Comparative study between cold leg and hot leg safety injection during SBLOCA in a 4-loop PWR NPP

This article presents a comparison between two operation modes for the emergency core cooling system during a Small Break Loss of Coolant Accident (SBLOCA) in the cold leg of 4-loop PWR Westinghouse design nuclear power plant. In the first mode, the cold leg safety injection is used to mitigate the consequences of the accident and in the second mode the hot leg safety injection is used. The best estimate light water reactor transient analysis system code RELAP5 Mod3.3 was used in calculations. The plant nodalization consists of two loops; the first one represents the broken loop and the second one represents the other three intact loops. The results show that, in the cold leg safety injection the primary pressure decreases with time and remains higher than the secondary pressure for a period of time (~ 500 sec) during whichthe steam generators remains as a heat sink for the primary side, the accumulators start late and functioning on remaining transient time, and a repeatable loop seal clearing and refill occurs. During the hot leg safety injection the primary pressure decreases rapidly but remains higher than the secondary pressure for a longer period of time (~ 600 sec), the accumulators start early and functioning on a part of the transient time before they are totally discharged, and there is no repeatable loop seal clearing and refill. In the two modes the maximum clad surface temperature does not violate the safety limit.