A Control Rod Control System (CRCS) is one of the most important pieces of equipment in a nuclear power plant because it controls the nuclear reaction by moving the Control Rod Drive Mechanism (CRDM) in the reactor with speed and direction signals from the Reactor Regulating System (RRS). This paper introduces a CRCS with full-duplex configuration and a Local Operator Module (LOM) computer to enhance reliability in comparison to existing simplex systems. The duplex configuration, LOM program, and maintenance test program of the CRCS are explained in detail. This duplex system can perform a failsafe changeover in only a few milliseconds, which results in ‘bumpless’ CRDM coil current control. In particular, because all the control cards are hot-swappable and power converter modules are drawer type, the operator can replace a malfunctioning module without a system shutdown. For ease of operation, the CRCS has its own panel computer called Local Operator Module (LOM) which has a monitoring program installed. The LOM shows all the CRCS operating information such as urgent/non-urgent alarm status, controller operation status, CRDM coil voltage/current, data logs and detailed event alarms. In the CRCS power cabinet, there is an extra panel for easy and simple module maintenance. If the operator suspects that any module of a power cabinet such as a power control card or a power converter module is abnormal, he has only to place the module in the maintenance panel and run the test program to ascertain the module’s sanity. The operator also can utilize the maintenance panel for spare module testing before the spare module is installed in the system and thus avoid installing a defective module.

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