shows the axial distribution of coolant density and the density coefficient of that
core. The sodium density coefficient (%Δk/kk
0 /Δρ) in the sodium plenum becomes
positive. On the other hand, sodium density change (Δρ) in the sodium plenum
becomes negative because of the increase of coolant temperature for an accident
such as ULOF (unprotected loss of flow accident). Therefore, net sodium void
reactivity becomes negative.
The mechanism for reducing sodium void reactivity of the core is that the axial
neutron leakage is largely enhanced with coolant voiding in the sodium plenum. It
is known that the evaluated leakage component of sodium void reactivity with
diffusion theory might be overestimated by about 50 %. Therefore, calculation
Fig. 17.1 Dependency of sodium void reactivity on minor actinide (MA) content
Fig. 17.2 Core configuration of the homogeneous MA-loaded core
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T. Takeda et al.