Conceptual design of a high temperature power reactor cooled and moderated by supercritical light water

A high temperature reactor cooled and moderated by supercritical light water (SCLWR-H) is designed for assessing its technical feasibility and potential economic improvement. The plant system is the once-through direct cycle. Whole core coolant flows to the turbine. When adopting the conventional ascending flow type water rods, the cold coolant flowing up in the water rods is mixed with that of the fuel channel coolant above the core. Although the maximum surface temperature of the Ni-base alloy cladding is 620°C, the average core outlet temperature is low, 455°C. It, however, reaches 508°C in the core with the descending flow type water rods since no mixing of the coolant occurs above the core. The fuel enrichment is also decreased. The flow rate of each fuel assembly is controlled by an orifice to maximize the outlet coolant temperature. The reactor achieves high thermal efficiency of 44.0% and electric power of 1610 MW. The coolant flow rate per generated electricity is 24% lower than that of an Advanced Boiling Water Reactor (ABWR). This will reduce the size of the balance of plant (BOP) system. The burnup reactivity can be compensated by changing coolant flow rate ratio in the descending flow type water rods to the whole core through the fuel cycle. This reduces the number of control rods. The inlet and outlet coolant temperature and total flow rate need not be changed for keeping the power constant