Development of DLOFC Accident Analysis Function of DAYU

Abstract As a typical design basis accident (DBA) of High Temperature gas-cooled reactor (HTR), the Depressurized Loss Of Forced Cooling (DLOFC) accidents which will result in higher peak temperature receive more and more attention. The dynamics code for accidental system utility (DAYU) for HTR is developed by the Institute of Nuclear and New Energy Technology (INET) to conduct reactor accident analyses. DAYU is designed for thermal design and steady-state performance study, so the change of system pressure caused by the reduction of coolant inventory in the primary circuit can’t be characterized. In this work, the loss mass of coolant is introduced into the system pressure equation to characterize the pressure change process. In effect, the mass loss rate caused by the break will not only lead to the decrease of system pressure but also affect the flow direction of coolant in the primary circuit due to the different locations of the break, which will result in different temperature of the coolant that leaks out. Taking this phenomenon into consideration, the break mass flow rate is covered in the core flow field calculation further, which makes the simulation of the change of flow field in the reactor caused by the break mass flow rate become a reality. With these improvements, the DLOFC accidents analysis function of DAYU has been accomplished.