12-10-2012, 04:25 PM
CRITERIA FOR PROGRAMMABLE DIGITAL COMPUTER SYSTEM SOFTWARE IN SAFETY-RELATED SYSTEMS OF NUCLEAR POWER PLANTS
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INTRODUCTION
Criterion 21, "Protection system reliability and testability," of Appendix A, "General Design Criteria for Nuclear Power Plants," in 10 CFR Part 50, "Dorlestic Licensing of Production and Utilization Facilities," requires, among other things, that protection systems be designed for high functional reliability commensurate with the safety function to be performed. Criterion III, "Design Control," of Appendix B, "Quality Assurance Criteria for Nuclear Power Plants and Fuel Reprocessing Plants," of 10 CFR Part 50 requires, among other things, that quality standards be specified and that design control measures be provided for verifying or checking the adequacy of design.
This guide describes a method acceptable to the NRC staff for complying with the Commission's regulations for promoting high functional reliability for safetyrelated systems using programmable digital computer systems in the operation of nuclear power plants. This method is applicable to designing software, verifying software, implementing software, and validating computer systems.
DISCUSSION
Computer technology can provide new capabilities to nuclear power plant protection and control systems. The NRC staff encourages the application of advanced technology such as programmable digital computers in the operation of nuclear power plants if such advanced technology serves to enhance safety.
In 1978, a joint working group consisting of members of the American Nuclear Society (ANS) and of the Institute of Electrical and Electronics Engineers (IEEE) was formed with a charter to develop a joint standard containing general guidance for system design and specific guidance on stage-by-stage testing, overall performance assurance, and documentation of software for programmable digital computer systems in safety-related systems of nuclear power plants. Because of the unique nature of programmable digital computer systems, especially with respect to software, the standard was intended to supplement IEEE Std 603-1980, "Standard Criteria for Safety Systems for Nuclear Power Generating Stations,"' which establishes the functional and design criteria for the power, control, and instrumentation portion of safety-related systems for nuclear power plants. This joint standard was approved by the IEEE Nuclear Power Engineering Committee and the ANS Nuclear Power Plant Standards Committee and has been published as ANSI/IEEE-ANS-7-4.3.2-1982, "Application Criteria for Programmable Digital Computer Systems in Safety Systems of Nuclear Power Generating Stations."
IMPLEMENTATION
The purpose of this section is to provide information to applicants and licensees regarding the NRC staff's plans for using this regulatory guide.
Except in those cases in which an applicant or licensee proposes an acceptable alternative method for complying with specified portions of the Commission's regulations, the method described -in this guide will be used by the staff in its -evaluation of software for all applications in which programmable digital computers are used in safety-related systems of nuclear power plants submitted after November 1985. Licensees and applicants may use this guide as justification of currently pending applications for use of programmable digital computers; however, the staff does not intend to apply this guide to applications currently under review or to operating plants.
BACKGROUND
Value
Compared to current analog methods of processing variables, digital computers are considered to offer advantages in accuracy, reliability, and versatility, even though they are more vulnerable to subtle failure modes and unauthorized manipulation. Merit is seen in their application to safety-related variables and processes.
General guidance for the design of protection system hardware is provided in IEEE Std 603-1980, "Standard Criteria for Safety Systems for Nuclear Power Generating Stations." Heretofore there has been no such guidance for the design of protection system software. However, a joint working group consisting of members of the American Nuclear Society and the Institute of Electrical and Electronics Engineers has developed a standard, ANSI/IEEE-ANS-7-4.3.2-1982, that contains general guidance for system design and specific guidance on stage-by-stage testing, overall performance assurance, and documentation of software for programmable digital computer systems in safety-related systems of nuclear power plants. This action is to endorse the standard developed by the joint working group.