In nuclear plants, feedwater flow is utilized to calculate the heat input to the Nuclear Steam Supply System (NSSS). The heat input, in conjunction with a heat balance around the reactor, is used to calculate the reactor core thermal power. Since a calibrated flow nozzle is used to measure feedwater flow and, the calibration assumes a clean flow section with no fouling, any deposits or fouling of the flow nozzle will result in errors in flow measurement, causing the flow to read high. This would result in a calculated reactor power higher than the true value and an attendant loss in plant capacity. The paper presents the methodology and heat balance techniques used in diagnosing the existence of feedwater flow nozzle fouling and in quantifying the capacity loss. The paper provides recommendations on how to monitor performance for tell-tale signs of feedwater flow nozzle fouling and steps to take for corrective action.

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