The safety design and the analyses of pressure- and flow-induced accidents and transients of the direct-cycle supercritical-water-cooled fast reactor (SCFR) are discussed. The coolant system of the SCFR is the once-through type like a fossil-fired power plant. Maintaining the core flow is adopted as a fundamental safety requirement. The coolant flow rate is measured for the safety signal instead of the water level of a boiling water reactor. To guarantee the core flow, the plant is equipped with four high-pressure auxiliary feedwater systems, four low-pressure coolant injection systems, turbine bypass valves, and an automatic depressurization system.

Behaviors at pressure- and flow-induced events are analyzed by a computer code for assessing the safety of the reactor. Total loss of flow and pump seizure are considered as accidents, and the maximum cladding temperature criterion for stainless steel is satisfied. Flywheels are needed for the main feedwater pumps for prolonging the coastdown time more than 10 s. Six events are considered as transients. All results satisfy the minimum deterioration heat flux criterion. The loss of feedwater heating is not a severe transient, although there is no recirculation coolant. The loss of turbine load is not severe because the coolant flow is stagnated by closing turbine control valves, and the core power is reduced because of the decrease of the coolant density. The SCFR tolerates the pressure- and flow-induced events.