KEY DESIGN CHALLENGES IN NEXT GENERATION INSTRUMENTATION CONTROL (IC) SYSTEMS FOR SMALL MODULAR REACTOR NUCLEAR POWER PLANTS

摘要

Small modular reactors (SMRs) are a new offering in the landscape of commercial nuclear power generation. Unlike the larger conventional units, these small reactors, with nameplate capacities of 300 megawatts (electric) or less, offer more flexible economic options for utilities, allowing incremental additions to a site's power generation capacity with similar incremental capital outlays. Their smaller reactor cores are more amenable to inherently safe design features that allow for the quality and production cost improvements associated with factory-built, rather than site-built, components. Further reduction in initial capital investment and long-term operational costs is possible by sharing resources and systems among multiple reactor units located in the same plant. These traits and some of their closely related plant characteristics, however, present special engineering challenges in the design of the instrumentation and control (I&C) system. Utilization of a single command center to control and monitor multiple reactors allows resource optimization. This approach, while maintaining a cap on operating costs by making the most of personnel resources, demands attention to human factors in the man/machine interfaces to ensure safe and efficient plant operation. Sharing functionality of costly control equipment, such as balance-of-plant (BOP) equipment between reactors that are possibly in completely different operating modes, places unusual constraints on the data network architecture. This includes communication segment partitioning, interdependency, and loading to ensure that equipment failure conditions can still be properly detected and isolated. Additionally, the impact on reactor safety systems requires careful analysis and understanding. The economy of reusable software and hardware components, such as similar sensors and control algorithms for different subsystem controls or independent redundant channels, introduces potential issues of common cause failures. The introduction of a modern digital communication infrastructure greatly enhances the controllability and maintainability of a nuclear power plant, but it raises the concern of vulnerability to a cyber attack. This paper highlights some of the architectural design approaches related to cost and functional goals of the SMR plant control system and the design strategies necessary to meet the safety and security requirements of the U.S. Nuclear Regulatory Commission (NRC). These results stem from a methodology, based on rigorous systems engineering principles, aimed at balancing the often conflicting needs of an I&C system in a highly-integrated multi-unit plant. Various digital communication technologies are examined for potential deployment in the integration of process control systems, protective functions, and security features of the plant. Monitoring and detection capabilities, required to identify and isolate equipment faults, are examined in their role of preventing cascade failures that may come about as a result of resource sharing. It will further elaborate on digital communications techniques that enable the plant operators to manage, control, and distribute data from a central station without jeopardizing the overall plant reliability and operational safety. The ultimate objective is to describe an I&C system that optimizes plant safety and reliability performance while minimizing the potential negative effects of plant resource sharing.