Option Study on a Steam Pressure Control Logic for SMART

Design features of SMART such as a large coolant inventory with a relatively low flow rate and the existence of a once-through steam generator require new steam control logic capable of coping with a prompt load change without inducing severe operational parameter fluctuations. A new MMS SMART model was developed to study the load-following capability and the system parameter manageability of three candidate control logics: the reactor leading, the turbine leading, and the feedwater leading logics. The MMS SMART model was composed of several interacting MMS modules with numerical data, each of which represented a component of the SMART plant and control logic. The Reactor Coolant System, and the Steam and Power Conversion System with their control logics were modeled using default modules such as a pipe, a pump, and a tank. The candidate control logics had been implemented in the model and their dynamic characteristics for the case of a 100%-50%-100% load-following operation with a 25%/min rate were examined. With the reactor-leading control logic implemented, the turbine power was changed with a considerable time delay, which was mainly due to coolant temperature signal retardation to the feedwater controller. The steam pressure variation was very limited for the reactor-leading control logic. With the turbine-leading control logic, the turbine power was manipulated well to match the reference value, whereas relatively large fluctuations of the steam pressure and the coolant temperature occurred. The steam pressure swung with a comparatively large amplitude and the peak value of the fluctuation was not reduced even with larger gain values of the PI controller. This steam pressure swing was considerably decreased with the feedwater leading control logic, while the reactor power and the coolant temperatures had similar trends to those of the turbine leading control logic.