Garth Driver and Robert E. Mahan

8- 1 INTRODUCTION

The meaning of “automatic control” has changed over the years along with the advance of control technology, the change being mainly one of scope At one time describing a servomechanism, the term was broadened to include feed­back control of a single process parameter, now it usually denotes the untended operation of complex processes or entire plants The word “automation’ was coined to indicate the elimination of the actions and decisions of human operators, it will be applied in this chapter to the internal control of nuclear reactor facilities However, just as advances in automatic control were expansions of scope based on previous technology, we may expect that automa­tion will soon be taken to imply optimum operation under changing external influences, such as product markets and raw materials costs

The instrument engineer has recently been given the chance to begin applying several decades of theory to the control of real industrial processes 1 The means were provided by those digital computer manufacturers who designed or modified their equipment for on-line data handling and control and who developed the beginnings of process program systems Because of the important part computers play in automation, this chapter will deal mainly with the special problems that arise in the design, procure­ment and application of digital computer control systems

The past growth of the field of computer control has shown an exponential trend that is typical of a newly introduced technology 2 The increase may eventually be expected to slow down to more of a linear rise as the demand stabilizes, however, it is likely that the limiting influence will not be the usual market saturation but rather the lack of a sufficient number of knowledgeable applica­tions engineers

The history of computers in control shows an early and continuing preponderance in the petroleum and other chemical industries with applications in electric-power and metals production running not far behind 3 On the other hand, computer control of nuclear facilities is among the

CHAPTER CONTENTS

8 1 Introduction 192

8 2 System Comparisons 193

8-2 1 Analog Control Systems 193

8 2 2 Hybrid Control Systems 194

8-2 3 Digital Control Systems 194

8-3 Degree of Automation 194

8-3 1 Operator Control 195

8-3 2 Monitored Operator Control 195

8 3 3 Operator Guidance 195

8-3 4 Automatic Control 195

8 4 Scope of Automation 195

8-4 1 Conventional Processes 196

8 4 2 Nuclear Processes 196

8-4 3 Auxiliary Processes 196

8-4 4 Start Up and Shutdown 196

8 4 5 Nonprocess Functions 197

8-4 6 Typical Applications 197

8-5 System Design 197

8-5 1 Schedule 197

8-5 2 Preliminary Design 198

8-5 3 Program Description 198

8-5 4 Redundancy 199

8-5 5 Cost Estimates 200

8-6 System Specification 201

8-6 1 Introductory Sections 201

8-6 2 Central Processor 201

8-6 3 Process Input/Output 203

8-6 4 Standard Peripherals 205

8-6 5 Software 207

8-6 6 Environmental and Miscellaneous

Characteristics. 208

8 6 7 Other Sections of the Specification 209

(a) Acceptance Tests. … . . 209

(b) Installation. . . . 209

(c) Training…………………… . 209

(d) Appendixes. … 209

8-7 Current Plant Designs 209

8-7 1 Douglas Point 210

8 7 2 Marviken 210

8-7 3 Wylfa 210

8-7 4 Dungeness “B” 210

8-7 5 Hinkley “B” 210

8-7 6 Prototype Fast Reactor 210

8-7.7 Pickering 210

8-7 8 Gentilly 210

References.. . ..210

Bibliography. . . . . . 211

Fig. 8.1—Analog feedback control system

Fig. 8.2—Analog automatic control system

least developed of the industrial areas, a state of affairs due largely to the plant builders’ and the operators’ uneasiness over acceptance by licensing authorities 4 Once this barrier has been surmounted, we expect nuclear-plant applications to catch up quickly with the rest of industry Moreover, the combination of an expanding competitive nuclear power business, the unusually thorough mathematical representa­tions of nuclear reactors the continuing improvements in computer speed and reliability, and the ability of the computer to solve complex problems affords an un­precedented opportunity for the engineer to apply advanced control methods 5

Control systems can be described in terms of the extent to which they provide automatic plant operation and the kind of equipment used to do it First, a system type may be classed by whether its primary implementation method is analog, digital, or a combination of both. This classifica­tion provides an indication of automation since it implies certain automation capabilities. A second classification concerns the degree of automatic control provided, the criterion being how completely the equipment replaces the human operator’s decisions and actions Third, the system can be described according to its scope, і e, the proportion of the total plant that is under automatic control These three categories will be discussed further in the following section

An underlying objective of automation is improved economics of plant operation, and the anticipated amount of improvement is the measure of the justification for control-system cost This objective will be achieved in different ways depending on the mission of the facility. A power-producing plant with proven components needs a
redundant system with moderate data handling to provide maximum operating continuity, whereas a prototype re­quires less emphasis on high plant factor and more on data acquisition and analysis The effect of facility mission on control-system design will be treated later in some detail because of its heavy influence on system size and cost