BS 6078:1981 download free.Guide to the Application of digital computers to nuclear reactor instrumentation and control.
The use of process computers with nuclear reactor units has become general. While logging remains the basic function of many computer systems, widespread use is made of computers as a means of enhancing conventional instrumentation and of obtaining information not otherwise available. The assignment of tasks vital to plant operation to computer systems requires careful consideration of the factors affecting availability and reliability, when determining the system configuration.
1 Scope and object
This report covers the principles which should be followed in the use of digital computers for alarm, instrumentation, record, control and equipment protection purposes on nuclear reactor units. This report is not a document on design but a guide to the application of digital computer systems.
The application of digital computers to reactor protection is under rapid development at the time of writing and is not included in this edition of the report. The application of distributed digital processing may require additional recommendations to those given in this report.
This report applies to all on-line applications of digital process computer systems to nuclear reactors and to off-line applications immediately associated with the on-line system, such as would normally use the same equipment. The recommendations are based on recognized practice in the process computer field and are functional in nature. These recommendations are not intended to affect the obligations that a supplier of equipment, services or programmes may have for satisfactory performance in any specific application. General recommendations are given for the application of such systems, for the equipment and programmes and for performance and maintenance.
2 Definitions
For the definitions of general terms used in this report, reference should be made to IEC Publication 50, International Electrotechnical Vocabulary (T.E.V.). The following definitions are applicable for the purpose of this publication. A meaning consistent with current use is given, although in some cases no generally agreed definition exists and divergent use is made of a term in different countries.
digital computer system, computer system an equipment system of computers, storage units, input/output units, computer programmes, but not including the measurement transducers or plant actuators
3 Application classes
The tasks assigned to the digital computer system are grouped into four application classes related to plant operational requirements. Consequently, these four classes have varying requirements for availability, redundancy and reliability of the associated computer system, which are discussed in Clause 6.
Class 1
Systems dedicated to performing essential functions for reactor protection (not included in this report). Class 2
Systems performing essential functions for the reactor operation and availability. Significant reactor operation is not possible without continuous availability of the essential data, alarm, control or equipment protection functions of the computer system.
Class 3
Data, alarm, control or equipment aids to operating staff which enhance the plant operation. A failure of the system may result in a degradation of overall plant performance, or may lead to a loss or reduction of reactor operational flexibility within a period of days.
Class 4
Data logging functions used for plant operational recording and as an aid to conventional instrument and alarms. Normally, the signals involved can be checked by other means. Computer failure does not lead to a significant degradation of plant performance.
4 Determination of application class
Where a plant operational function is to be performed by a computer system, the application class shall be determined, in order to determine the redundancy and reliability of equipment needed. This can be done by considering the consequences of operation on short-term or long-term loss of that function.
Where a plant operational function is considered as a possible computer task, the computer application class that is thereby required shall be considered carefully. This consideration should take account of alternative or standby equipment needed, together with economic, technical and safety factors.
Consideration of the information which the different operational, maintenance and managerial staff require will also be a factor in determining the application class.
7 General factors
7.1 System functions
A computer system may provide control and information functions for the plant operators. These functions and the display units, printers and controls over the computer system operations should be fully integrated into the control room design and plant operational concepts.
7.2 Computer system equipment
The design of the computer system equipment should take account of the different types of station instrumentation and alarm signals. It should allow for any electrical interference likely to exist. It should allow for input signal scanning rates compatible with the behaviour of the plant. The computers and storage systems should have access times appropriate to the functions to be performed.
The planning of the computer system should consider its location, operating environment and electrical supplies. The staffing for operation and for maintenance, the availability of spare modules, and the repair of faults should he considered.
Where printout equipment is used, it should be suitably sound-proofed or placed in a separate room or enclosure.
7.3 System state indication
The plant operators should have direct indication of the operational condition of the computer system. Alarms should be provided on major failure of the computer and the computer itself should provide alarm information on failure within the computer system units. The computer record of time and date should be available for output.
7.4 Operator control of computer functions The plant operators should have simple direct controls over the computer on-line operation. Push button controls, keyboards and numerical code selection may be used.
An acknowledgement signal should be provided by the computer within 1 s when the operators request a function. A signal should be provided when a function is complete.
Where monitoring, control or equipment protection functions are involved, alterations of settings and controls for operation or for equipment protection system use shall have locks or appropriate administrative control over their use.
7.5 Display control
Direct push button or switch actions close to display units should be used to control alarm and data displays. Touchwire, light pen and other interactive methods may be appropriate. An index of displays should be available to the operator.
13 Equipment protection
Computer systems can be used for equipment protection and interlock purposes. Computers may be suitable for equipment protection especially where large quantities of data complex logic or calculation functions make other methods uneconomic.
Computer protective systems may involve data acquisition, signal evaluation, calculation, logic functions, and initiation of equipment protective action or prevention of incorrect operations.
Before implementation of equipment protection using computers, the criteria for fault detection shall be precisely defined and the system or equipment behaviour and the time from fault occurrence to initiation of corrective action shall be determined.
The computer system application class should be carefully evaluated for equipment protection applications.
A computer system can be used to protect equipment from damage by provision of interlocks, initiation of trips, controlled shut-downs and load reductions. The reliability required for these functions, together with any independent protection equipment provided, determines the application class.
When an equipment protective function is provided only by a computer under specific plant conditions (for example a start-up or change of operating mode), the system should then be designed such that computer failure at that condition initiates the interlock or protective function. Initiation of interlock or protective function on computer failure at other plant operating conditions should be prevented.
An equipment protection application of Class 3 should only have a supplementary function to separate independent protection equipment in order to avoid limiting plant operation during computer system failure.
An equipment protection application of Class 2 necessarily implies redundancy of computer equipment such that the protection remains available in the presence of single computer system failures.