Modernizing steam turbines for nuclear power plants

Economic and safe operation of nuclear power plants requires reliable steam turbines with high efficiencies. The progress in flow mechanics achieved over the past few years has allowed the use of powerful methods of flow calculation in developments of new blading with greatly enhanced efficiencies. Thanks to the latest manufacturing techniques, the newly developed blading systems can be produced at low cost. Next to progress in flow mechanics, also the broadbased use of advanced finite-element calculations resulted in a more thorough grasp of the many problems associated with structural mechanics assessment of steam turbine components. The theoretical methods have been supplemented by comprehensive efforts in fracture mechanics and experimental materials studies, thus helping to create a reliable knowledge base which will help to avoid the dreaded stress corrosion cracking phenomenon, in components of steam turbines. The measures introduced to improve operational reliability already in design and manufacture have been supplemented by modern measurement techniques. Thus, e.g., a system for contactless measurements of blade vibrations allows continuous blade monitoring while the steam turbine is in operation. All these advances are being used successfully in upgrading steam turbines for nuclear power plants. The article contains descriptions of the measures taken to increase efficiency, operational reliability, and service life, and includes a forecast of further improvements to be expected especially in increases in efficiency. A survey of past and planned revamping measures in nuclear power plant turbines confirms the validity of this approach. (orig.)