Increasing the Power Output of VVER-Based NPPs through More Accurately Monitoring the Thermal Efficiency Indicators

Monitoring of thermal efficiency is of utmost importance for securing efficient NPP operation. To this end, the measurement instruments should have accuracy sufficient for the possibility of determining the actual values of thermal cycle circuit parameters, thermal efficiency, and deviations of the turbine set characteristics from their standardized indicators. The error with which the reactor thermal power is determined using the reactor core thermal-physical parameters and the steam generator parameters is estimated. It is shown that the best accuracy of determining the reactor thermal power can only be achieved through improving the accuracy of determining the steam generator thermal power. An analysis has shown that the error of determining the reactor thermal power is by more than 95% due to the error of determining the feed water flowrate. If we succeed in achieving more accurate determination of the reactor thermal power, it will be possible to obtain more accurate data on the electricity generation during operation at the nominal parameters in the mode with a specified neutron power due to maintaining of the reactor plant’s actual thermal power closest to its design value; in addition, it will be possible to extend the range of power outputs available for operation during operation in the mode of maintaining the specified electric power output by increasing its maximal value. Given the specified period of NPP operation, the maximum of its energy production serves as one of the criteria for economically efficient NPP operation. By using the developed mathematical model of the turbine set used in the NPP constructed according to the AES-2006 conceptual design (with a VVER-1200 reactor), the authors have revealed the effect of the error of determining the thermal cycle circuit parameters on the power unit electric power output and the parameters that have the highest influence on the error of estimating the electric power output. The influence of the error of determining the turbine thermal parameters, moisture separation and steam reheating, high- and low-pressure regeneration, and the turbine set low-grade heat part was analyzed, and the total error of determining the electric power output has been obtained based on the analysis results. These data make it possible to formulate the requirements for the accuracy of flowrate, temperature, and pressure measurements depending on the allowable error of determining the electric power output. An analysis of the operational data of the Leningrad-2 NPP, Novovoronezh-2 NPP, and Belarussian NPP power units has shown that the potential of increasing the electric power output due to improved accuracy of determining the thermal cycle circuit parameters makes 10–15 MW.