Issaku Fujita

Recent Moisture Separator Reheater Design Technologies

The moisture separator reheater (MSR) is a key piece of equipment in reheat systems in nuclear steam turbines that use saturated main steam, where it helps improve turbine efficiency and suppress flow-accelerated corrosion. Fundamental to achieving a compact, reliable MSR design are methods for predicting mist separator vane performance and suppressing tube drainage instability. First, we devised a method for predicting separator performance based on the observation of mist separation behavior under an air-water test. We then developed a method for predicting performance under steam conditions from air-water test data and verified it by means of a comparison with the actual results of a steam condition test. The instability of tube drainage associated with both subcooling and temperature oscillation at turbine partial load, which might adversely affect the seal welding of the tubes to the tube sheet due to thermal fatigue, was measured on an existing unit to clarify the behavior. We then developed a technique for increasing venting steam, which had been operating at a constant flow rate, to suppress instability and verified its effectiveness. Both methods were applied to current MSR models, which were adopted for nuclear power plant turbines commercially placed in service from 1984 to 2009, and the effectiveness of the methods was demonstrated. The separator vane mist carryover rate was less than 0.1 %, and tube drainage instability was suppressed, demonstrating the effectiveness of the simple design concept of a two flow U-tube instead of the prevailing four-flow U-tube design. We put forth a new concept in the design of MSRs for 1700 MW class advanced pressurized water reactor (APWR) units based on associated technologies, along with advanced technology for the compact design of pressure vessels and multidisciplinary optimum design for evaluating heat exchanger tube bundles.

Experimental Study on Condensate Inundation for Condensation of Horizontally Flowing Steam in a Large Condenser Tube Bundle

While 1700MW class Pressurized Water Reactor (PWR) projects like US-APWR are conducted by Mitsubishi Heavy Industry (MHI) now, the size of condenser tube bundle becomes the largest ever constructed by MHI to be accordance with the increased heat rejection rate from the turbine system. Where, it becomes difficult to ignore the condensate sub-cooling and heat transfer deterioration by condensate inundation. Therefore, we have been working on research about the practical application of large-sized condenser since 2008, and tube arrangement optimization is one of the important subjects.As suitable tube arrangement for a large-sized condenser, the proven streamlined shape tube bundle was proposed, which had been adopted in the fossil fuel power units. In the streamlined shape tube bundle, most steam condenses on tubes under horizontal or downward steam flow conditions. In large tube bundle, the heat transfer deterioration due to inundation apparently occurs. On the other hand, condensate is blown away by the horizontal steam flow, and the effect of inundation would be reduced. For the tube arrangement optimization, the accurate knowledge on heat transfer including the behavior of such condensate under the horizontal steam flow condition is essential. However, most research on steam condensation on tube bundle has been conducted for the downward steam flow but the research for horizontal steam flow condensation is very limited so far (1–5).In the present research, condensation experiments were conducted by using a horizontal tube bank containing 36 cooling tubes with 12 condensate supply tubes. Steam was horizontally supplied to the tube bank at velocities 15–27m/s at pressures of 8.8kPa. Cooling tubes were made of copper and have an outer diameter of 19.1mm and condensing length of 150mm. In order to clarify the effect of condensate inundation on condensation heat transfer in detail, local heat transfer coefficients and the condensate flow in the tube bank were measured. In this paper, we describe findings on the condensate behavior and heat transfer in horizontal flow obtained by the experiment.Copyright

Recent Design Technologies of Moisture Separator Reheater

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.Copyright

Development of High Performance Moisture Separator Reheater

Moisture Separator Reheaters (MSRs) of Nuclear power plants, especially 1st generation type (commercial operation started from between 1970 and 1982), has been suffered from various problems like severe erosion, moisture separation performance deterioration, drain sub cooling. To solve these problems and performance improvement, improved MSR was developed. At the new MSR, high performance SS439 stainless steel round type tube bundle was applied, where heating steam distribution is optimized by orifice plate in order to minimize the drain sub cooling. Based on the CFD approach, cycle steam distribution was optimized and FAC resistant material application for the internal parts of MSRs was determined. As a result, pressure drop was reduced by 0.6% against the HP turbine exhaust pressure. Performance of moisture separation was improved by the latest chevron type separator. Where, the reverse pressure is locally caused at the drainage area of the separator because remarkable longitudinal pressure distribution is formed by the high-speed steam flow in the manifold. Then, a new moisture separation structure was developed in consideration of the influence that this reverse pressure gave to the separator performance.© 2009 ASME