WIMS combination. The measured total fluxes, fluxes in various neutron energy ranges and the gold reaction rates at both the thimble locations are compared with the calculated values. It is found that the calculated values of worths and fluxes match well with the measured values.

04/01654 Theoretical derivation of the interaction effects with expansion effects to bubbly two-phase flows Espinosa-Paredes, G. et al. Annals of Nuclear Energy, 2004, 31, (2), 117-133. This paper was concerned with a theoretical closure relationships derivation to describe the hydrodynamic interaction in a dilute dispersion of gas bubbles in a continuous liquid phase with bubble radius variation due to expansion effects. The starting point in the present study was the three-dimensional transient averaged transport equations. The closure relationships were formulated as an associated problem for the deviation around averaging values of the local variables. The derivations were based on the concentric cell approach and taking in account compressibility of the gas phase. The closure relationships for the dyad product of velocity spatial deviations, virtual mass and the difference between the intrinsic and interface averages of the pressure on the continuous phase side were developed. In this work a new term, which is a function of the squared radial velocity, into the closure for the dyad product of velocity spatial deviation was founded.

04•01655 Thermodynamics of gas-char reactions: first and second law analysis Prins, M. J. et al. Chemical Engineering Science, 2003, 58, (3-6), 1003- 1011, In energy transformation processes such as combustion, gasification and reforming of fossil and renewable fuels, the conservation of energy (first law of thermodynamics) as well as the quality of energy (second law of thermodynamics) is important. This study focuses on the conversion of biomass with air and/or steam into gaseous components and char represented by solid carbon (graphite). Energy and exergy (available energy) losses are analysed by calculating the composition of a dry, ash-free typical biomass feed represented by CH1.400.59N0.0017 in equilibrium with varying amounts of air and/or steam. The analysis is carried out for adiabatic systems at atmospheric pressure, with input of biomass and air at ambient conditions and steam at atmospheric pressure and temperature of 500 K. For air gasification, energy and exergy in the product gas have a sharp maximum at the point where all carbon is consumed, the carbon boundary point. This is the optimum point for operating an air-blown biomass gasifier. For gasification with steam, operation at the carbon boundary point is also optimal, but

thermodynamic process losses hardly increase when adding more steam than required. The efficiency of steam and air-blown gasification was compared using the definition of rational efficiency. Although gasification by steam is more efficient (87.6% vs. 80.5%), this difference i s expected to level off if exergy losses for the production of steam are taken into account. The choice between steam and air as a gasifying medium therefore seems to depend more on the required gas compositions. For steam gasification, the product gas contains mainly methane and carbon dioxide, while hydrogen, carbon monoxide, and (at least 38% nitrogen are the main product gases for air gasification.

04/01656 Three-dimensional simulation of threshold porosity for fission gas release in the rim region of LWR UO2 fuel Koo, Y.-H. et al. Journal of Nuclear Materials, 2003, 321, (2-3), 249- 255. The threshold porosity above which fission gas release channels would be formed extensively in the rim region of high burnup UO2 fuel was estimated by the Monte Carlo method and Hoshen-Kopelman

.algorithm. With the assumption that both rim pore and rim grain can be represented by cubes, the pore distribution in the rim was simulated three-dimensionally by the Monte Carlo method according to rim porosity and pore size distribution. Using the Hoshen-Kopelman algorithm, the fraction of open rim pores interlinked to the outer surface of a fuel pellet was derived as a function of the rim porosity. The simulation revealed that it is the rim porosity rather than the pore size distribution or rim thickness that determines the fraction of open pores connected to the pellet surface. The analysis also indicated that the threshold porosity is around 24%, above which the number of rim pores forming release channels increases very rapidly. 2 fuel

04/01657 Trajectories of spheres in strong winds with application to wind-borne debris Holmes, J. D. et al. Journal of Wind Engineering and Industrial Aerodynamics, 2004, 92, (1), 9-22. In this paper, trajectories of spheres, carried by strong winds, are studied theoretically and numerically. The application is to wind-borne debris occurring in severe windstorms such as hurricanes. It is shown that the effect of vertical air resistance is significant, and should be included to accurately predict both horizontal and vertical velocities and displacements. Turbulence appears to have little effect on average trajectories, but produces significant variability in individual trajectories.

04/01658 Utilizing Preisach models of hysteresis in the computation of three-phase transformer inrush currents Adly, A. A. et al. Electric Power Systems Research, 2003, 65, (3), 233- 238. A new approach through which transformer magnetizing inrush currents associated with the energization of three-phase transformers may be computed while accurately taking the effect of hysteresis into consideration. Transformer operating conditions such as switching-on angle and residual flux are also included. The simulation results are compared with those obtained experimentally in a laboratory model transformer.

04/01659 Validation of atmospheric dispersion models using ETEX data Sandu, I. et al. International Journal of Environment and Pollution, 2003, 19, (4), 367-389. Two models frequently used to simulate the dispersion of pollutants in the atmosphere have been compared. This is necessary because only a well-tested and well-calibrated simulation model can be a good representation of the reality of the dispersion of pollutants. The models evaluated (HYSPLIT_4 with its four variants and MEDIA) were run using as input parameters the same meteorological dataset (for 23-26 October 1994) from the French model ARPEGE. The following statistical criteria were compared: the space and time evolution of the pollutant cloud; the variation of statistical parameters in time and space; and the differences between the simulated and measured values of concentration in time for six different stations. The results emphasize the characteristics of the two models and their abilities in the framework of the air quality monitoring.

04/01660 Wood-ethanol for climate change mitigation in Canada Graham, P. J. et al. Applied Biochemistry and Biotechnology, 2003, 105- 108, 231-242. The impetus for this paper is Canada's commitment under the United Nations Framework Convention on Climate Change to reduce national greenhouse gas emissions as well as reducing the dependency on fossil fuels. Wood-based ethanol offers and excellent opportunity for greenhouse gas mitigation due to market potential, an ability to offset significant emissions from the transportation sector, a reduction of emissions from CO2-intensive waste-management systems, and carbon

224 Fuel and Energy Abstracts May 2004