Raising operator phase changes

In the Super LWR analyzed in Chap. 5, the coolant channels of all the fuel assemblies are cooled by upward flow, so that only one hot channel is treated in the thermal analysis and thermal hydraulic stability analysis. On the other hand, the coolant flow scheme in the reactor pressure vessel of the Super FR is the so-called two-pass scheme where part of the seed fuel assemblies and all the blanket fuel assemblies are cooled by downward flow as shown in Fig. 7.35. The fractions of the downward flow rate in the seed assemblies, blanket assemblies, and downcomer at the normal operating condition are determined in the core design as shown in Figs. 7.36 and 7.58 [26]. The flow distribution among those downward flow paths would change during the power raising phase so as to balance the pressure drops. 

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