After the program description and the equipment configuration have been developed, the control engineer has enough information to make a preliminary estimate of system cost He compares the conceptual computer system with a conventional analog layout designed to perform the same basic tasks, which shows whether or not the computer control system is economically acceptable The analog equipment will include panels, panel meters, data loggers, strip-chart recorders, alarm annunciators, and controllers Some controllers must be capable of three-mode, feed­forward, and cascade operation. The systems should have equivalent orders of reliability and redundancy.

In all likelihood the computer control hardware re­quired for a reactor power plant will have a lower cost estimate than the analog configuration but will have a higher estimate when the cost of computer programming is included (see Table 8 3) If so, the decision to use a computer system has to be justified on the basis of services beyond those which analog systems can provide The values of such advantages are difficult to assess, they depend on such things as future savings in plant operating cost, benefits in case of a plant accident of low probability, and capability of readily accommodating later plant modifica­tion. Examples of some advantages are

1. The computer can lessen the time and effort applied to system installation and checkout For instance, several hundred sensors and cables can be connected and tested all at once by using a short computer program to detect and print out faulty channels Such procedures substantially lower installation time and cost compared with the standard method of “ringing out" each signal path by hand

2. The control-room staff can possibly be reduced because of greater efficiency in data acquisition and display Considering the cost of an operator over the lifetime of the plant (diminished by the initial cost of training personnel in the capability, programming language, and structure of the computer-based system), this factor can tip the scales in favor of a computer system Large offsetting increases in other activities usually are not expected, for example, the number of maintenance person­nel should be abouf the same with either kind of hardware, although they will generally be more highly paid for maintaining computer hardware.

3. At some time during its life, the plant will undergo changes in components, operating mode, or power level. The cost of altering the instrument and control system to provide for such changes will vary greatly but will be less with a computer system The cost of adapting to plant modification is hard to forecast except when such action is planned from the beginning. The latter is illustrated by a full-scale prototype power plant that is currently under construction.1 8 At start up and during initial testing, the plant will run with saturated steam, later to be changed to superheated steam to produce full-design electric power. It is estimated that the changeover will be done in a few hours by loading new computer programs, m contrast to a many-month-long job of altering conventional analog equip­ment.

4 The ability to format and output both transitory and permanent data in report form is an asset These data include postincident data, fuel exposure and inventory, and management reports on plant operation.

5. Reactivity balance, control-rod calibration, reactivity coefficient, and other complex on-line calculations can materially aid in efforts to achieve optimum reactor operation.

After all factors such as the above are taken into account and given conservative cost values, the total is incorporated into the initial system cost for comparison against an analog configuration.

The reader is cautioned that the figures in Table 8.3 are composite and illustrative. The cost ratios of the separate items will differ greatly for the various types of reactors and different plant operating modes