Design of Reference Fuel Rod and Core

the fuel and core of a 700 MWe class Super FR are designed as the starting point of improvements. The design goals, criteria, and methods are the same as those for the 1,000 MWe class Super FR described earlier in this chapter. 

2 Core Design Improvement for Negative Local Void Reactivity 

The coolant void reactivity calculated for the reference core is the overall void reactivity. Its definition is the change of reactivity when the coolant disappears from aU the fuel assemblies. The Super FRs are designed with closed fuel assemblies. No cross flow exists among the fuel assemblies. The local void reactivity, which is defined as the reactivity change when the coolant of one assembly disappears, needs to be kept negative throughout the cycle because there is possibility of a decrease in the coolant density in a particular fuel assembly. 

The mechanism of the local void reactivity is more complex than the overall void reactivity. Fuel assembly configurations and core configurations influence the distribution of the local void reactivity. The effects of those configurations on the local void reactivity of the Super FR are quantitatively investigated here. An example of the 700 MWe class core is designed, which has negative local void reactivity for all the seed assemblies throughout the cycle. 

Seed assembly G Fuel management group number 

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