## 4 Results and Discussion
### Control Performance Analysis
#### 4.3.2 Linear Load Change  
The load-following performance was investigated by using the linear power change transient, in which the plant load is reduced from 100% FP to 50% FP at a rate of 5% FP/min, remains constant at 50% FP for 600 s, and then goes back to 100% FP at the same rate. The load signal, as the desired power, was sent to the control system, and the deviations of the measured values from the set values, \(\Delta N_{r}\) and \(\Delta T_{fo}\), were transmitted to the control system as error signals. Then, they were processed into a control signal and forwarded to the servo to drive the control rods.  
As shown in Figure 14a,c, the insertion of negative reactivity was achieved by the insertion of the control, which was executed by the control system, and then the thermal power was reduced following the desired value. Once the power reached the desired value of 50% FP at t = 650 s, the control system stopped the movement of the control rod, and then the power was kept constant for 600 s. After that, the power started to rise because of the extraction of the control rod, which was also executed by the control system, until it reached 100% FP. The reactor inlet and outlet temperatures were following the thermal power, as  
Figure 13: System responses to a step decrease in load demand: from 100% FP to 90% FP.  
can be observed in Figure 14e,f. In addition, the load signal sent to the control system was also used to maintain a constant steam outlet temperature. To achieve this purpose, the mass flow rate of the feedwater was adjusted to limit the temperature variation, as shown in Figure 14d. For the power reduction stage, since the power was reduced, less energy was transferred to the feedwater. So, the mass flow rate was reduced by the control system to maintain a constant steam outlet temperature. In the power increase stage, the mass flow rate was increased by the control system to extract more power from the reactor core with an unchanged steam outlet temperature. As illustrated in Figure 14, both the power and steam outlet temperature are highly consistent with the desired value. For the thermal power, the curve of the actual values almost overlapped with that of the desired values, and the steam outlet temperature was able to follow its set value within a difference of less than 1 K for the whole transient. A similar shape to that of the thermal power is observed for reactivity insertion by the control rod, since the thermal power is mainly adjusted by inserting positive or negative reactivity. The mass flow rate of the feedwater also has a similar shape, as the mass flow rate is approximately proportional to the transferred heat according to the energy balance. The inlet temperature changed within a range of 20 Km and the outlet temperature varied within a range of 90 K as a consequence of the power variation and heat balance, and the system parameters did not oscillate during the entire transient. The load-following capability of the control system is verified by the simulation results, as the thermal power is always capable of following its set value, and a constant steam temperature is maintained with a fluctuation of less than 1 K.  
Figure 14: System responses of the load-following change at a rate of 5%/min: from 100% FP to 50% FP.