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The basic requirements of control and instrumentation (C & I) for large nuclear power stations are reviewed with special reference to the advanced gas-cooled reactor (AGR) and the pressurised water reactor (PWR), emphasising current developments and trends rather than established techniques. The extensive instrumentation, now provided for condition monitoring, particularly of the chemistry of both primary circuit coolant and the secondary steam and water circuits, is reviewed, and the way some of this instrumentation provides indication of failure of boiler tubes and fuel element cladding in AGRs is described. The power station is controlled automatically by a series of closed-loop controllers, and the current trend is discussed of employing direct digital control with redundancy, when it is justified to meet reliability requirements. However, the need for an effective operator interface is regarded as most important, and the current increased concern about ergonomics is identified, particularly in the design of the main control room, with a strong emphasis on formalised design procedures and reviews of existing designs. The increased use of computer-based techniques for control, protection, interlocks, alarm handling and display and data processing is discussed with special refer-ence to the use of colour visual-display units for data and alarm display. The special problems of high integrity applications, with the need for special design and validation of software, and the basic components of computer systems are described, and the current trend towards distributed systems and high-level user-orientated computer-programming languages is identified. Reliability aspects of C & I systems are discussed, including estimation, correlation with field experience and consideration of common mode effects. The need for evaluation and type testing and its cost are discussed and the results of such testing are reported. The overall structure of national and internati- nal C & I standards is described. The organisation and management of a C & I design group is discussed, and the requirements for a systems approach are identified with the use of a matrix structure in a multiproject environment. The rapid obsolescence of modern electronic equipment is discussed and the need for total life cycle support considerations to be incorporated in the design of both hardware and software is identified. An indication is given of current trends in instrumentation, computers and the improvement of operator interface systems.