Core design of a high-temperature fast reactor cooled by supercritical light water

A high-temperature large fast reactor cooled by supercritical water (SCFR-H) is designed for assessing its technical feasibility and potential economical improvement. The coolant sys- tem is once-through, direct cycle where whole core coolantflows to the turbine. The goal is to achieve the high coolant outlet temperature over 500 C. We study the reactors with blankets cooled by ascending and descendingflow. SCFR-H adopts a radial heterogeneous core with zirconium-hydride layers between the driver core and the blankets for making coolant void reactivity negative. The coolant outlet temperature of the core with blankets cooled by ascendingflow is low, 467 C. The reasons are as follows: (1) the power swing due to the accumulation of fissile material in the inner blankets with burn-up, and (2) local power peak in the assemblies due to the zirconium-hydride layers. The di€erence in the outlet coolant temperature is more enhanced than the low temperature core where outlet temperature is approximately 400 C. The reason is that the coolant temperature is more sensitive to the enthalpy change than near the pseudo critical temperature, 385 C at 25 MPa. Thus, we design the core with blankets cooled by descendingflow to obtain high coolant outlet temperature. The coolant outlet temperature becomes 537 C, which is 70 C higher than that of the core with ascending blanketflow. The thermal eciency is improved from 43.2 to 44.6%. The coolant massflow rate per electric power decreases by 14%. This will reduce the size of the balance of plant (BOP) system. The power of the reactor is high (1565 MWe) and the void reactivity is negative.