The Mitsubishi Group and Japanese PWR utilities have been engaged in a continual process of main control board design improvement. Advanced main control boards with fully digital instrumentation and touch operation technology have been adopted in newly constructed plants. Moreover, instrumentation and control systems have been fully digitalized and applied not only to non-safety systems but to safety systems as well. Such a system in general is referred to as a fully digital system. From this time forward, the application of this fully digital system will become mainstream with the modernization of existing plants. Yet, unlike newly constructed plants, restrictions unique to existing plants will need to be taken into consideration. In the construction of Ikata Units 1 and 2 of Shikoku electric power co., measures such as those described below were implemented so as to achieve standardization with future construction in mind: (1) A thorough interface check was conducted to ensure compatibility with sections outside the scope of modernization. Additionally, to minimize the affect modernization had on the operating system, the system was verified by operators and verification results were reflected in the board layout, system specifications, and the like. (2) Due to limited space for board installation, a plan was devised for housing a processor and determining the remote input/output board location. (3) Onsite tests was minimized in order to complete construction within a short period of time, i.e., within the regularly scheduled inspection period, and the degree of completion of the product was enhanced prior to shipment by a full combination test conducted at the plant. In addition, the local construction period was shortened by devising a plan for installing the board and conducting interface tests during the previous regularly scheduled inspection and the current regularly scheduled inspection.

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