Things to Consider When Upgrading a Non-Power Reactor to a Digital I&C System

Non-Power Reactor (NPR) licensees 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. In Generic Letter GL 95-02, the NRC recognized that the design characteristics specific to the new digital electronics could result in failure modes and system malfunctions that either were not considered during the initial plant design or not evaluated in sufficient detail in the safety analysis report. These concerns include potential common mode failures. A conversion from analog to digital I&C systems in NPRs solves some problems while potentially introducing others. Good design, engineering, review, and testing can identify and minimize these risks.