Heat removal capability of the Passive Residual Heat Removal (PRHR) system has been studied for application to new generation reactors. The PRHR system is one of the passive safety features which have been developed to enhance the reactor safety by nuclear vendor countries.
Effects of key design parameters of the PRHR system on its heat removal capability, i.e., size effect of inlet/outlet pipe flow areas and elevation effect of the PRHR heat exchanger have been studied. A series of physical calculations has been performed to obtain final attainable cooldown temperature and time required to cooldown RCS from hot standby to hot shutdown of 215.6℃(420˚F) below which Shutdown Cooling System (SCS) takes over continued RCS cooldown to a typical cold shutdown of 93.3℃(200˚F). Integrated system performance simulation with RELAP5, a computer program which has been used typically for nuclear power plant simulations, has been done to show RCS behaviors with the PRHR system operation, and thereby to prove that the PRHR system has a heat removal capability same as proven by physical calculations.
As a result of these calculations, it has been shown that the PRHR system has the heat removal capability which is required by US EPRI-URD. Relations between the initial natural circulation reactor coolant flowrate which can be established by PRHR design with a combination of the key design parameters and final attainable cooldown temperature which can be stand for heat removal capability of the system have been derived, and from these relations, it is concluded that larger heat transfer area of the PRHR makes the PRHR system more effective to cooldown RCS heat than larger inlet/outlet pipe flow area or higher elevation of the heat exchanger does.