Comparison of Improved Feedwater Controllers

The reactor power is not sensitive to the flow rate because the Super FR is a fast reactor with small reactivity feedback from coolant density. The reactor power is mainly regulated by the CRs. Therefore, the responses of the reactor power do not significantly differ with the four control systems including the reference one. Since the responses of the core and main steam pressures are very fast and determined by only the turbine control valves, they are almost the same with the four control systems. The changes in the main steam temperature obtained by the plant stability analyses are summarized in Table 7.37 [31]. The advantages and the issues of each control system are discussed below. 

Control system (B), where the reactor power is fed back to the feedwater controller, keeps the main steam temperature more stable than the reference control system when the power level is changed by the CRs as in Fig. 7.76 [31]. However, this control system gives similar plant dynamics to those with the reference control system unless the reactor power is significantly changed by the CRs. This is because the reactor power is less sensitive to the flow rate and mainly influenced by CRs. 

The feedwater controller of Control system (C) also makes the flow rate follow the reactor power. When the change in the power is caused by CRs, this control system works better than the reference control system as evinced in Fig. 7.76 [31]. When it is caused by the reactivity feedback from the coolant density, the change in the main steam temperature is larger than the reference cases as in Figs. 7.79 [31] and 7.80 [31]. 

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