A few of the world’s nuclear power plants are described briefly in this section to give the reader an idea of present computer applications These plants were selected because they are completed or soon will be, have some degree of computer control, and have been adequately discussed in meetings or publications. Pertinent data are summarized in Table 8.5. The dates listed are years during which the plant

goes on-line as a power-generating station, in some cases these have been inferred from other planned milestones, such as plant completion and date critical

8-7.1 Douglas Point

The CANDU reactor20 at Douglas Point, Ontario, is probably the earliest planned use of digital-computer control in a nuclear power plant At present the computer directly drives neutron absorber rods to control the reactor flux profile and indirectly adjusts power by providing the set point to the analog moderator level controller

As an assist to higher plant factor, the computer also modifies safety-circuit operation. The safety circuit alone will initiate scram if low coolant flow in any fuel channel is signaled, however, when the computer is operating, it inhibits the trip unless low flow is accompanied by high coolant outlet temperature.

8-7.2 Marviken

The Marviken Nuclear Power Plant,18 a 200-MW(e) station, will have a comprehensive set of sequence programs for start-up, running, shutdown, and refueling These are largely automatic with interspersed stopping points that require a manual command to proceed The control system will also automatically adjust the throttle valves in 32 superheat channels in the reactor core, a difficult procedure because a high-channel temperature requires resetting not only the affected channel valve but also those in several surrounding channels This is a good example of applying computer control where other means are inadequate.

8-7.3 Wylfa

Wylfa,21 a MAGNOX reactor station, is the first in a series of three plants in which computer-based data and display systems have been applied progressively more toward direct control as United Kingdom experience grows Wylfa has automatic turbine run-up

8-7.4 Dungeness “B”

In addition to automatic turbine run up, the Dungeness “B,”22 an advanced gas-cooled reactor station, will have complete start-up, from subcrmcal to power, under com­puter control with manual intervention required if the system encounters abnormal conditions The computer will also control, by rod movement, the ratio of outlet gas temperatures among five reactor zones This is a difficult control problem under all conditions of coolant flow and reactor power level

8-7.5 Hinkley “B”

Except for a different array of inputs and outputs, the Hinkley “B”13 is controlled similarly to the Dungeness “B ” Both stations are examples of the “dual-plant three — computer” configuration discussed m Sec 8-5.

8-7.6 Prototype Fast Reactor

Automatic computer control of reactor flux, coolant outlet temperatures, and steam-generator outlet tempera­tures is being considered for the prototype fast reactor,1 6 a 250-MW(e) sodium-cooled fast reactor facility This is the plant, cited before, in which a detailed economic and technical study resulted in a redundant computer system and a revision of principles to allow plant shutdown on complete control-system failure

8-7.7 Pickering

Nearly all the major reactor variables in the Pickering Nuclear Power Station,23 as in other Canadian plants, will be computer controlled. This includes flux profile, overall reactivity, boiler pressure, and the fueling process

8-7.8 Gentilly

As in the Pickering, most control of the Gentilly Nuclear Power Station2 4 will be by computer Of interest is the reactor’s large positive void coefficient, which will be compensated by moving a set of booster rods according to changes in plant power level Primary-coolant flow valves will also be automatically controlled as a function of power

REFERENCES

1 T J Williams, The Application of University Research to Industrial Process Control, in 22nd Annual ISA Conference, Chicago, 1967, Part 3, Paper No 5 1 ACOS-67, p 3, Instrument Society of America, Pittsburgh, 1967

2 Control Engineering Company, Compilations of Process Control Applications in Control Engineering, May 1962, September 1963, August 1965, September 1966, March 1967, July, 1968

3 M. A Schultz and F C Legler, Application of Digital Computer Techniques to Reactor Operation, in Proceedings of the Third International Conference on the Peaceful Uses of Atomic Energy, Geneva, 1964, Vol 4, pp 321 330, United Nations, New York, 1965

4 M A Schultz, Automatic Digital Computer Control, Sec 4 2, in Small Nuclear Power Plants, USAEC Report COO-284(Vol 2), pp 126 130, Chicago Operations Office, March 1967

5 W C Lipinski, Optimal Digital Computer Control of Nuclear Reactors, USAEC Report ANL-7530, Argonne National Labora tory, January 1969

6 J T Tou, Digital and Sampled Data Control Systems, McGraw Hill Book Company, Inc, New York, 1959

7 W D T Davies, Control Algorithms for DDC Instrum Pract 21 70-77 (January 1967)

8 К L Gimmy, On-Line Computers at the Savannah River Plant in Application of On Line Computers to Nuclear Reactors, Seminar held at Sandefjord Norway, September 1968, pp 727 737, Organization for Economic Cooperation and Development, Pans, 1968

9 A Pearson and C G Lennox, Sensing and Control Instrumenta tion, in The Technology of Nuclear Reactor Safety, Vol 1, Reactor Physics and Control, T J Thompson and J G Beckerley (Eds ), pp 285 416, M I T Press, Cambridge, Mass, 1964

10 J R Howard, Experience in DDC Turbine Start Up, ISA (Instrum Soc Amer) J, 13 61-65 (July 1966)

11 T J Glass Current Trends in Process Computer Software paper presented at Annual ISA Conference, Chicago, 1967, Paper No D2 3 DAHCOD67

12 R G Basten, Impact of Nuclear Reactor Control on the Structure of Computer Systems, in Application of On Line Computers to Nuclear Reactors, Seminar held at Sandefjord, Norway, September 1968, pp 517 533, Organization for Economic Cooperation and Development, Pans, 1968

13 M W Jervis, On Line Computers in Central Electricity Generat ing Board Nuclear Power Stations, in Application of On Line Computers to Nuclear Reactors, Seminar held at Sandefjord, Norway, September 1968, pp 51 78, Organization for Economic Cooperation and Development, Pans 1968

14 Computers in Control, Nucl Lng, 11 618 620 (August 1966)

15 J C Kite, How to Assure Maximum Performance in Redundant Computer Control Systems, paper presented at Annual ISA Conference, Chicago, 1967, Paper No D4 4-DAHCOD-67

16 N T C McAffer The Computer Instrumentation of the Prototype Fast Reactor, in Application of On Line Computers to Nuclear Reactors Seminar held at Sandefjord, Norway, September 1968, pp 351 379, Organization for Economic Cooperation and Development, Paris, 1968

17 Hinkley Point B, Nucl Lng, 12 26-28 (January 1967)

18 J Akesson, Techniques of Computer Application For the Marviken Nuclear Power Plant, in Application of On Line Computers to Nuclear Reactors, Seminar held at Sandefjord, Norway, September 1968, pp. 301-318, Organization for Economic Cooperation and Development, Paris, 1968

19. J. C Spooner, Real Time Operating System for Process Control, paper presented at Annual ISA Conference Chicago 1967 Paper No D1 1 DAHCOD 67

20 E Siddall and J E Smith, Computer Control in the Douglas Point Nuclear Power Station, in Heavy Water Power Reactors Symposium Proceedings, Vienna, 1967, International Atomic Energy Agency, Vienna, 1968 (STI/PUB/163)

21 D Wellbourne, Data Processing Control by a Computer at Wylfa Nuclear Power Station, m Advances in Automatic Control Convention held at Nottingham England, Apr 5-9, 1965, Paper 16, Institute of Mechanical Engineers London

22 A R Cameron, The On-Line Digital Computer System For The Dungeness “B” Nuclear Power Station, in Application of On-Line Computers to Nuclear Reactors, Seminar held at Sandefjord, Norway, September 1968, pp 273 300, Orgamza tion for Economic Cooperation and Development, Pans, 1968

23 J E Smith, D>gital Computer Control System Planned For Pickering Nuclear Station, Elec News Lng, 39-41 (March 1967)

24 W R Whittal and К G Bosomworth, Dual Digital Computer Control System For the GentiUy Nuclear Power Station, 4th International Federation for Information Processing Congress, Edinburgh, Scotland, Aug 5 10, 1968, North-Holland Publish­ing Company, Amsterdam, 1969

BIBLIOGRAPHY

A comprehensive bibliography covering the general field of com­puter control is presented in T J Williams, Computers and Process Control, Ind Lng Chem, 62(2) 28 (February 1970)

Argonne National Laboratory, Liquid Metal Fast Breeder Reactor (LMFBR) Program Plan, Vol 4, Instrumentation and Control, USAEC Report WASH 1104, August 1968 Bullock J В and H P Danforth, The Application of an On Line Digital Computer to the Control System of the High Flux Isotope Reactor (HFIR) in Application of On Line Computers to Nuclear Reactors, Seminar held at Sandefjord, Norway, September 1968 pp 459-478, Organization for Economic Cooperation and Development, Paris, 1968 Demuth, H В, J Bergstein, К H Duerre, and F P Schilling, Digital Control System for the UHTREX Reactor, in Apphca tion of On Line Computers to Nuclear Reactors Seminar held at Sandefjord Norway, September 1968, pp 621 642, Orgamza tion for Economic Cooperation and Development, Pans 1968 Ethenngton, H (Ed) Nuclear Engineering Handbook, McGraw Hill Book Company, Inc, New York, 1958 Freymeyer, P, and H Stein, Automation in the Control of Nuclear Power Stations, Kemtechmk, 11(9/10) 514 (September/

October 1969)

Harrer, J M, Nuclear Reactor Control Engineering, D Van Nostrand Company, Inc, Princeton, N J, 1963 Holland, L К , On Line Computer Experience with Boiling Water Reactors Trans Amer Nucl Soc 9(1) 264 (June 1966)

Moen, H, et al, Computer Control of the Halden Boiling Heavy Water Reactor, in Application of On Line Computers to Nuclear Reactors, Seminar held at Sandefjord, Norway, September 1968, pp 647 667, Organization for Economic Cooperation and Development Pans, 1968

Morin, R, Utilization of Digital Computers tor Starting and Running the EDP 3 Atomic Power Plant, Report AECTR-691, December 1967

Nuclear Reactors Built, Being Built, or Planned in the United States as of December 31, 1968, USAEC Report TID 8200 (19th Rev ), December 1968

Pearson, A Computer Control on Canadian Nuclear Reactors, in Application of On Line Computers to Nuclear Reactors, Seminar held at Sandefjord, Norway, September 1968, pp 123-144 Organization for Economic Cooperation and Develop ment, Pans, 1968

Schultz, M A, Control of Nuclear Reactors and Power Plants 2nd ed McGraw-Hill Book Company, Inc, New York, 1961

Williams, T J, A Manual for Digital Computer Application to Process Control, Purdue University Press, Lafayette, Indiana, 1966

8- 1 INTRODUCTION

The safe operation of nuclear power reactors requires that many of the instrumentation and control systems have a high degree of reliability. One factor in reliability is the integrity of the power source for the instrumentation and control power buses. This chapter provides the designer of instrumentation and control systems with sufficient in­formation to choose the power-source system best suited to his specific application and giving maximum support to the overall system reliability.

8- 1.1 System Requirements

The power sources most commonly used are electrical. Accordingly, this chapter deals mainly with them and only briefly with nonelectrical systems. The common combina­tions of static, rotating, and stored-energy system com­ponents are discussed. Battery-supported static inverter systems, which are among the most frequently used electrical source systems, are emphasized.

The systems discussed differ with respect to their degree of noninterruptibility, i. e., their capability to con­tinue operating under emergency conditions after normal source failure, the quality of their output, and their cost. The designer of instrumentation and control systems must first determine his requirements and establish the relative importance and criticality of each part of the system before choosing the most economical power-source systems to meet his needs. The various systems described offer phase changing, direct-current transformation, line-frequency and line-voltage transformation, isolation, and stabilization. Capability for short-time operation with stored-energy sources and long-time operation with engine-driven energy sources can also be included.

9- 1.2 Design Objectives

To design the power-source system for nuclear-reactor instrumentation and control and to achieve maximum reliability requires, at the outset, a thorough evaluation of the load characteristics. A designer of electronic systems is painfully aware of the risks in having instrumentation and control systems depend on plant auxiliary-power sources.

9-1 Introduction……………………………………………………………… 212

9-1.1 System Requirements…………………………………………. 212

9-1.2 Design Objectives……………………………………………… 212

9-2 Types of Power Supply…………………………………………….. 213

9-2.1 System Similarities……………………………………………. 213

9-2.2 Energy Storage Methods……………………………………… 213

9-3 Requirements for Power Supply……………………………………… 213

9-3.1 General System Categories………………………………….. 213

(a) Interruptible Systems…………………………………. 213

(b) Noninterruptible Systems…………………………….. 213

9-3.2 Load Characteristics and Causes of Trouble. . . 214

9-4 Components of Power-Supply Systems…………………………….. 214

9-4.1 Static Inverters…………………………………………………….. 214

9-4.2 Storage Batteries……………………………………………….. 216

9-4.3 Stored-Energy Eddy-Current Coupling………………….. 217

9-4.4 Engine-Driven Alternators………………………………….. 218

9-4.5 A-C and D-C Drive Motors…………………………………. 218

9-5 Design of Power-Supply System………………………………………. 219

9-5.1 Simple A-C/D-C System……………………………………… 219

9-5.2 Rectifier—Battery System…………………………………… 219

9-5.3 Rectifier—Battery—Static Inverter Systems. . . 219

(a) Basic Continuous-Inverter System………………….. 219

(b) Continuous-Inverter System with Direct

A-C Feed………………………………………………….. 219

(c) Continuous-Inverter System with

Electromechanical Transfer Switch…. 22u

(d) Continuous-Inverter System with High­Speed Transfer Switch 220

(e) Continuous-Inverter System with

Redundant Inverter and Transfer Switch. .221

9-5.4 Generator and Internal-Combustion-

Engine System…………………………………………………………. 222

9-5.5 Synchronous Motor-Generator—Flywheel-

Clutch—Internal-Combustion-Engine Systems…. 222

(a) Nonisolated System…………………………………….. 222

(b) Isolated System…………………………………………. 223

9-5.6 Induction Motor-Generator—Stored-Energy

Eddy-Current-Coupling—Internal-Combustion-

Engine System………………………………………………………… 223

9-5.7 Synchronous Motor-Generator—Stored-Energy

Eddy-Current-Coupling—Internal-Combustion-

Engine System…………………………………………………………… 224

9-5.8 Battery-Supported Motor-Generator Isolated

Systems…………………………………………………………………. 224

(a) Motor-Generator—Motor-Battery System. . 224

(b) Static Rectifier—Motor-Generator—

Battery System…………………………………………… 224

9-6 Conclusions……………………………………………………………….. 224

Bibliography………………………………………………………………….. 225

Complete independence from outside power sources would provide ideal integrity. The best power system for a particular application cannot be designed by just selecting available components to obtain complete power-source independence. The designer must take into account, in his effort to satisfy the overall design objectives economically, such aspects as the allowable outage time of the power source, allowable transfer time between normal and standby power sources, initial cost, maintenance expense, and operating cost The system that provides the desired reliability with the minimum cost is usually based on a compromise between many design considerations

This system (Fig 9.12) consists of a synchronous motor, fed from the utility power system, which drives a synchronous generator, which, in turn, feeds the critical a-c load. Simultaneously, a small induction motor is driving a flywheel at a speed considerably in excess of the syn­chronous generator speed. The flywheel is not coupled to the generator under normal operation since the eddy current coupling between the generator and flywheel is not energized. When an unacceptable excursion in voltage or frequency occurs on the plant auxiliary-power system, the power-source feed is disconnected and the eddy-current coupling is energized, thereby coupling the flywheel to the generator. The stored energy of the flywheel then serves to drive the generator at synchronous speed in the same manner as described for the system shown in Fig 9 11 The present system (Fig 9 12), by excluding the eddy-current coupling from being energized during normal operation, operates at a much greater efficiency than the svstem shown in Fig. 9.11.

addition, a second in-line d-c motor, normally floating on the battery system, is instantaneously available to drive the system if the plant auxiliary-power system fails This system suffers from the ills common to all s) stems with rotating equipment, including increased maintenance and wear, when compared to static systems In addition, the duration of operation after the failure of the utility source is limited by the battery capacity

(b) Static Rectifier—Motor-Generator—Battery Sys­tem. During normal operation of the system (Fig 9 14), utility-line power is rectified and applied to the d c motor that dnves the a-c generator supplying power to the critical a-c load. The rectifier is sized to accommodate any normal d-c load in addition to the power required by the d-c motor and the power needed to maintain the battery at full charge. On failure of the plant auxiliary-power system, the d-c motor is supplied with power from the batteries, thereby maintaining the continuity of the a-c generator

With the exception of improved efficiency, this system has the same characteristics as the system described in Sec 9-5 6, and, in addition, the frequency excursion of the generator output during transfer from normal utility supply to flywheel operation may exceed acceptable limits

9- 5.8 Battery-Supported Motor-Generator Isolated Systems

(a) Motor-Generator—Motor-Battery System In the normal operation of the isolated system (Fig. 9.13), an a-c motor, fed from the plant auxiliary-power system, drives an a-c generator, which, in turn, feeds the critical a-c load. In

prime mover. The length of emergency operation is limited by the capacity of the battery. Adding a backup internal — combustion engine to drive the generator directly would, of course, greatly extend the length of emergency operation.

The base system affords satisfactory operation during short-term transients because of the extremely effective filtering action of the battery and motor—generator com­bination.

9- 6 CONCLUSIONS

The material of this chapter aids in selecting and specifying high-reliability power sources Only the major electrical systems have been discussed because they are the most commonly used in nuclear power reactor plants.

In determining which type of system is best, an important aspect is responsibility. A given system may be designed and specified and the component parts purchased and assembled by the purchaser The purchaser thereby assumes the responsibility for satisfactory system opera­tion.

An alternative procedure, and one that usually guaran­tees satisfactory results, is to specify the required parame­ters of the power source The system supplier then submits a quotation and assumes the responsibility for system operation to meet the specifications This latter procedure is recommended.

BIBLIOGRAPHY

Bleikamp, R P, Load Factors in Selection of Eddy-Current Drives, Elec Mfg„ 63(4) 92-98 (April 1959).

C & D Batteries, Division of Eltra Corporation, Longer Life For Lead Acid Stationary Batteries, Technical Bulletin RS 15810M, November 1, 1964.

Dunsmore, C L, Integrated Emergency Power Supply For Nuclear Plants, Power Eng. 72(8) 39—41, 89 (August 1968).

Everson, H К , Uninterrupted Electric Power Systems Utilizing A DC motor As Emergency Drive IEEE Transactions on Aero space Support pp 1371 — 1384 Institute of Electrical and Electronics Fngineers

Farber, J D„ and D C Griffith, Static Inverter Standby AC Power for Generating Station Controls, IEEE Paper 31PP67 15, Insti tute of Electrical and Electronics Engineers General Electric Company, Static Inverters and SCR Regulated

Battery Chargers, Technical Bulletin GEA 7522b

General Electric Company, Static Uninterruptible Power For Critical Loads, Technical Bulletin GEA 8631 Gould National Batteries, Inc, Gould Invert A Stat DC to AC Static Inverter, Technical Bulletin

Grooms, F H., and P D Wagner, Which Standby Power System Is The Best For You5, Hosp. Management (June 1963)

Hoxie, E. A. Some Discharge Characteristics Of Lead—Acid Batteries, AIEE Paper 54-177, presented at AIEE Winter General Meeting, New York, Jan 18—22, 1954, American In­stitute of Electrical Engineers

Ideal Electric and Manufacturing Company Eddy Current Coupling Variable Speed Drives Bulletin 100 Jackson, S P, Application of Static Inverters In Control And Instrumentation Systems IEEE Transactions on Industrial Electronics and Control Instrumentation, Vol IECI 13, No 1, Institute of Electrical and Electronics Engineers April 1966 Jackson, S P, Standby Power, Instrum, Contr Syst, 39(6) 135 (June 1966)

Jackson, S P, The Use of Static Inverters in the Gas Industry, Gas Mag, 41(12) 48—53 (December 1965)

Mueller, George V, Alternating Current Machines McGraw Hill Book Company, Inc, New York, 1952 Rubenstein, L., Precise Continuous Power, Actual Specif Eng pp 60-66 (August 1967)

Taylor, W H, Reliable Power Packages For Switchgear Tripping Control And Emergency Diesel Engine Starting, AIEE Paper CP 62-484, presented at AIEE Winter General Meeting, New York, January 1962, American Institute of Electrical Engineers

The preceding sections were concerned with the processes in a facility that were placed under computer direction There remains the question of how extensively should the control system cover the full range of operating conditions

If our only worry were to keep a reactor plant going in stable fashion at full power, it would be difficult to justify computer control The task of regulating processes under minor perturbations usually can be done adequately by analog controllers Even operation at different predeter mined power levels can be provided, although m a large plant this begins to reach the practical limit of analog capability An example is automatic power reduction, sometimes called “power setback,” where several combina­tions of out-of limits measurements can automatically cause the plant to go to a selected lower power, thus avoiding the stresses of a full scram and the consequent restart troubles

The greatest need for computer control arises during operation at reduced or changing power levels Changes in power level may be planned, as in start-up or shutdown, or unforeseen, as in recovery from transients and response to equipment failure The superiority of a computer-based system under such conditions is due to one or more of the following

1 There are a large number of interdependent proce­dural steps to be taken that a computer can execute in considerably less time and with a lower probability of erro than with human operators using conventional controls Reactor start up and steam turbine run-up are in this class 1 0 Both are being included in current reactor plant designs

2 The controlled variables are changed at different operating levels One way to start up a reactor is to maintain a fixed and safe period up to about 1% of power, then to raise the level while keeping below a predetermined maximum power rate of rise to avoid damaging thermal stresses, and finally to control at full power with power level as the input to the control program The decision­making ability of the computer can be used to make these changes in control organization at the optimum points in the ascent-to-power routine

3 Control elements, processes, and sensors are non­linear Fixed controller settings can provide good regulation over a limited part of the plant operating range but produce inefficient or unstable behavior at others Again the ability of the computer to make decisions allows it to adjust its

own transfer function automatically to fit changing plant characteristics and to provide nearly optimum control under all conditions

4 Corrective actions often require a faster speed of response than human operators can provide Automatic power reduction is a good example The combination of fast logical analysis of a large amount of data and the ability to take quick remedial action permits the computer system to reduce reactor power or to shut down the plant in a controlled manner and to avoid situations that would cause reactor scrams This results in two very real benefits (1) reducing reactor scrams lessens the chance of damage by thermal and mechanical stresses, thereby reducing mainte­nance and increasing the useful plant lifetime, and (2) lowering power only as far as is necessary allows rapid recovery to full power and raises the plant factor

9- 2.1 System Similarities

Each available power-source system provides a different degree of power continuity and independence, or isolation, from the plant auxiliary-power system In general, each system has a form of stored energy for providing power to the critical bus during an unacceptable frequency or voltage excursion and during the time interval when it becomes necessary to disconnect the normal source of power and transfer to the standby power source Each system has a means of isolating the unacceptable normal power source and initiating the alternate source (if one is provided) before the stored energy of the system is depleted Automatic reconnection to the normal source, after it has returned to a stable condition for a given period, is also a common feature

8- 2.2 Energy Storage Methods

The five major ways to provide stored energy for a standby power system are

1 Pneumatic (stored air or gas) systems

2 Hydraulic accumulation systems

3. In-house or on-site steam-driven turbogenerator systems

4. Inertia, flywheel with and without eddy-current coupling systems

5. Storage-battery-supported systems

The first four systems are commonly used with rotating machinery, and the last is associated with static* systems

The last two methods are electrical in nature and have had the greatest acceptance Each of the last two methods is used to improve the quality of the power normally provided by the plant auxiliary-power source by acting as a filter or buffer When they are combined with a diesel- dnven generator backup, they also provide reliable protec­tion from prolonged power outages Storage-battery systems are normally combined with static battery charging rectifiers and either static inverters or d-c to a-c motor—

•“Static’ as used here means “no moving parts ” generator sets to provide short-time power continuity Static inverters, with and without output transfer switch­ing, have also gained wide acceptance as reliable sources of a-c power for critical loads

R. James Hall, Jerry J Engel, Gordon W. Young, and R. W. Madsen

10- 1 INTRODUCTION

The designers and constructors of the first nuclear power plants generally followed installation practices al­ready established for conventional process and chemical industries Adapting process instrumentation systems to nuclear power plants was reasonably successful However, nuclear radiation systems had no conventional counter­parts During installation and preoperational tests in nuclear power plants, noise problems were found to be common­place, and extensive modifications to the signal, control, power, and ground cables were required before nuclear radiation instrumentation systems could satisfy the estab­lished safety criteria

Since the nuclear power plants being built today involve many different geometric configurations and a number of different basic materials, it is impractical to recommend a standard installation for all plants However, the material presented here should provide engineers m the design and construction fields with a set of installation practices that will enable them to avoid many problems and pitfalls

10- 2 REACTOR INSTRUMENTATION SYSTEMS

9- 2.1 Control Room

The control room in a nuclear power plant has many features in common with fossil-fueled generating stations Many practices developed in fossil-fueled plants are directly applicable to nuclear plants

The control room should be designed and installed so that it can be safely operated and occupied under any external hazard condition, such as fire, smoke, contami nated atmosphere, flood, seismic disturbance, or major electrical fault

An acceptable nuclear power-plant control-room instal­lation requires not only that equipment and components be integrated into a compatible system capable of the neces­sary overall performance but also that the human operator and his relation to this equipment be considered If the man—machine relation is to provide maximum efficiency m operation, human factors must be considered as part of the initial engineering criteria 1 he control console and panel must be arranged so the reactor can be operated in a reliable manner with a minimum number of personnel

Good design and installation practices dictate that all important variables in the plant operation be available for display and control in the station control room Variables associated with reactor and heat transfer control are gener­ally installed on the mam control console Variables associated with the auxiliary equipment, such as the turbine and generator control, electric switchgear control, and several process-instrumentation control systems, are usually installed on the control panel

A representative control-room installation is shown in Fig 10 1 A plan view of this control room is shown in Fig 10 2

9- 2.2 Control Console

The wraparound control console is widely accepted by the nuclear industry The console shown in Fig 10 1 is one example of good installation practices The accessibility to instruments, switches, controls, and terminal boards at the rear of the console is excellent The console is installed on a base structure that provides a step-down passageway behind the terminal boards and termination points at the rear of the control console Access to this passageway is through the rear doors of the console The passageway is wide enough to accommodate important test equipment, such as oscilloscopes

In some nuclear power plant installations the main control console is incorporated into and made an integral part of the vertical control board (see Sec 10-2 3) Accessibility to instruments, switches, and controls is made at the rear of the vertical control board

The following practices, based on observations of control consoles in several nuclear plants and on experience in nuclear-plant maintenance, are recommended

1 Accessibility to the rear of the console must be provided for maintenance and test

2 All field cabling coming into the control console and cabinets must be brought through a suitable dust seal, such as a penetration sealed by a compound This provision will help to maintain the control room at a slightly higher pressure than ambient to prevent such hazards as fire, smoke, and noxious fumes from spreading into the control center

3 Access must be provided to all components and electrical connections to facilitate maintenance (see also Sec 10 4)

The time-shared nature of a process computer system makes it capable of doing nonessential off-line tasks at the same time that it is controlling the plant The central processor idle time could be used to compile and run FORTRAN calculating routines, assemble new subroutines, or modify and expand the process control programs 1 1 However outweighing the benefit of greater machine utilization are the following drawbacks

1 The operating speed of a nuclear-plant control system does not permit interchanging whole programs between core and drum (or disk), so the core memory must be larger

2 Greater keyboard—printer capacity is needed

3 A much more complex monitor is required

4 There is a finite probability that the time-shared systems software will derail the control program, although this probability can be made small through a computer memory-protect feature.

Taking all these into consideration, with nuclear safety to emphasize the last item, power-reactor control engineers have not included on-line program preparation as a system function An exception, discussed in Sec 8-5 4, is a configuration of redundant central processors where one is on standby and may be used by a programmer until interrupted to take over the control task 1 2

8- 4.6 Typical Applications

Examples of computer applications to specific power — reactor functions are given in the chapters on instrumenta­tion systems in boiling water reactors (see Vol 2, Chap 16, Sec 16-9), sodium-cooled reactors (see Vol 2, Chap 17, Sec 17-5 5), and gas-cooled reactors (see Vol 2, Chap 18, Sec 18-6 3)

8- 3.1 General System Categories

Instrumentation and control power systems may be categorized as either interruptible or nomnterruptible.

(a) Interruptible Systems. Interruptible systems are those m which power is obtained directly from the plant auxiliary-power system through suitable filters and regulat­ing equipment, if they are required to improve the power quality. An interruption of plant auxiliary power results in total loss of instrumentation power This type of system is applicable only where the instrumentation and control loads are noncntical, i. e., absolute continuity of operation is not essential. Usually the total interruption time is a maximum of approximately 15 sec, ie., the time in which the plant standby auxiliary power source, several diesel — engine-dnven generators, reestablishes power to the essential auxiliary buses

(b) Noninterruptible Systems. Nomnterruptible systems are those in which any interruption of power results in loss in continuity of operation or m erroneous operation of critical instrumentation and control loads Since nomnterruptible power systems are the type most commonly required for nuclear-reactor instrumentation and control applications, the remaining sections of this chapter concentrate on power-source systems that are noninter­ruptible for a discrete length of time after a plant auxiliary-power failure.

There are two categories of nomnterruptible power systems, nonisolated and isolated

Nonisolated systems are those in which plant auxiliary power is imposed directly on the essential auxiliary-power buses Normally the nomnterruptible power supply is also fed from these essential power buses and is storing up potential energy. If a plant auxiliary system fails or if there is a severe transient, the nomnterruptible power supply releases the stored energy to the critical bus, thus affording a short-time carry-over of stable power

The more commonly used type of noninterruptible power supply is the isolated system This differs from the nonisolated system in that the instrumentation power buses do not receive power directly from the plant auxiliary power system but rather through the nomnterruptible power supply. The nomnterruptible isolated power supply thus acts as a filter or buffer separating the instrumentation power buses from the plant auxiliary-power system and any transients that appear on that system

The control panel is referred to as the “control board” or “vertical board” in the electric utility industry A variety of control instruments, recorders, indicators, meters, dials, and knobs are installed on the control panels The more familiar instrument systems include (1) switchgear and substation control, (2) turbine and generator control,

(3) critical-temperature measuring recorders and scanners,

(4) process instruments for controlling and monitoring critical pumps and valves in the auxiliary heat transfer loops, (5) emergency shutdown and monitoring for water reactors, (6) water treatment, and (7) annunciator alarm windows for all control panels involved The neutron­monitoring instrumentation cabinets and drawers and the radiation-monitoring system may be installed as part of the control panel or in separate cabinets

The depth of a control panel should be no more than required for easy access to all terminals and components at the rear Avoid stacking instruments and conduit boxes behind panel board instruments at the rear of the control panels It limits access to terminals and components at the rear of the panels and can adversely affect the safety of plant operation

Field cables entering the control panels either from floor conduits or from overhead trays should be bundled

“ Ml И. P » }} щ Щ i,
Fig. 10.1—Control room of the San Onofre nuclear generating station.
MATRIX PARTIAL TRIP ANNUNCIATOR
FIRST-OUT AND PRE­TRIP ANNUNCIATOR	REACTOR PLANT ANNUNCIATOR N0.1
PERMISSIVE DISPLAY
AUXILIARY COOLING WATER CONTROLS
PROCESS CONTROLS PROCESS RECORDERS
■ STEAM-GENERATOR CONTROLS READOUT RECORDS FEEDWATER CONTROLS MAKE-UP WATER CONTROLS
MAIN CONTROL, CONSOLE
-PRIMARY LOOP CONTROLS READOUT RECORD	-NUCLEAR INST. READOUT CONTROL-ROD CONTROLS READOUT RECORDER
OPERATOR’S LOG DESK AND STATION COMMUNICATION CENTER
-TURBINE-GENERATOR CONTROLS READOUT RECORD
u- <

and installed in a manner that will not inhibit access to any instruments, components, controls, or termination points at the rear of the control pane! The installation of racks and cabinets is discussed in Sec 10-3

Graphic panel installations already generally accepted for control in fossil-fueled power plants are being used in nuclear power plants, particularly for generator output bus, switch gear, substations, and heat-transfer systems Opin ions differ as to the effectiveness of graphic panels since the plant operator gets accustomed to the control knobs, lights, indicators, etc (see Sec 10-6) However, a survey of operating personnel in several generating plants revealed a decisive preference for graphic panels m the central control room

9- 2.4 Nuclear-Instrument Systems

Slide out drawers containing electronic circuits which are housed in some modular arrangement have been accepted as a standard for nuclear industry Either a Nuclear Instrument Module System (NIMS) bin configura­tion is used or modules are removed from the top of the chassis The installation and interfacing of nuclear mstru ments with the control and signal cabling coming into the cabinet must be done properh

Very serious operating problems will affect the perfor­mance of the nuclear instrument channels if there is improper installation and bundling of critical coaxial, triaxial, and multiconductor cables Cables that are improp­erly installed frequent!) break otf after they have been flexed a few times, causing open circuits Adherence to the following practices will reduce this problem

1 Avoid supporting a cable, wire, or bundle of wires by the terminal point Good engineering practice provides a solid support fastened to the cable, wire, or bundle such that there is no stress on the terminal Support as much of the cable length as possible bv such mechanical means as cable retractors and springs

2 Avoid using a single-point support Distribute the support points over as wide an area as possible

3 Mount the cable, wire, or bundle so that kinks do not develop Use mechanical stiffening, such as nlon spiral wrap, wherever possible to prevent sharp bends

10- 2.5 Plant-Protection-System Cabinets

Cabinets for the plant protection system contain relays, solid state devices, and other components that make up the logic circuits of the plant protection system The plant protection system should be totally enclosed, either the cabinets themselves or the area in which open cabinets are located

The equipment should be designed so that anv compo­nent can be replaced or repaired without disturbing anv other component Relays and other remotely operated equipment should be accessible for authorized maintenance and troubleshooting and protected against unauthorized access Each component should be clearly marked to prevent a mistake m identification

The cabinet terminal blocks, used to interface the field wiring to the cabinet wiring, should be accessible to the incoming cables as well as to the internal wiring The wiring on the terminal block should be arranged so that the internal wiring is terminated on one side of the terminal block and the field wiring on the other side

Terminal blocks that do not contain field wires may utilize both sides of the terminal block for internal wiring, particularly where it is convenient to install a series of shorting bars In installations where more than one row of terminal blocks is used, the internal wiring should be terminated on the terminals facing a common space between the terminal blocks, thereby leaving a space common to two rows of terminal blocks for the incoming cable terminations

All terminal blocks installed in the plant-protection — system cabinets should be clearly identified by both block and terminal point

The relative importance of the steps in control system design and the order in which they should be taken depend
on the kind and size of the facility, the project components to which the design tasks are assigned, and the time and money constraints imposed No matter what the design procedure, experience has shown the importance of formu­lating and documenting certain design procedures A schedule and a set of rules must be established early in the project, even if they will be changed many times later

The design of a computer-based data-acquisition system or a computer-based control system differs in many ways from that of their analog counterparts The main reason for these differences is that a large part of the system design resides jn the computer programs This fact goes a long way toward explaining why the schedule, vendor responsibility, costing, and specification are so unlike those for analog equipment 1 3

8- 5.1 Schedule

One aspect of the difference between the two systems is apparent from examination of the control-system part of a

CONTROL EQUIPMENT Preliminary design Develop specification Bid review Manufacture

Checkout (acceptance tests)

COMPUTER PROGRAMS Develop specification Design structure Programming training Coding Debugging

Checkout (programs and process) project schedule A typical schedule (Fig 8 5) is developed by taking the target date for reactor start-up as the completion time for the control system The previous 12 to 18 months are then reserved for the major programming effort, which is on-site program development and debugging after equipment delivery Coding starts as soon as the computer model is chosen and finishes when the programs have been tried out on the computer after it has been installed in the plant Still working backward in time, a year or two is allowed for equipment manufacture and check­out The length of this period depends on the complexity of the system and how much of nonstandard hardware is to be put together by the supplier Finally, a few months are added for vendor selection and contract negotiation and a few more for writing the specification. At this point the control engineer finds that he is already behind schedule or, at best, that he will reach the specification deadline having
dangerously little information about the processes that his system is going to control

Then begins the task of shortening the various segments of the chart to produce a properly timed, but realistic, set of goals To be done right, this job requires familiarity and experience with both computer systems and reactor projects Factors that must be considered are

1 The minimum amount of plant design data needed to develop a sound specification

2 The extra control-system capacity that should be specified as a contingency against further plant design changes

3 The anticipated delays because of prevailing procure­ment policies

4 The probable system suppliers and their reputations for making accurate delivery-schedule estimates

5 The available programming personnel

6 The likelihood of a postponement of the plant start up date and the estimated number of months exten­sion

These and many other factors influence the control — system schedule, which becomes a firm guideline for acquiring, programming, and installing the equipment It will, of course, be modified from time to time as the project progresses toward completion