04/01275 Porous structure evolution of cellulose carbon fibres during heating in the initial activation stage Babel, K. Fuel Processing Technology, 2004, 85, (1), 75 89. This paper is focused on the description of changes in the porous structure during fast heating to the activation temperature of the viscose fibres, pyrolysed to different final temperatures. Standard regenerated cellulose fibre structures were tested. Fabrics were subjected to pyrolysis, the samples being heated to final temperatures of 400, 600 and 850°C. Carbon fibres were subsequently heated to activation temperature (850°C) at a rate of 100°C/rain, and then the samples were cooled down. The characteristics of obtained carbon preparations were examined. A level of restructuring and internal ordering of fibres was defined which originated during slow pyrolysis as well as the range of temperature differences of pyrolysis and activation where fast increase of carbon fibre temperature before activation is advantageous for the development of porous structure. It allows for partial release of pores and fast rebuilding of structure accompanied by a considerable number of defects in the carbon matrix with higher reactivity to oxidizer, which, in turn, promotes the development of pores in active carbon during oxidation. Temperature difference for viscose carbon fibres is approximately 150-300°C at pyrolysis tempera- ture of 550-700°C.

04/01276 Preparation and pore control of highly mesoporous carbon from defluorinated PTFE Tanaike, O e t al Carbon, 2003, 41, (9). 1759 1764. Porous carbon having more than 2000" m2/g of BET specific surface area was synthesized by defiuorination of polytetrafluoroethylene (PTFE) at 473 K using sodium metal. The porous carbon as-prepared had a large amount of narrow mesopores 2-3 nm in pore width, together with micropores. Control of the pore structure was attempted by simple heat-treatment of the carbon in nitrogen, and change of the porous structures was characterized by nitrogen adsorption techniques. As a result, it was found that the ratio between micro- and mesopores was easily varied. Electric double layer capacitance was measured as one of the applications for the mesoporous carbon with specific porosity, and the effect of pore control on capacitance was investigated.

04101277 Production of carbon molecular sieves by plasma treated activated carbon fibers Orfanoudaki, T. et al. Fuel, 2003, 82, (15-17), 2045 2049. Carbon molecular sieves (CMS) are valuable materials for the separation and purification of gas mixtures. In this work, plasma deposition was used aiming to the formation of pore constrictions, by narrowing the surface pore system of commercial activated carbon fibres (ACF). For this reason propylene/nitrogen or ethylene/nitrogen discharges of 80 and 120 W were used. The molecular sieving properties of the plasma treated ACF were evaluated by measuring the adsorption of CO2 and CH4. The CO2/CH4 selectivity was significantly improved and depended on plasma treatment conditions (discharge gas and power). The optimum C02/CH4 selectivity (26) was observed for C2H4/N2 plasma treated ACF at 80 W. Sample scanning electron microscopy (SEM) analysis after plasma treatment revealed an external film formation and X-ray photoelectron spectroscopy (XPS) analysis showed the incorporation of nitrogen functional groups in the film, which probably interact with CO2, thereby altering CO2/CH2 selectivity.

04•01278 Strength of neutron-irradiated high-quality 3D carbon fiber composite Snead, L. L. et al. Journal o f Nuclear Materials, 2003, 321, (2-3), 165- 169. The effects of neutron irradiation to 10 dpa at 500 and 800°C on a high-quality three-dimensional balanced weave composite (FMI-222) is presented. Strength and dimensional stability for this system is compared to earlier work on this material, at lower dose, and contrasted with that of a well studied isotropic graphite (POCO AXF-5Q) irradiated at identical conditions. For both irradiation temperatures the composite strength in bending is substantially increased. While both irradiation temperatures cause contraction along the bend bar axis, the amount of contraction is greater for the higher temperature irradiation. Moreover, for the 500°C irradiation the corresponding decrease in volume is observed, though an apparent large increase in volume occurs for the 800°C irradiated composite. This departure from isotropic dimensional change is explained in terms of fibre dimensional stability model previously presented.

05

05 Nuclear fuels (scientific, technical)

NUCLEAR FUELS

Scientific, technical

04•01279 Analyses of static energy conversion systems for small nuclear power plants El-Genk, M. S. and Tournier, J.-M. P. Progress in Nuclear Energy, 2003, 42, (3), 283-310. Small, Gas Cooled Reactor (GCR) nuclear power plants with static energy conversion could meet the energy mix in underdeveloped countries, including electricity, residential and industrial space heating, seawater desalination, and/or high temperature process heat or steam for industrial uses. Analyses are performed of one high-temperature GCR and three intermediate-temperature GCR power plants with co- generation options to calculate and compare the total energy utilizations of the plants. Conversion of the reactor thermal power to electricity is accomplished using static energy conversion units comprised of an Alkali Metal Thermal-To-Electric topping cycle and a Thermoelectric bottom cycle, as well as segmented thermoelectric converters. The calculated total energy utilization of these plants of 95% includes low-voltage (~400 V) DC electrical power at a net plant efficiency of up to 32,7%, and co-generation for residential and industrial space heating at <400 K, desalination at 365 K, and/or high temperature process heat or steam at >500 K. Results indicate that the intermediate-temperature GCR plants with a small coolant tempera- ture rise of 100-160 K in the reactor core could deliver 2-3 times the electricity of a GCR plant with a higher temperature rise of 340 K, and that all plants could provide for both seawater desalination and high temperature process heat/steam concurrently. In addition, depending on the number of co-generation options employed, the fraction of the reactor thermal power used for co-generation in the high-temperature GCR plant is ~10-30% higher than in the intermediate-temperature GCR plants with a smaller temperature rise in the reactor.

04•01280 Artificial neural networks for dynamic monitoring of simulated-operating parameters of high temperature gas cooled engineering test reactor (HTTR) Eker, S. et al. Annals of Nuclear Energy, 2003, 30, (17), 1777-1791. This paper addresses the problem of utilization of the artificial neural networks (ANNs) for detecting anomalies as well as physical parameters of a nuclear power plant during power operation in real time. Three different types of neural network algorithms were used namely, feed-forward neural network (back-propagation, BP) and two types of recurrent neural networks (RNN). The data used in this paper were gathered from the simulation of the power operation of the Japan's High Temperature Engineering Testing Reactor (HTTR). For the wide range of power operation, 56 signals were generated by the reactor dynamic simulation code for several hours of normal power operation at different power ramps between 30 and 100% nominal power. Paper will compare the outcomes of different neural networks and presents the neural network system and the determination of physical parameters from the simulated operating data.

04/01281 Behaviour of fission gases in an irradiated nuclear fuel under ~ external irradiation Desgranges, L. et al. Journal of Nuclear Materials, 2003, 321, (2-3), 324 330. The a-self-irradiation could influence the behaviour of nuclear spent fuel in storage conditions. To evaluate some of these effects, a UO2 fuel, irradiated in a PWR, was irradiated with a helium beam at different doses. PIXE measurements of xenon and neodymium concentration on helium irradiated and non-irradiated areas showed that no major difference in the distribution of these fission products occurred due to helium irradiation. From these results, it is concluded that helium irradiation associated with a self-irradiation does not induce significant modification of gaseous fission products in storage conditions.

04/01282 Cross-section measurements for the 97Mo (n,p) ~TmNb reaction at the neutron energies from 13.6 to 14,9 MeV Bostan, M. et al. Annals of Nuclear Energy, 2003, 30, (17), 1821-1828. Cross-sections were measured at neutron energies from 13.6 to 14.9 MeV for the reaction 97mMo(n,p) 97mNb leading to isomer of Niobium- 97 isotope. The production of relatively short-lived isomer activity and the spectra accumulation have been carried out by cyclic activation method. Corrections were made for the effects of gamma ray attenuation, random coincidence summing (pulse pileup), dead time, neutron flux fluctuations and scattered low energy neutron contri- bution. Statistical model calculations for which the pre-equilibrium

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