14.25. The Three Mile Island accident focused attention on the short­comings of most nuclear power plant control rooms existing at that time since operator response during the accident was complicated by confusing displays, many alarms, and an “overload” of information. Diagnosis of the problems during the stress of the accident was difficult. As a result, practically all control rooms were upgraded to meet new NRC require­ments. Human factors engineering, which is concerned with the interface between people and machines, was recognized as an essential contribution to control room design.

14.26. Control room designs for new nuclear power plants have been developed with important features that we will examine. Much attention has been given to providing the operators with an easily understood struc­tured information display arranged in order of importance, taking advan­tage of extensive computer modeling of plant systems. Expert system and neural network features are used in some systems to provide guidance for remedial actions [3].

14.27. The primary control room objective is to help the operator make the decisions that are necessary, particularly under unexpected circum­stances. To accomplish this, designers have made the most important plant safety and power production information readily apparent on fixed indi­cators, while reducing the number of distracting displays. Less vital infor­mation is made available by a data processing system on color graphic and other video displays. A third level of information is provided on cathode ray tube (CRT) monitors by calling up suitable “pages.” Similarly, alarms are categorized by priorities so that operators are alerted to problems but not overwhelmed with many signals. A “safety panel” informs the operator of the status of the plant during an accident with data processed so that guidance to corrective action is provided. Feedback indicates the effect of such actions.

14.28. Another new feature is a large screen, visible throughout the control room, which provides a graphical color display of the status of the plant and critical functions. This display overview links the vital fixed indicator information with that provided by CRT “pages.” Past major dependency on such CRT access to a great deal of information diminished the operator’s “feel” of the plant condition. Thus, the large display aids coordination and diagnostics. The development of an optimum balance between the various informational and operating tools has required much experimentation using computer-driven plant simulators.

14.29. A typical advanced design control room layout is shown in Fig. 14.2. The operation of major plant functions, such as the core, primary coolant system, and turbine generator, is centered at the master control console (MCC). Other panels serve the safety and auxiliary systems. The MCC is engineered using anthropometric standards for a seated operator

A. Master Control Console

B. Integrated Process Status Overview

C. Auxiliary System Panels

D. Safety System Panels

E. Control Room Supervisor Area

F. Technical Support Center G> Shift Supervisor Office

H. Assistant Operator Work Stations Computer Room

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as shown in Fig. 14.3. Anthropometry deals with the study of human body measurements.

14.30. All new control rooms use digital multiplexing for signal trans­mission. In multiplexing, many different signals are sent over the same wire using different frequencies. Individual sensors are wired to remote terminals where they are sequentially sampled for transmission to the control room area, where the signals are separated and distributed to information­processing equipment. In this way, it is possible to save hundreds of miles of hardwiring.