Jun Manabe

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.

Flow Instability Inside Heat Transfer Tubes of MSR

Moisture separator reheater for nuclear steam turbine system of light water reactor, a combined equipment of mist separator and in-tube side condensing multi-tube type heat exchanger, has an inherent issue of flow instability inside the tubes. The issue causes the temperature oscillation and possible thermal fatigue at tube to tube-sheet welding of the tube outlet end. Construction of its heat transfer is that heating main steam supplied by NSSS inside the tubes transfers its latent heat by condensing to the colder high pressure turbine exhaust steam cooling outside of the tubes. The condensed water is exhausted by friction of venting excess steam through the tubes which makes the flow in tubes gas-liquid two phase regime and results the steady drainage without sub-cooling and associated temperature oscillation at tube end. A measuring was conducted on MSR of an existing 600 MW class unit to clarify the unstable behaviors without excess steam, which showed the temperature oscillation at tube end with synchronizing to oscillation of both pressure difference between tube inlet and outlet chambers and tube surface temperature along the tube. The cycle and the amplitude of the temperature oscillation were 55 second and 40K. Only the effects of venting steam for the actual unit and presumption of the mechanism of subcool were reported in the original paper, Journal of Engineering for Gas Turbines and Power 2010 Vol. 132/ 102905, here is added qualitative and quantitative study for both dynamics of the condensed water and behavior at tube outlet end to assess adequacy of the mechanism.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

Refurbishment of Secondary System and High AVT Water Treatment of Genkai #1 and #2

Kyushu electric co. Genkai #1 and #2 are twin 500 Mw class first generation PWR power stations starting their commercial operation in 1975–1981. The units were recently altered their secondary water treatment from AVT to HAVT (High All Volatile Treatment) operation aiming to suppress erosion in piping and equipment, resulting in feed water iron concentration reduction to around 1 ppb as indication of the effects. The units had been successfully operated from the start of their commercial operation except for scale adhesion to SG and others, degradation of copper alloy material tubes in auxiliary heat exchangers and lower condenser vacuum derived from protective ferrous sulfate coating. Life cycle management program was implemented resulting in the alteration of water treatment to HAVT adopting the SG blow down demineralizing and the replacement of copper alloy tube heat exchangers to stainless steel and titan tubes. Further more the examination results were introduced, of the scale adhesion mechanism in the high temperature region of the secondary system based on actual plants iron characterization data and field examination results of HAVT of Genkai units, expecting HAVT application would be effective for the scale adhesion reduction.Copyright