This paper introduces the development of the current model Moisture Separator Reheater (MSR) for nuclear power plant (NPP) turbines, commercially placed in service in the period 1984–1997, focusing on the mist separation performance of the MSR along with drainage from heat exchanger tubes. A method of predicting the mist separation performance was devised first based on the observation of mist separation behaviors under an air-water test, then developed for the application to predict under the steam conditions, followed by the verification in comparison with the actual results of a steam condition test. The instability of tube drainage associated with both sub-cooling and temperature oscillation, which may adversely affect the seal welding of tubes to tube sheet owing to thermal fatigue, was measured on an existing unit both to clarify the behaviors and to develop a method to suppress them. Both methods were applied to current model MSR and the effectiveness of the methods was demonstrated. A new concept MSR for 1,700 MW class APWR units is put in perspective based on the technologies, alongside a multidisciplinary optimum design evaluating the heat exchanger tube bundle.

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