Study on Thermal Hydraulic Characteristics of Two-phase Discharge Process under Different Initial Events

This paper studies the complex two-phase thermal hydraulic process after the opening of the pressurizer safety valve so as to determine the two-phase discharge characteristics of the pressurizer safety valve under different initial events. In this paper, the autonomous system analysis program ARSAC is used to model and analyze the upstream and downstream of the pressurizer safety valve, and three typical valve discharge processes are selected, including the accidental opening of the pressurizer safety valve, the complete loss of main steam flow that causes the opening of one or more safety valves, and the accidental starting of the safety injection pump that causes the intermittent opening of the pressurizer safety valve under the condition of low temperature overpressure protection. The complex two-phase thermal hydraulic characteristics involved in the process of water seal and steam (or water) discharge after the opening of the pressurizer safety valve are studied. The results show that the ARSAC program can capture the flow pattern changes in the pipeline during two-phase discharge; the water seal will form an obvious flow peak through the downstream pipeline, and the flow peak and time characteristics of the downstream pipeline caused by the discharge process are different under different upstream initial conditions. The study in this paper can provide guidance for load analysis, safety evaluation and design optimization.