Safety Evaluation of Primary-Side Bleed-and-Feed Scenarios by an Experimental Loss of Feedwater Event at the IIST Facility

The current emergency operating procedures (EOPs) for a three-loop pressurized water reactor on a total loss-of-feedwater (LOFW) incident are experimentally evaluated at the Institute of Nuclear Energy Research Integral System Test (IIST) facility. Four experiments were conducted with a different number of pressurizer power-operated relief valves (PORVs) and centrifugal charging pumps (CCPs) engaged in performing the primary-side bleed-and-feed operation. In addition, the effect of opening a pressure vessel venting-path was also evaluated. The focus was on the effectiveness and adequacy of current EOPs and the observation of associated thermal-hydraulic phenomena. The test results indicated that the current EOPs can function well in mitigating the consequences of a LOFW event provided that at least two fully opened PORVs and one actuated CCP are used. The opening of a pressure vessel venting path during the bleed-and-feed operation is helpful in the primary system depressurization but has little effect to increase the pressure vessel coolant inventory. However, by opening one PORV, precaution for the reactor coolant system (RCS) integrity should be taken for system overpressurization caused by insufficient heat removal capability. Furthermore, an effective control of restored feedwater to a low injection rate is favorable to minimize the thermal stress in the RCS pressure boundary.