Analysis of Impact on Vessel Water Level Measurement due to Post-LOCA Physical Phenomenon

To assess the validity of the L VSL (vessel water level) measurement of the CCMS (core cooling and monitoring system) in CPR1000 nuclear power plants under condition of LOCA (loss of coolant accident), the error of the L VSL measurement due to the post-LOCA physical phenomenon which may have impact on the measurement of dynamic and static pressures, and the special phenomenon in vessel-head was quantitatively calculated. The analysis results show that several minutes after discharging through the break, the error of the L VSL measurement induced by the special phenomenon in vessel-head and cold-leg or hot-leg break flow rate can be ignored. The flow rate of the break on the vessel-head and the stagnant water in the control rod guide tube will induce a significant over-estimated error to the L VSL measurement. The analysis combined with SOP (state oriented procedure) shows that the over-estimated error will not hinder the implementation of the safety important actions for accident management.