Rapid depressurization capability of safety depressurization system for total loss of feedwater event

The Ulchin nuclear power plant units 3 and 4 envisions a Safety Depressurization System (SDS) similar to that of ABB-CE's System 80+ to mitigate the beyond design basis event of Total Loss of Feedwater (TLOFW). This paper presented the results of a best estimate analysis to determine the bleed capacity of the SDS for Ulchin 3 and 4. variations in the analytical bleed area was investigated as well as the time of operator action relative to the pressurizer safety valves opening time. The cases included the representation of a failure of one bleed path and a High Pressure Safety Injection Pump (HPSI). The capacity equivalent to an analytical area of 0.018 ft2 per bleed path was found to be the minimum capacity to prevent core uncovery if operator initiated Feed and Bleed operation properly