An Application of Main Steam Flow-Based Power Monitoring to OPR1000 Plants

It is extremely important in managing nuclear power plants to accurately confirm the thermal power of reactor for controlling and monitoring the plant power output. For pressurized water reactors (PWRs), feedwater flowrates have been typically used for mass and energy balance calculations to confirm the reactor thermal power. The feedwater flowrates are calculated from pressure drop measurements across venturis in plant feedwater systems. There have been so far many reports on the fouling of venturi, which has lead to erroneous high pressure drop measurements. This gives high mass flowrates, leading to high calculated reactor thermal power. The high calculated thermal power causes plant operators to reduce the power output to comply with the licensed operating power level. This causes losses in plant electrical output, typically about 2 ∼ 3% of the plant rating. One method to overcome the overestimation of reactor power due to high calculated feedwater flowrates due to venturi fouling is using steam flow measurements in reactor thermal power calculations. Plant operating experiences have shown that steam flows are a closer indicator of plant power. In addition they are known to show little fouling problem. A new power calculation methodology based on steam flow measurements is proposed herein for mass and energy balance calculations of reactor thermal power. A mathematical mass flowrate equation is developed for measured steam flows in a similar way to feedwater flows. The steam flow correction factors are determined from the operating data gained at the beginning of operation cycle. This is a way to calibrating steam flow measurements to feedwater flow indications to allow for the calorimetric heat balance to be based on steam flow rather than feedwater flow. Routine calibration testing procedure is developed to determine discharge coefficients for each operation cycle. The results of application to the Optimized Power Reactor 1000 (OPR1000) plants show good performance in plant power monitoring.