731 research outputs found
The design and thermo-structural analysis of target assembly for high intensity neutron source
The engineering design of an integrated target assembly of IFMIF lithium target was performed in IFMIF/EVEDA project for a high intensity neutron source. In the evaluation of the design, a thermos-structural analysis of was evaluated by ABAQUS code, and the modeling region was a part of the target assembly which was from the inlet nozzle to the outlet pipe. The material of the target assembly including the back plate was F82H steel. In the thermal-structural analysis, the normal operations and start/stop or abnormal operations were evaluated at 250 or 300 °C operation of Li flow in inlet pipe. The result showed that the temperature of the target assembly was evaluated to be still lower than the Li boiling point of 344 °C under a vacuum pressure of 10−3 Pa. In a temperature constant operation, the calculated stresses and displacements were small enough for thermal soundness of the target assembly in steady states. In a transient cooling process from 300 °C to 20 °C through 250 °C, the maximum Mises stress was found to be 372 MPa, which was lower than the yield stress at 300 °C. Keywords: High intensity neutron source, Target assembly, Thermo-structural analysis, Li target, IFMIF, F82
Strain in the mesoscale kinetic Monte Carlo model for sintering
Shrinkage strains measured from microstructural simulations using the
mesoscale kinetic Monte Carlo (kMC) model for solid state sintering are
discussed. This model represents the microstructure using digitized discrete
sites that are either grain or pore sites. The algorithm used to simulate
densification by vacancy annihilation removes an isolated pore site at a grain
boundary and collapses a column of sites extending from the vacancy to the
surface of sintering compact, through the center of mass of the nearest grain.
Using this algorithm, the existing published kMC models are shown to produce
anisotropic strains for homogeneous powder compacts with aspect ratios
different from unity. It is shown that the line direction biases shrinkage
strains in proportion the compact dimension aspect ratios. A new algorithm that
corrects this bias in strains is proposed; the direction for collapsing the
column is determined by choosing a random sample face and subsequently a random
point on that face as the end point for an annihilation path with equal
probabilities. This algorithm is mathematically and experimentally shown to
result in isotropic strains for all samples regardless of their dimensions.
Finally, the microstructural evolution is shown to be similar for the new and
old annihilation algorithms.Comment: 6 pages, 6 figure
Anomalous Crossing Frequency in Odd Proton Nuclei
A generic explanation for the recently observed anomalous crossing
frequencies in odd proton rare earth nuclei is given. As an example, the proton
band in Ta is discussed in detail by using the
angular momentum projection theory. It is shown that the quadrupole pairing
interaction is decisive in delaying the crossing point and the changes in
crossing frequency along the isotope chain are due to the different neutron
shell fillings
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