Mode K - A Core Control Logic for Enhanced Load-Follow Operations of a Pressurized Water Reactor

New core control logic known as Mode K has been developed to enhance the load-follow operation (LFO) capability of a pressurized water reactor. The Mode K reactor regulating system, which actuates control bank movements, consists of two closed control loops, one for the coolant average temperature control and the other for the axial power shape control. Via its peculiar logic for selecting the control banks to be driven, the Mode K controls the coolant average temperature and axial power shape simultaneously and automatically within their allowed operating limits. In this way, the Mode K significantly reduces the operator burden associated with conventional manual power shape control during LFOs. A simple and flexible soluble boron scenario complements the Mode K logic and contributes toward reducing operational burden by its simplicity. The Mode K logic has been implanted in the Korean Next-Generation Reactor, a 1300-MW(electric) class evolutionary nuclear power plant under development in Korea, and various kinds of LFOs including frequency control have been simulated using the Framatome engineering simulator SAPHIR. The simulation results show reasonable core control performance of the Mode K as well as proper behaviors of other major nuclear steam supply system components such as the pressurizer and steam generator.