Pressure and coolant mass changes diagrams for vessel blowdown.

Abstract

To provide a simple and efficient method to analyze blowdowns, generalized diagrams were provided which showed the changes of pressure and residual coolant mass on a dimensionless time scale. The dimensionless group rro was a parameter of the blowdowns shown in the diagrams which was given by the ratio between the energy increase rate due to heat generation and the decrease rate of the total internal energy due to coolant discharge through the break. The pressure and coolant mass changes drawn in the diagrams were obtained by analysis of the lumped energy and mass balances equations. The analysis for the subcooled water system indicated that the state change of the subcooled water during blowdown was approximated by an isothermal change. A comparison of the analytical and test results for the Two Bundle Loop showed good agreement in the pressure changes except at low pressure. Slowdowns with O:s; rr 0 :s; 1.0 were included in the diagrams for the two-phase mixture discharge and blowdowns with O:s;rro:s;O.l for the vapor discharge which covered typical BWR conditions. Correlation lines were also given in the diagrams which converted the changes in dimensionless time into those in real time.