Improvement of Feedwater Controller

The coolant outlet temperature and hence the main steam temperature are determined by the power to flow rate ratio in the core with constant inlet temperature. Thus, the change in the main steam temperature can be kept small by keeping the power to flow rate ratio constant. As shown in Fig. 7.72 [31], three feedback signals for the feedwater controller are proposed and added to (7.27) for that purpose. In this section, only the plant dynamics at BOEC is analyzed because there are almost no differences in plant dynamics between BOEC and EOEC. 

1 Feedback from Power to Flow Rate Ratio 

The first idea is that the deviation of the power to flow rate ratio itself is fed back to the feedwater controller. 

The improved control system with the feedwater controller described as (7.28) is designated Control system (A). The gain A p2a is tuned by analyzing the plant dynamics against the 10% stepwise decrease in the setpoint of the reactor power. The results are shown in Fig. 7.73 [31]. The changes in the power to flow rate ratio and the main steam temperature can be decreased from the case with the reference control system. 0.4 is chosen as Kp2 so that these changes are minimized. 

When the reactor power is higher than the rated value, the CRs are inserted and then the power will decrease. The opposite case is also expected. The second idea is that the deviation of the power is fed back to the feedwater controller too in order to make the flow rate follow the power. 

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