Figure 4 Neutron Radial Flux Shapes for Bare and Reflected Cores

REACTOR OPERATION DOE-HDBK-1019/2-93 Reactor Theory (Reactor Operations) Figure 4 shows the general effect of reflection in the thermal reactor system where core power is proportional to the thermal flux. Notice that a reflector can raise the power density of the core periphery and thus increase the core average power level without changing the peak power. As illustrated in Figure 4, the thermal flux in the reflector may actually be higher than that in the outermost fuel since there are very few absorptions in the reflector. Varying the fuel enrichment or fuel concentrations in the core radially, axially, or both, can Figure 4 Neutron Radial Flux Shapes for Bare and Reflected Cores readily be used to control power distribution. The simplified example illustrated in Figure 5 shows the effect of using a higher enrichment in the outer regions of the core. Varying fuel concentrations or poison loading for flux shaping is frequently referred to as zoning. In the example illustrated the large central peak is reduced, but the average power level remains the same. Figure 5 Effect of Non-Uniform Enrichment on Radial Flux Shape NP-04 Rev. 0 Page 26