6.3 Density Difference and Loading Ratio Effects
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Fig. 6.30 Retention ratio under different loading modes
Fig. 6.31 stagnant ratio of middle and side pebbles
6.3.5 Retention of Initial Loading Pebbles
6.3.5.1 Retention Area
The stagnant zone plays an essential role in core safety and is not allowed to exist
in a real reactor core. To further investigate the relationship between the stagnant
condition and pebble densities, the flow of the initial loading 28,000 pebbles under
different loading modes was specially studied. Figure 6.32 depicts the cross-sectional
diagram of the retention region of the initial loading pebbles. The discharging rate
is set to be 1,000 pebbles per second and 28,000 pebbles would be discharged after
one cycle.
As seen in Fig. 6.32, lots of pebbles are still accumulating at the bottom after
35 s. Under the “H − L − H ” condition, the initial pebbles are all discharged at the
fastest speed with a relatively smaller retention area. On the contrary, the case of the
“L − H − L” configuration has the largest retention region.