Simulating the Sliding Control Modes in the Secondary Coolant Circuit of an NPP with a VVER-type Reactor

Abstract

The aim of the work is to investigate the possibility of achieving better maneuverability of VVER-type NPP units by introducing a sliding control of main steam pressure without significantly affecting their efficiency. To this end, a method that helps avoid reduction in steam saturation temperature, which is the key drawback of the sliding mode at NPPs, is proposed. According to the proposed methodology, the secondary thermal cycle circuit is supplemented with a water–steam superheater, which utilizes the heat released during reactor unloading for additionally superheating the steam at the steam generator outlet. Mathematical modeling of the superheater itself and the power unit power performance indicators were mathematically simulated in the constant and sliding pressure control modes. The article presents the calculated power performance indicators of the steam turbine and the unit as a whole, and their comparative assessment, which has confirmed the effectiveness of the proposed technical solution. It has been demonstrated that in the case of using sliding control with additional steam superheating, the turbine power output produced at reduced loads with maintaining the steam temperature downstream of the superheater at its nominal value, exceeds the power in the base mode (at constant pressure) by 5.0–9.0%. The study results can be used in modernizing the existing and designing new nuclear power units with VVER reactors to expand their operating range in maneuvering modes, which is of relevance under the conditions of the growing share of unstable generation in the power system.