Abstract
In nuclear power plant, By-pass System-A (named TSA) provides an artificial load during condenser steam dump unavailability or failure and in order to reduce the magnitude of temperature and pressure transients on the NSSS (Nuclear Steam Supply System). TSA system has some safety functions such as protection against overpressure or excessive heat up of reactor coolant system and protection against excessive cooling and safety shutdown and fast cool down. In TSA system, the most important equipment is steam dump valve which is powered by compressed air and could control flow mass through regulating valve travel. In order to know more about flow characteristics of TSA system, it's very important to know the relationship between flow mass, inlet pressure of valve (secondary loop pressure) and valve travel. In the paper, a model including steam dump valve, silencer and pipes is built and a numerical method is used to research the relationship between flow mass, valve travel and inlet pressure. During research, we found that outlet pipe reached a supercritical state when fluid is flowing from valve to silencer and a phenomenon of blocking flow is appeared in the valve. In Consideration of critical flow and blocking flow, we use a numerical simulation method to get the relationship between flow mass and valve travel and valve inlet pressure. The numerical method in this paper can provide ideas and basis for solving similar problems in engineering. The research results have an important reference value on selecting regulating valves.
