The study of gravity makeup to RCS for the loss of RHR event during mid-loop operation

In case of the loss of residual heat removal system (RHR) event during mid-loop operation, one of the mitigation actions to prevent core uncovery is gravity makeup to the RCS. This study includes the mitigation actions for gravity makeup to the RCS for 3-loop nuclear power plant, minimum gravity makeup flow for prevention of core boiling and core uncovery and possible pass of gravity make up. Also, the evaluation of minimum gravity makeup to prevent core boiling and core uncovery was performed using the RELAP/MOD3.2.2beta code. The results of this study show that the minimum flow to prevent core uncovery in case of cold leg injection (about 20m3/hr) is too small to recover the core water level. So, our conclusion is that the minimum flow to prevent core boiling (about 170m3/hr) is enough to recover core water level