Figure 4.3.16 Control method for each wall thinning management rank

3. Upgrading by Facility Replacement

(1) Steam turbine

NPPs had always been operated at rated electric outputs until recently (constant operation at a rated electric output), but it has become possible to increase their electric output since amendment of the Electricity Utilities Industry Law in 1995 as long as the authorized reactor thermal power is not exceeded, and constant operation at rated thermal power has been performed since around 2002.

Since this constant operation at a rated thermal power has made it possible to increase electric output up to 5 % more than the authorized electric output depending on the capacity of the power generation facility, the plant thermal efficiency has begun to draw attention. With this trend, utilities’ attention has shifted from replacement of facilities focusing on conventional measures against degradation to active facility investment aiming at performance improvement and plant power increase, which has prompted applications of high efficiency technologies ranging from applications

of efficiency improvement technology to the steam turbine to replacement of brass tube bundles of the main condenser with titanium tube bundles.

Furthermore, as replacement of turbine facilities in BWR NPPs will generate radioactive waste, technologies to reduce radioactive waste generated by performing large-scale modification works on steam turbines, heat exchangers, etc. also have attracted further attention in recent years from the standpoint of on-site waste storage capacity.

(2) Electrical instrumentation and control components

Elements constituting the electrical instrumentation and control components (generator, motor, power supply facility, control equipment, instrumentation, computer, etc.) used at light water reactor power plants are the same as those used in thermal power plants and in general industries, and many of them are affected by aging although the effects depend on their service and environmental conditions. In particular, electronic devices,

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insulation materials, etc. cause malfunctions, functional decline and performance deterioration due to aging. For this reason, depending on service life for each component, its replacement or renewal is required during the plant lifetime. Generally it is said that electronics parts have a service life of about ten years.

Apart from direct effects due to aging, component renewal may be required since it becomes difficult to obtain compatible service parts and spare parts because of a shift from analog components to digital components, termination of manufacturing, etc., or it becomes hard to maintain a particular facility due to reduction in maintenance personnel with its expertise or its technology becomes obsolete. Particularly for electronic devices and parts including their elements, their technical progress and generational changes occur very fast

From such situations, it is important to manage electrical instrumentation and control components of light water reactor power plants by establishing maintenance programs, such as maintenance and inspection, and replacement / renewal programs of facilities according to their importance.

For establishing these programs, there are condition-based maintenance to perform maintenance and renewal according to conditions obtained by monitoring and diagnosing aging conditions of components and time-based maintenance to perform maintenance and renewal at predetermined intervals. It is important to establish the programs comprehensively taking into account reliability of monitoring and diagnostic technologies, the effect of a failure on operation, time and cost required to restore the failure, etc. for each component, and to reflect accumulated historical performance and knowledge of each component on the programs.

As monitoring and diagnostic methods for components, there are diagnosis of insulation degradation of generators and motors, monitoring of temperature, vibration and noise of rotating machines, self-diagnosis and error log analysis, etc. of electronics devices.

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