Steam Generator Liquid Mass as a Control Input for the Movement of the Feed Control Valve in a Pressurized Water Reactor

Abstract

The steam generator in a nuclear power plant plays an important role in cooling the reactor and producing steam for the turbine-generators. As a result, control of the water inventory in the steam generator is crucial. The water mass in the steam generator cannot be measured directly, so the water mass is generally inferred from the downcomer differential pressure as a measure of the downcomer water level. The water level in the downcomer is a good indication of the water mass inventory at or near steady-state conditions. Conventional PI controllers are used to maintain the water level in the downcomer between relatively narrow limits to prevent excessive moisture carry over into the turbine or the uncovering of the tube bundle. Complications arise in level control with respect to mass inventory due to the short-term inverse response of downcomer level. This is also known as shrink and swell. Due to the complications that arise from level control, one would like to directly control the mass inventory in the steam generator. Currently, the mass inventory is not a measurable quantity, but through the use of computer simulation can be calculated. Design and analysis of the new controller will be performed by simulation. The focus of this research was to develop and design, test, and implement a liquid mass inventory controller that would allow for safe automatic operation during normal and accident scenarios. In designing the new controller, it is assumed that the normal plant safety functions are not impacted by the mass controller. Optimal settings for the new mass controller are sought such that the mass control program will have rapid response and avoid reactor trips under automatic control if the downcomer level protection setpoints do not induce a trip for the same transient. For future analysis, it is proposed that neural networks be used in water mass observer instead of calculated simulation results.