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

their expected abundance in tissue samples. Animal tissue samples showed variable PCB patterns and abundances although all animals were expected to have been exposed to Aroclor :~) 1260. These characteristics are thought to be related to the structure of the food web or metabolic and physiological features of the individual animals. Grass carp samples had excellent correlation in the isotopic compo- sitions of the congeners. Although the correspondence of 613C in congeners from fresh Aroclor 1260 to congeners from tissue samples may not be expected to be identical, the patterns of similarity were very supportive of the maintenance of the isotopic signal into the food chain. The patterns observed in these and other samples suggest a fraetionation process where residual congener pools can become progressively enriched while the congeners produced from degradation are more depleted. The isotopic patterns provide insight to degradation processes and into relative metabolic stability of the various congeners in different animals. The results of this study suggest that CSIA analysis of PCBs at natural abundance can provide significant insight into tracing these compounds through the natural environment. The data also suggest that tracking PCB mixtures may be possible using CSIA techniques after standard chromatographic matching or other fingerprinting techniques become blurred.

04•01647 Stability analysis of rotor-bearing systems via Routh-Hurwitz criterion E1-Marhomy, A. A. and Abdel-Sattar, N. E. Applied Energy, 2004, 77, (3), 287-308. A method of analysis is developed for studying the whirl stability of rotor-bearing systems without the need to solve the governing differential-equations of motion of such systems. A mathematical model, comprised of an axially symmetric appendage at the mid-span of a spinning shaft mounted on two dissimilar eight-coefficient bearings, is used to illustrate the method. Sufficient conditions for asymptotic stability of both the translational and rotational modes of motion of the system have been derived. The system's stability boundaries, presented graphically in terms of the various system non-dimensionalized parameters, afford a comprehensive demonstration of the effects of such parameters on the system's stability of motion.

04/01648 Stimulation experiments in sedimentary, Iow- enthalpy reservoirs for geothermal power generation, Germany Legarth, B. et al. Geothermics, 2003, 32, (4-6), 487-495. Hydraulic stimulation experiments were conducted in a re-used Rotliegend well situated in the eastern part of the North German Basin. The well is used as an 'in-situ geothermal laboratory' and as a reference location for several ongoing research projects. The aim of the projects and experiments is to develop technologies that will put primary low-productive aquifer structures into use for geothermal power generation. The frac operations in 2002 were designed to enhance the inflow performance by connecting the well to productive reservoir zones. Two consecutive zones within the Rotliegend sandstones were selected. Here core measurements show the most promising petrophysical reservoir properties with respect to a productivity increase. The stimulation treatments were performed as hydraulic proppant fracturing operations. Proppants were used to support the fractures and to guarantee a long-term fracture aperture. The treatment intervals are located in the open-hole section of the well at depths between 4080 m and 4190 m and at temperatures of about 140°C. The technical demands were therefore unprecedented in these challenging conditions. An open-hole-packer at the top and a sand plug at the bottom of each interval were used as hydraulic barriers. Applying this configuration the intervals were fracture-treated by injecting about 11 tonnes of proppant (high-strength ceramic grains) and over 200 m 3 of frae fluid (highly viscous gel) into the formation. The fracture treatments were conducted by means of two successive operations in each interval: first, a diagnostic treatment (datafrac), followed by the main treatment (mainfrac) with the proppant stages. The frac operations were successful. Propped fractures were created in both intervals and the inflow behaviour of the reservoir was decisively enhanced. The effective pressures applied for fracture initiation and propagation were only slightly above the in-situ pore pressures. The stimulation ratio predicted by modelling, however, could not be achieved. There were a number of reasons for this mismatch. Probably chemical and mechanical processes during closure led to a reduced fracture conductivity. The insights gained from the experiments are important for future fracture treatment projects on this site and in comparable locations.

ment, infrared spectroscopy, potentiometric titration, copper adsorp- tion from solution and physical adsorption of N2 at -196°C and CO2 at 0°C. It was shown that, similarly to synthetic phosphoric acid activated carbons obtained in argon, the synthetic carbons activated with phosphoric acid in air possess an acidic character and show considerable cation-exchange properties. The contribution of oxygen- containing surface groups along with phosphorus-containing groups to CEC is higher for carbons obtained in air. Three types of surface groups were identified on carbons prepared at temperatures up to 600°C, and four types on carbons prepared at higher temperatures. These groups were assigned to 'super-acidic' (pK<0), phosphorus- containing (pK=l .1 1.2), carboxylic (pK=4.7-6.0) and phenolic (pK=8.1-9.4) groups. The cation-exchange capacity was at a maxi- mum for the carbon prepared at 800°C. Copper adsorption by synthetic phosphoric acid activated carbons obtained in air at temperatures lower than 800°C is higher than for similar carbons obtained in argon. The increase is due to additional formation of oxygen-containing surface groups. Calculated copper binding constants revealed the importance of phosphorus-containing and carboxylic groups for adsorption of copper from aqueous solution. All carbons show a multimodal pore size distribution including simultaneously micropores and mesopores, but the porous texture is not a prime factor in determining the cation-exchange capacities of these carbons. Synthetic phosphoric acid activated carbons show a greater development of porosity when obtained in air as compared to carbons carbonized in argon.

04•01650 The burnup capabilities of the deep burn modular helium reactor analyzed by the Monte Carlo continuous energy code MCB Talamo, A. et al. Annals of Nuclear Enecgy, 2004, 31, (2), 173 196. The waste actinide burnup capabilities of a Gas Turbine Modular Helium Reactor (GT-MHR, similar to the reactor being designed by General Atomics and Minatom for surplus weapons plutonium destruction) have been investigated with the Monte Carlo Continuous Energy Burnup Code MCB, an extension of MCNP developed at the Royal Institute of Technology in Stockholm and University of Mining and Metallurgy in Krakow. The GT-MHR is a gas-cooled, graphite- moderated reactor, which can be powered with a wide variety of fuels, like thorium, uranium or plutonium. In the present work, the GT- MHR is fueled with the transuranic actinides contained in Light Water Reactors (LWRs) spent fuel for the purpose of destroying them as completely as possible with minimum reliance on multiple reprocessing steps. After uranium extraction from the LWR spent fuel (UREX), the remaining waste actinides, including plutonium are partitioned into two distinct types of fuel for use in the GT-MHR: Driver Fuel (DF) and Transmutation Fuel (TF). The DF supplies the neutrons to maintain the fission chain reaction, whereas the TF emphasizes neutron capture to induce a deep burn transmutation and provide reactivity control by a negative feedback. When used in this mode, the GT-MHR is called Deep Burn Modular Helium Reactor (DB-MHR). Both fuels are contained in a structure of triple isotropic coated layers, TRISO coating, which has been proven to retain fission products up to 1600°C and is expected to remain intact for hundreds of thousands of years after irradiation. Other benefits of this reactor consist of: a well- developed technology, both for the graphite-moderated core and the TRISO structure, a high energy conversion efficiency (about 50%), well established passive safety mechanism and a competitive cost. The destruction of more than 94% of 239Pu and the other geologically problematic actinide species makes this reactor a valid proposal for the reduction of nuclear waste and the prevention of proliferation.

04/01651 The fuzzy clearing approach for a niching genetic algorithm applied to a nuclear reactor core design optimization problem Sacco, W. F. et al. Annals of Nuclear Energy, 2004, 31, (1), 55 69. This article extends previous efforts on genetic algorithms (GAs) applied to a core design optimization problem. This study introduced the application of a new Niching Genetic Algorithm (NGA) to this problem and compared its performance to these previous works. The optimization problem consisted of adjusting several reactor cell parameters, such as dimensions, enrichment and materials, in order to minimize the average peak-factor in a three-enrichment zone reactor, considering restrictions on the average thermal flux, criticality and sub-moderation. After exhaustive experiments it was observed that the new niching method performs better than the conventional GA due to a greater exploration of the search space.

04•01649 Synthetic carbons activated with phosphoric acid III. Carbons prepared in air Puziy, A. M. et at. Carbon, 2003, 41, (6), 1181-1191. Synthetic activated carbons were prepared by phosphoric acid activation of a styrene-divinylbenzene copolymer in an air atmosphere at various temperatures in the 400-900°C interval. The carbons were characterized by elemental analysis, cation-exchange capacity measure-

04/01652 Theoretical analysis of particle-initiated corona activities in hybrid gas-insulated transmission lines Metwally, I. A. Electric Power Systems Research, 2003, 66, (2), 123- 131. This paper theoretically addresses the factors affecting the partial discharge activities due to metallic particles in hybrid gas-insulated transmission lines (HGITL) using the charge simulation method. There

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