Center-voids

In Fig. 25b, the simulated marker particles were released from the bottom surface, which generates path lines that show more detail of the flow inside the WS, at lower radial coordinate values. The path lines reinforce the trends seen in Fig. 25a, and it is also possible to see some evidence of flow through the center voids of the particles. Most evident is the mix of spiraling and axial flow between the center front and center right particles. 

The present method recommended by this major industrial account is to disconnect the center-voided column, grasp it in one hand, and rap the counter with it twice, reverse the column, and do the same with the other end. Obviously, not hard enough to bend the column Hook it up backwards and run it at high flow rate for a minute or two. Then run the four-standard mixture. The column is run reversed from then on. It is possible that an end void may be formed yielding rabbit-eared split peaks, and must be repacked, but the column bed should be restored. 

A center void probably occurs because small wall and bed voids link up under pressure changes and shock to form a channel. The channel is a path of least resistance and diverts the flow from the bed. This effectively removes this part of the column from the separation and gives a shorter column and shorter retention times. Eventually, the whole column is channeled and you have a center void the length of the column. If you have ever run a gravity-fed, packed glass column, you have probably seen this channeling phenomena if you accidentally let the column run dry. 

Voids—Spaces or openings in the column bed leading to poor chromatography. End voids are directly under the inlet frit. Center voids are channels through the center of the packing bed. 

In Fig. 12 these three different nets are shown with the P points in the voids of the G-net and the N-net marked by squares. The axis of the unit cell has to be enlarged by the factor for the G-net and by a factor of 2 for the N-net with respect to the primitive lattice, formed by centering voids. The first case is indicated by the subscript V, the second case by the subscript 2, actually it should be 22 for ax, 2- Therefore the following equations can be written ... 

Credit for the center void is expressed as a geometric correction factor. In the current design, a center void near 56 mils in diameter (assuming a gap conductivity of 1500 Btu hr-ft -°F) gives a 20 % increase in allowable linear power. This is possible considering fuel densification alone and has often been observed experimentally. 

The prompt-neiitron decay constants obtained from the Rossi- measurements with toe anntdar cylinders at delayed critical are somewhat smaller than those obtained for solid uranium metal assemblies since the flight time of the neutrons across toe center void constitutes a large fraction of toe prompt-neutron lifetime. At delayed crit-... 

Reactor fuel shipping cask that has a center void divided into four sections by a boron steel cruciform. Three poisoned canisters, each containing 12 fuel elements, are stacked into each cask section for a total of 144 elements in the cask. Previous mqperimental results had indicated that criticality could be achieved wider optimum conditions (without poison) with approximately 25 of the 2.1 wt% fuel elements. Using HAMMER/Head, ... 

A center void occurs because of the large energies required to bend the graphene sheets into smaller circumferences. 

Figure 2 shows the three fuel regions and a center void region in the model. The outer region. III, is material that is below the sintering temperature, and retains its fabricated density. The material is assumed to be nonplastic and brittle, and tends to move outward as a result of thermal expansion. 

Actually, the power is also affected by the initial density which determines both the thermal conductivity and the center void diameter. Furthermore, thermal expansion tends to reduce the central void. Since both high density-high conductivity and high porosity-large void... 

The fuel pin temperature pattern as a function of burnup is influenced by the effect of fuel management on the neutron flux distribution. An indication of trends is shown in Fig. 3 for an idealized case where the linear pin power is maintained at a constant value of 16.2 kW/ft. The temperature gradient across the gas gap increases as fission gases dilute the helium in the gap. An increase in the center void is also expected with burnup with a resulting lowering of the maximum temperature. In the actual case, however, the effects of fuel cracking and restructuring could lead to a different pattern. 

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