Signal interfacing between systems and cabinets for a phased I&C safety systems upgrade in nuclear power plants

► We build the methodology for I&C system upgrade in nuclear power plants. ► We describe the interface requirements reflecting a phase upgrade. ► Interface requirements we suggest are system configuration, signal interface, and cabinet configuration. This paper presents a standpoint of signal interface for a phased upgrade of instrumentation and control (I&C) systems in a pressurized water reactor (PWR) type nuclear power plant (NPP) in Korea. YongGwang nuclear (YGN) power plant units 3 and 4, which was constructed as a basis model for an optimized power reactor 1000 (OPR1000), is selected as a demonstration model for the presentation. A methodology for building interface requirements is suggested for a phased I&C systems upgrade, maintaining the same functions as those of existing systems, improving functions without violating the compliance requirements, and establishing a safe and economical upgrade schedule. For this, signal interfaces, from the standpoint of safety systems, between I&C cabinets in auxiliary electrical equipment rooms (EER) A and B and the main control room (MCR), the signal interface between the cabinet and the main control board (MCB), and the signal interface between the cabinet and the remote shutdown panel (RSP) are described. This paper focuses on the description of the following interface requirements, reflecting the phased upgrade strategies: system configuration, signal interface, and cabinet configuration. The suggested phased upgrade strategies include the following: non-safety I&C systems should be upgraded in phase 1, safety I&C systems should be upgraded in phase 2, and the MCR should be upgraded in phase 3. The findings presented in the paper can be reliably used to understand upgrade of I&C systems and to implement I&C systems for phased upgrades based on digital technologies.