Plant control of high temperature reactor cooled and moderated by supercritical light water

In this paper, dynamic behavior and plant control system of high temperature supercritical-pressure light water cooled and moderated reactor (SCLWR-H) with descending flow water rods are described. The SCLWR-H has no recirculation system. The core flow rate is less than 1/7 of BWR. In the core there is 3-5 times larger density change than in a BWR core. Thus, the dynamic behavior of the SCLWR-H is different from that of BWR. It is also different from that of a once-through supercritical light water cooled fossil-fired power plant (FPP) because of reactivity feedbacks. The dynamic behaviors of the SCLWR-H and a low temperature fast reactor (SCFR), which was analyzed in the past study, may be also different each other because of the water rods, differences in the coolant density coefficient, and difference in the density change in the cores. Step responses of the SCLWR-H are calculated against the perturbations of reactivity, flow rate and pressure. The moderator in water rods makes core power not sensitive to the change of feedwater flow rate. The water rods contain about 76% of the volume of the total water in the core and its density is not sensitive to the flow rate. The plant control system is designed according to the step responses. The turbine inlet pressure, the main steam temperature, and the core power are controlled by the turbine control valves, the feedwater pumps and the control rods, respectively. The parameters of the control system are optimized by the test calculations to satisfy the criteria of both fast convergence and stability. The SCLWR-H plant is controlled stably with the designed control system against various perturbations, such as setpoint change of the pressure, the main steam temperature and the core power, decrease in the feedwater temperature, and decrease in the feedwater flow rate. (author)