Digital Instrumentation and Controls (I&C) systems have been in use for over three decades in various applications. Fossil power plants and refineries have been using integrated digital I&C systems since the 1980s. Digital I&C systems are widely used in almost all industrial applications in one form or another.

The use of microprocessors and computers is not new in nuclear power plants. Early applications were limited to programmable logic controllers and plant process monitoring computers. In the 1980s, digital technologies were integrated into control systems for various subsystems, starting with the auxiliary systems and then moving to primary systems. By the 1990s, microprocessors were being used for data logging, control, and display for many nonsafety-related functions.

Foreign Nuclear Plants

In Japan, the first fully digitalized I&C system was integrated into the Kashiwazaki-Kariwa Unit 6 advanced boiling-water reactor (ABWR) in 1996. This was followed by Kashiwazaki-Kariwa Unit 7. France, the United Kingdom, Korea, Sweden, and other countries have also implemented digital I&C systems in their nuclear power plants.

Domestic Nuclear Plants

In the United States, digital I&C systems have been used in many applications in nuclear power plants, including feedwater control systems, recirculation control systems, demineralizer control systems, main turbine controls, and many other nonsafety systems. With the NRC approval of the Eagle Series, the Common Qualified Platform (Common Q), Triconex, and the Teleperm XS system for safety-related applications, operating nuclear power plants may consider their use in retrofitting digital I&C systems at their facilities.

All new nuclear power plants are being designed with integrated digital I&C systems as the backbone of protection, controls, alarms, and display and monitoring.

Fuel Cycle Facilities

Several fuel cycle facilities make extensive use of distributed control systems and programmable logic controllers (PLCs) based on digital design technology both in their normal process control systems and safety control systems. An example of the use of digital technology in process control in a fuel cycle facility would be controlling the moisture content of steam used in a process vessel through control of the steam temperature. Digital technology could also be used to perform a safety function as an interlock that prevents filling of a vessel if it is not in the proper location.