Plant Maintenance and Improvement Experiences for Control System in UCN 5 and 6

The Plant Control System (PCS) in Korean Standard Nuclear Power Plant (KSNP) is designed to perform data acquisition and transfer function via communication data links to control most of the field components such as pumps, fans, valves, dampers and circuit breakers. The PCS installed at UCN 5 and 6 for both safety related and non -safety related functions is microprocessor based system supplied by HF Controls. Safety related functions are provided by redundant trains of microprocessor based single loop controllers with direct connections to the field input/output instruments but non-safety related functions utilize a similar construction with the input/output boards to be remotely located in cabinet arrangements near the field components. Whatever the functions, the signals to control and monitor field devices are processed through communication master (CM), HFC distributed control system, which uses Multibus I back-plane design to accommodate the requirement of multiple processors. The complex programmable logic device (CPLD) mounted on the A233 back-plane of the CM controls the processors for an adequate access to the bus so that 16 microprocessor based circuitries acting as bus masters share the public memory properly through the common bus. The bus occupation of each processor should not affect overall system response time to keep appropriate system performance. This paper discusses the comparison evaluation between the difference priority techniques and hardware change on A233 back-plane to improve the communication methods, etc., as to the bus arbitration schemes of communication master(CM) applied to UCN site based on the waveform data acquired from A233 CPLD and HFC bus design specification. (authors)