For the safe and stable operation of nuclear power plants over a long period of time, it is important to continuously maintain the integrity of equipment, improve safety and reliability and increase operational sophistication. The implementation of a digital instrumentation and control system is an answer to such effort. In the instrumentation and control systems of modern pressurized water reactor (PWR) plants, digital technology is already employed in all the control equipment including the main control board in order to improve safety, reliability and maintainability. On the other hand, analog equipment is still used in the reactor control and protection systems of operating plants built from the 1970s to the 1990s. Looking ahead to the operation of nuclear power plants for more than 40 years, we are proceeding with the digital upgrade of such analog equipment and have already completed the work at 20 plants. For digital upgrade, we developed a universally applicable standardized system architecture and verified its applicability together with electric power companies. Our upgrade services can be tailored to meet the varying needs of electric power companies and realize high reliability and maintainability. For example, we can provide not only upgrades of all the equipment at the same time, but also upgrades while making use of existing analog equipment, or gradual upgrades over multiple plant outages.
