- Email: [email protected]
01612 A heterogeneous coarse mesh solution for the 2-D NEA C5G7 MOX benchmark problem
05 Nuclear fuels (scientific, technical) content. Mechanical. electrical and thermal properties of low viscosity epoxy composites were resulted better than that of the high viscosity composites.
06•01607 Mechanical and structural characterization of electrospun PAN-derived carbon nanofibers Zussman, E. et al. Carbon, 2005, 43, (10), 2175 2185. The mechanical and structural properties of individual electrospun PAN-derived carbon nanofibres are presented. EELS spectra of the carbonized nanofibres shows the C atoms to be partitioned into approximately 80% sp 2 bonds and approximately 20% sp 3 bonds, which agrees with the observed structural disorder in the fibres. TEM images show a skin-core structure for the fibre cross-section. The skin region contains layered planes oriented predominantly parallel to the surface, but there are some crystallites in the skin region misoriented with respect to the fibre long axis. Microcombustion analysis showed 89.5% carbon, 3.9% nitrogen, 3.08% oxygen and 0.33% hydrogen. Mechanical testing was performed on individual carbonized nanofibres a few microns in length and hundreds of nanometers in diameter. The bending modulus was measured by a mechanical resonance method and the average modulus was 63 GPa. The measured fracture strengths were analysed using a Weibull statistical distribution. The Weibull fracture stress fit to this statistical distribution was 0,64 GPa with a failure probability of 63%.
06•01608 Modeling of fishbone-type carbon nanofibers: a theoretical study Zhu, Y. A. et al. Carbon, 2005, 43, (8), 1694-1699. Five models for fishbone-type carbon nanofibres (f-CNFs) have been proposed and their geometries have been optimized through molecular dynamics and molecular mechanics simulations. The angle between graphene layers and fiber axis can take the values 9.71 °, 19.60 °, 30.03 °, 41.99 ° , and 56.43 ° , which agree satisfactorily with the experimentally determined values. With reduction of the angle, the interlayer spacing of graphene sheets increases fi'om 0.3376 nm to 0.3392 nm accordingly, due to the strain of the graphitic cones. In addition, X-ray diffraction (XRD) simulations are also implemented. With the high-resolution transmission electron microscopy (HRTEM) results taken into account, the X R D simulations verify that f-CNFs can adopt not only a regular arrangement but also a turbostratic way, and the models are good approximations for describing the bulk microstructures of fCNFs.
06/01609 Modified activated carbons for catalytic wet air oxidation of phenol Santiago, M. et al. Carbon, 2005, 43, (10), 2134 2145. This study aims at testing several activated carbons for the catalytic wet air oxidation (CWAO) of phenol solutions. Two commercial activated carbons were used both as received and modified by treatment with either HNO3. (NH4)2SzOs, or H202 and by demineralization with HC1. The activated carbons were characterized by measuring their surface area, distribution of surface functional groups and phenol adsorption capacity. The parent and treated activated carbons were then checked for CWAO using a trickle bed at 140°C and 2 bar of oxygen partial pressure. The treatments increase the acidic sites, mostly creating lactones and earboxyls though some phenolic and carbonyl groups were also generated. Only (NH4)2S20~ treatment yields a significant decrease in surface area. CWAO tests show that catalytic activity mainly depends on the origin of the activated carbon. The modifications generally had a low impact on phenol conversion, which correlates somewhat with the increase in the acidity of the carbons. Characterization of the used activated carbon evidences that chemisorbed phenolic polymers formed through oxidative coupling and oxygen radicals play a major role in the CWAO over activated carbon.
06/01610 Tar yields from low-temperature carbonization of coal facies from the Powder river basin, Wyoming, USA Stanton, R. W. et al. International Journal of Coal Geology, 2005, 63, (1-2), 13-26. Tar yields from low-temperature carbonization correlate with the amount of crypto-eugelinite in samples selected to represent petrographically distinct coal facies of the Wyodak-Anderson coal zone. Tar yields from Fischer Assay range from < l to 11 wt% on a dry basis and correspond (r = 0.72) to crypto-eugelinite contents of the coal that range from 15 to 60 vol.%. Core and highwall samples were obtained from active surface mines in the Gillette field, Powder river basin, Wyoming, Because the rank of the samples is essentially the same, differences in low-temperature carbonization yields are interpreted from compositional differences, particularly the crypto-eugelinite content. In the Wyodak-Anderson coal zone, crypto-eugelinite probably was derived from degraded humic matter which absorbed decomposition products from algae, fungi, bacteria, and liptinitic plant parts (materials possibly high in hydrogen). Previous modelling of the distribution of crypto-eugelinite in the discontinuous WyodakAnderson coal zone indicated that tar yields should be greater from
coal composing the upper part and interior areas than from coal composing the lower parts and margins of the individual coal bodies. It is possible that hydrocarbon yields from natural coalification processes would be similar to yields obtained from laboratory pyrolysis. If so, the amount of crypto-eugelinite may also be an important characteristic when evaluating coal as source rock for migrated hydrocarbons.
05
N U C L E A R FUELS Scientific, technical
06/01611 A finite sub-element generalization of the variational nodal method Smith, M. A. et al. Progress in Nuclear Energy, 2004, 45, (2-4), 265, The variational nodal method is generalized by dividing each spatial node into a number of triangular finite elements designated as subelements. The finite sub-element trial functions allow for explicit geometry representations within each node, thus eliminating the need for nodal homogenization. The method is implemented within the Argonne National Laboratory code V A R I A N T and applied to twodimensional multi-group problems. Eigenvalue and pin-power results are presented for a four-assembly DECD/NEA benchmark problem containing enriched UO2 and MOX fuel pins. The seven-group model combines spherical or simplified spherical harmonic approximations in angle with isoparametric linear or quadratic sub-element basis functions, thus eliminating the need for fuel-coolant homogenization. Comparisons with reference seven-group Monte Carlo solutions indicate that in the absence of pin-cell homogenization, high-order angular approximations are required to obtain accurate eigenvalues, while the results are substantially less sensitive to the refinement of the finite sub-element grids.
06/01612 A heterogeneous coarse mesh solution for the 2-D NEA C5G7 MOX benchmark problem Forget, B. et aL Progress in Nuclear Energy, 2004, 45, (2~4), 233254. This paper presents a transport solution to the C5G7 2-D benchmark problem using a Monte Carlo adaptation of a heterogeneous coarse mesh transport method. The method couples Monte Carlo response function calculations to deterministic sweeps for converging the partial currents on coarse mesh boundaries. The propagation of statistical uncertainties is accounted for in a straightforward fashion. Presently, eigenvalue iterations have been avoided in order to investigate the impact of the partial current representation on the solution accuracy, Therefore, the results do not include the effect of residual eigenvalue error from actual outer iterations. However, excellent results have been achieved with very simple representations of the partial currents. In particular, the errors in the system multiplication factor and the average absolute pin power were 0.12% and 0.68%, respectively. The root mean square and the mean relative pin power errors were 1.15% and 0.56%, respectively. The largest discrepancies from the reference pin powers appeared in low power regions near the reflector, with a maximum error of 6.99%. The accuracy of the results of the coarse mesh method is comparable to most published fine mesh results. The deterministic iterations that actually solve the coarse mesh problem are extremely fast (of the order of seconds).
06/01613 Analysis of NEA C5MOX benchmark with computer code 'COHINT' based on interface current approach Mohanakrishnan, P, Progress in Nuclear Energy, 2004, 45, (2-4), 125131. Interface current approach to the solution of neutron transport equation has been used for LWR lattice problems. The analysis of the C5 MOX benchmark is an opportunity to test its applicability to heterogeneous reactor problems. Computer code COHINT, which incorporates a routine for solution of neutron transport equation in XY geometry by interface current approach was used for this analysis by representing the fuel rod as a square one. Region interface angular fluxes are represented by a four-term expansion. It is found that the average pin power error is about 2.28% (peak pin error 4.1%) relative to reference calculations. Further improvement is possible by introduction of the capability to represent circular rods with in a square cell in COHINT.
Fuel and Energy Abstracts
July 2006
249
06•01607 Mechanical and structural characterization of electrospun PAN-derived carbon nanofibers Zussman, E. et al. Carbon, 2005, 43, (10), 2175 2185. The mechanical and structural properties of individual electrospun PAN-derived carbon nanofibres are presented. EELS spectra of the carbonized nanofibres shows the C atoms to be partitioned into approximately 80% sp 2 bonds and approximately 20% sp 3 bonds, which agrees with the observed structural disorder in the fibres. TEM images show a skin-core structure for the fibre cross-section. The skin region contains layered planes oriented predominantly parallel to the surface, but there are some crystallites in the skin region misoriented with respect to the fibre long axis. Microcombustion analysis showed 89.5% carbon, 3.9% nitrogen, 3.08% oxygen and 0.33% hydrogen. Mechanical testing was performed on individual carbonized nanofibres a few microns in length and hundreds of nanometers in diameter. The bending modulus was measured by a mechanical resonance method and the average modulus was 63 GPa. The measured fracture strengths were analysed using a Weibull statistical distribution. The Weibull fracture stress fit to this statistical distribution was 0,64 GPa with a failure probability of 63%.
06•01608 Modeling of fishbone-type carbon nanofibers: a theoretical study Zhu, Y. A. et al. Carbon, 2005, 43, (8), 1694-1699. Five models for fishbone-type carbon nanofibres (f-CNFs) have been proposed and their geometries have been optimized through molecular dynamics and molecular mechanics simulations. The angle between graphene layers and fiber axis can take the values 9.71 °, 19.60 °, 30.03 °, 41.99 ° , and 56.43 ° , which agree satisfactorily with the experimentally determined values. With reduction of the angle, the interlayer spacing of graphene sheets increases fi'om 0.3376 nm to 0.3392 nm accordingly, due to the strain of the graphitic cones. In addition, X-ray diffraction (XRD) simulations are also implemented. With the high-resolution transmission electron microscopy (HRTEM) results taken into account, the X R D simulations verify that f-CNFs can adopt not only a regular arrangement but also a turbostratic way, and the models are good approximations for describing the bulk microstructures of fCNFs.
06/01609 Modified activated carbons for catalytic wet air oxidation of phenol Santiago, M. et al. Carbon, 2005, 43, (10), 2134 2145. This study aims at testing several activated carbons for the catalytic wet air oxidation (CWAO) of phenol solutions. Two commercial activated carbons were used both as received and modified by treatment with either HNO3. (NH4)2SzOs, or H202 and by demineralization with HC1. The activated carbons were characterized by measuring their surface area, distribution of surface functional groups and phenol adsorption capacity. The parent and treated activated carbons were then checked for CWAO using a trickle bed at 140°C and 2 bar of oxygen partial pressure. The treatments increase the acidic sites, mostly creating lactones and earboxyls though some phenolic and carbonyl groups were also generated. Only (NH4)2S20~ treatment yields a significant decrease in surface area. CWAO tests show that catalytic activity mainly depends on the origin of the activated carbon. The modifications generally had a low impact on phenol conversion, which correlates somewhat with the increase in the acidity of the carbons. Characterization of the used activated carbon evidences that chemisorbed phenolic polymers formed through oxidative coupling and oxygen radicals play a major role in the CWAO over activated carbon.
06/01610 Tar yields from low-temperature carbonization of coal facies from the Powder river basin, Wyoming, USA Stanton, R. W. et al. International Journal of Coal Geology, 2005, 63, (1-2), 13-26. Tar yields from low-temperature carbonization correlate with the amount of crypto-eugelinite in samples selected to represent petrographically distinct coal facies of the Wyodak-Anderson coal zone. Tar yields from Fischer Assay range from < l to 11 wt% on a dry basis and correspond (r = 0.72) to crypto-eugelinite contents of the coal that range from 15 to 60 vol.%. Core and highwall samples were obtained from active surface mines in the Gillette field, Powder river basin, Wyoming, Because the rank of the samples is essentially the same, differences in low-temperature carbonization yields are interpreted from compositional differences, particularly the crypto-eugelinite content. In the Wyodak-Anderson coal zone, crypto-eugelinite probably was derived from degraded humic matter which absorbed decomposition products from algae, fungi, bacteria, and liptinitic plant parts (materials possibly high in hydrogen). Previous modelling of the distribution of crypto-eugelinite in the discontinuous WyodakAnderson coal zone indicated that tar yields should be greater from
coal composing the upper part and interior areas than from coal composing the lower parts and margins of the individual coal bodies. It is possible that hydrocarbon yields from natural coalification processes would be similar to yields obtained from laboratory pyrolysis. If so, the amount of crypto-eugelinite may also be an important characteristic when evaluating coal as source rock for migrated hydrocarbons.
05
N U C L E A R FUELS Scientific, technical
06/01611 A finite sub-element generalization of the variational nodal method Smith, M. A. et al. Progress in Nuclear Energy, 2004, 45, (2-4), 265, The variational nodal method is generalized by dividing each spatial node into a number of triangular finite elements designated as subelements. The finite sub-element trial functions allow for explicit geometry representations within each node, thus eliminating the need for nodal homogenization. The method is implemented within the Argonne National Laboratory code V A R I A N T and applied to twodimensional multi-group problems. Eigenvalue and pin-power results are presented for a four-assembly DECD/NEA benchmark problem containing enriched UO2 and MOX fuel pins. The seven-group model combines spherical or simplified spherical harmonic approximations in angle with isoparametric linear or quadratic sub-element basis functions, thus eliminating the need for fuel-coolant homogenization. Comparisons with reference seven-group Monte Carlo solutions indicate that in the absence of pin-cell homogenization, high-order angular approximations are required to obtain accurate eigenvalues, while the results are substantially less sensitive to the refinement of the finite sub-element grids.
06/01612 A heterogeneous coarse mesh solution for the 2-D NEA C5G7 MOX benchmark problem Forget, B. et aL Progress in Nuclear Energy, 2004, 45, (2~4), 233254. This paper presents a transport solution to the C5G7 2-D benchmark problem using a Monte Carlo adaptation of a heterogeneous coarse mesh transport method. The method couples Monte Carlo response function calculations to deterministic sweeps for converging the partial currents on coarse mesh boundaries. The propagation of statistical uncertainties is accounted for in a straightforward fashion. Presently, eigenvalue iterations have been avoided in order to investigate the impact of the partial current representation on the solution accuracy, Therefore, the results do not include the effect of residual eigenvalue error from actual outer iterations. However, excellent results have been achieved with very simple representations of the partial currents. In particular, the errors in the system multiplication factor and the average absolute pin power were 0.12% and 0.68%, respectively. The root mean square and the mean relative pin power errors were 1.15% and 0.56%, respectively. The largest discrepancies from the reference pin powers appeared in low power regions near the reflector, with a maximum error of 6.99%. The accuracy of the results of the coarse mesh method is comparable to most published fine mesh results. The deterministic iterations that actually solve the coarse mesh problem are extremely fast (of the order of seconds).
06/01613 Analysis of NEA C5MOX benchmark with computer code 'COHINT' based on interface current approach Mohanakrishnan, P, Progress in Nuclear Energy, 2004, 45, (2-4), 125131. Interface current approach to the solution of neutron transport equation has been used for LWR lattice problems. The analysis of the C5 MOX benchmark is an opportunity to test its applicability to heterogeneous reactor problems. Computer code COHINT, which incorporates a routine for solution of neutron transport equation in XY geometry by interface current approach was used for this analysis by representing the fuel rod as a square one. Region interface angular fluxes are represented by a four-term expansion. It is found that the average pin power error is about 2.28% (peak pin error 4.1%) relative to reference calculations. Further improvement is possible by introduction of the capability to represent circular rods with in a square cell in COHINT.
Fuel and Energy Abstracts
July 2006
249