Insights gained for updating an analog I&C system to a digital system

Licensees at both Nuclear Power Plants (NPPs) and Non-Power Reactors (NPRs) are increasing their use of state-of-the-art digital technology in instrumentation and control (I&C) systems because digital systems offer improved reactor control, information processing, and information storage over analog. Digital I&C systems can range from experimental systems for reactor control research (at NPRs), to measurement and display systems, to complete reactor console replacements. Because of the increasing difficulty in finding spare parts for their original analog I&C systems, many licensees have begun or have plans to upgrade, refurbish, or replace their old analog I&C systems with digital systems. The perception is that upgrading to a digital I&C system will solve all of a facility's obsolescence problems. However, licensees need to be aware of several issues associated with upgrading to a digital system including obsolescence of the digital system (hardware and software) because of the short product life cycle and the associated cost to acquire, store, and maintain a long-term supply of spare parts. Configuration management and cyber security are also vitally important for any upgrade. Further, it must be recognized that the introduction of software and microprocessors could create new failure mechanisms, such as software errors and increased susceptibility to electromagnetic interference. In fact, experience has shown that these failure mechanisms may cause the reactor to malfunction in a way not previously considered. Thus, a conversion from analog to digital I&C systems solves some problems while potentially introducing others. Recognition of the additional risks coupled with good design, engineering, review, and testing can identify and minimize these risks.