Effect of cascade overlap and C15 clusters on the damage evolution in Fe: An OKMC study
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Laves phase
Kinetic Monte Carlo
radiation damage
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Component (thermodynamics)
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ABSTRACTA nonconventional gas centrifuge cascade, called the NFSW (no feed and single withdrawal) cascade, is studied in the separation of middle components by means of numerical simulation. The cascade has no feed and only a single withdrawal at either end of the cascade, different from conventional cascades, which usually have two withdrawals at the two ends of the cascade and one feed in between. The material to be separated is loaded in a reservoir at either end, and the desired component is enriched in either the reservoir or the withdrawal at the other end. The effects of the unit separation factor (equivalently, the cascade length) and the ratio of the upstreaming flow rate to the withdrawal rate are investigated on separation. The separation performance is evaluated in terms of the material recovery and the operation time efficiency, and is compared with those of the corresponding conventional cascades and another type of nonconventional cascade, the SW (single withdrawal) cascade. It is found that the NFSW cascade is superior to the conventional cascade and comparable in the material recovery with, but advantageous in the operation time efficiency over the SW cascade.Key Words:: Multicomponent isotope separationGas centrifuge cascadeNonstationary cascadeNumerical simulation
Centrifuge
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The influence of surfaces on the evolution of damage of irradiated Fe is studied using object kinetic Monte Carlo with input from molecular dynamics simulations and ab initio calculations. Two effects are analysed: the influence of traps and the initial distribution of damage in the cascade. These simulations show that for a trap concentration of around 100 appm, there are no significant differences between defect concentrations in bulk and thin films. However, the initial distribution of defects plays an important role not only on total defect concentration but also on defect type, for the model used in this study. Damage produced by a 100 keV Fe ion impinging a Fe thin film. Blue (dark) spheres are self‐interstitials, red (light) spheres are vacancies.
Kinetic Monte Carlo
radiation damage
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A linear turbine cascade experimental apparatus often consists of only a few cascade blades. Advantages to this arrangement are increased from using larger cascade blades and easier optical access. However, fewer cascade blades in the cascade row make it difficult to establish periodic flow conditions between blades. In this study, a 160% pitch passage for cascade experiments with a single blade is designed to satisfy infinite cascade flow conditions without any flow control or tailboards. Fourteen geometric design variables are applied to the design of a 160% pitch passage by using a gradient-based optimization method and a genetic algorithm. Flow structures within a passage designed with a genetic algorithm are closer to the infinite cascade flow conditions than those obtained with a gradient-based method. The results show that infinite cascade flow conditions can be obtained by modifying only the passage walls of the cascade experimental apparatus.
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Most experimental work on radiation damage is performed to fairly high doses, where cascade overlap effects come into play, yet atomistic simulations of the primary radiation damage have mainly been performed in initially perfect lattice. Here, we investigate the primary damage produced by energetic ion or neutron impacts in bcc Fe and W. We model irradiation effects at high fluence through atomistic simulations of cascades in pre-damaged systems. The effects of overlap provide new insights into the processes governing the formation under irradiation of extended defects. We find that cascade overlap leads to an increase in the numbers of large clusters in Fe, while in W such an effect is not seen. A significant shift in the morphology of the primary damage is also observed, including the formation of complex defect structures that have not been previously reported in the literature. These defects are highly self-immobilized, shifting the damage away from the predominance of mobile 1/2〈111〉 loops towards more immobile initial configurations. In Fe, where cascade collapse is extremely rare in molecular dynamics simulations of individual cascades, we observe the formation of vacancy-type dislocation loops from cascade collapse as a result of cascade overlap.
radiation damage
Lattice (music)
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Abstract Data derived by the in-situ observation of microstructural evolution during heavy ion and electron irradiation carried out in the University of Tokyo in 1979–1986 have been re-examined and re-interpreted in the light of recent models of cascade-induced microstructural evolution. Cascade-induced vacancy dominance and its temperature dependence, and the enhanced sink strength caused by transient cascade clusters were suggested. These cascade effects may make it possible to explain the discrepancy in the free defect production efficiency derived by computer simulation, maximum void swelling rate and steady state radiation induced segregation or radiation enhanced diffusion. Key Words: Cascade effectsMicrostructural evolutionIrradiation correlation in-situ observation of radiation damage
Void (composites)
radiation damage
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Adaptive IIR filters implemented in cascade-form are attractive due to the ease with which their stability may be monitored. Four cascade-form structures are compared for use in adaptive filtering with respect to complexity of implementation, error surface geometry, and adaptation speed. The four structures include a cascade of second order pole/zero sections, a cascade of second order all-pole sections followed by a tapped delay line, and two new structures. The latter pair includes a tapped cascade, which is a cascade of second order all-pole sections whose output is constructed as a weighted combination of signals tapped from the cascade. The second new structure is a modification of the tapped cascade that yields orthogonal signals at the taps of the cascade. It is shown that the tapped cascade provides the best overall performance in the respects noted above.
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