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Optimization for Setpoints of Steam Generator Water Level Control Systems in Power-uprated YGN 1 & 2 and Kori 3 & 4

Korean nuclear industry has performed power uprating project for YGN 1&2 and Kori 3&4 to increase the plant licensed power by 4.5%. The power uprating of 4.5% changes the plant operating conditions. Particularly, it reduces the capacity of steam dump valves from 70 to 59.1% of turbine steam flow at the full power. Thus, we evaluated the bounding transient of 95% load rejection as a function of a proportional band (PB) of SDCS whether the steam dump capacity was sufficient to accommodate the increased thermal load without the modification of component. Also, we performed the sensitivity studies for a PB of SDCS and a KPFM of FWCS to determine the optimized setpoints of FWCS and SDCS which minimized the fluctuation of steam generator (SG) water level due to swelling and shrinking. From these analyses results, we determined the optimized setpoints of FWCS and SDCS in power uprated YGN 1&2 and Kori 3&4. After then, we verified the appropriateness of these setpoints through analyzing SG level setpoint step change and turbine power ramp change. These verification analyses showed that the revised control setpoints of SDCS and FWCS were appropriate all over the plant normal operation range. Therefore, in order to accommodate the increased thermal load and to modulate SG water level stable, it was appropriate that the PB of SDCS set to 15.0 and the KPFM of FWCS to 0.6 in power uprated YGN 1&2 and Kori 3&4.