At the time this issue was identified in NUREG-0371,[1] trends in the design of nuclear power plants showed an increase in the use of digital computer technology in safety-related instrumentation and control systems. The first application of this technology was Arkansas Nuclear One, Unit 2 (ANO-2), where digital computers were used in the initiating logic for two reactor trip parameters. After the ANO-2 application, other digital computers, such as core protection calculators, were installed by licensees to provide reactor trip signals.
Since digital technology is considerably different from analog technology, the criteria appropriate for the safety review of digital computer-based systems are different from those used for analog-based systems. Thus,
in this issue, the staff identified the need to standardize the safety review of reactor protection systems that incorporated digital computers. It was believed that the results of such standardization would be: (1) the definition of the staff's requirements for the design, development, and qualification of digital computers for use
by applicants; and (2) an SRP[2] that would define uniform and consistent guidelines for the conduct of the staff's safety review.
In 1982, ANS and IEEE jointly approved the standard ANSI/IEEE-ANS-7-4.3.2[3] which established a method for designing, verifying, and implementing software, and validating computer systems used in the safety-related
systems of nuclear power plants.[4] In 1985, the NRC issued Regulatory Guide 1.152[5] which endorsed
the method in ANSI/IEEE-ANS-7-4.3.2-1982.[6] At the time this issue was evaluated in 1991, the staff was conducting a research program to investigate the use of digital computer safety systems at nuclear power
plants.[7] In particular, specific licensing needs in the area of microcomputer and Artificial Intelligence Systems had been identified and were to be addressed. The desired end product of the research effort was a regulatory guide for the design, development, acceptance testing, and periodic functional verification of Class 1E computer
safety systems, and an SRP[8] addendum providing review guidance for digital computer systems in nuclear power plant safety systems (by referencing Regulatory Guide 1.152[9] and the new regulatory guide).
Since this issue addressed the use of alternative (i.e., digital instead of analog) technology for nuclear power plant safety systems, it was not intended that the use of digital technology would result in a change in the safety of existing nuclear power plants. Thus, the issue addressed the staff's efforts in improving its capability to make independent assessments of safety and was classified as a Licensing Issue.
As a part of the improvements to NUREG-0933, the NRC staff clarified in SECY-11-0101, "Summary of Activities
Related to Generic Issues Program," dated July 26, 2011,[10] that the Generic Issues Program will not pursue any further actions toward resolution of licensing and regulatory impact issues. Because licensing and regulatory impact issues are not safety issues by the classification guidance in the legacy Generic Issues Program, these issues do not meet at least one of the Generic Issues Program screening criteria and do not warrant further processing in accordance with Management Directive 6.4, "Generic Issues Program," dated November 17,
2009.[11] Therefore, this issue will not be pursued any further in the Generic Issues Program.
[1] NUREG-0371, "Task Action Plans for Generic Activities (Category A)," U.S. Nuclear Regulatory Commission, November 1978.
[2] NUREG-0800, "Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants," U.S. Nuclear Regulatory Commission, (1st Ed.) November 1975, (2nd Ed.) March 1980, (3rd Ed.) July 1981.
[3] ANSI/IEEE-ANS-7-4.3.2-1982, "Application Criteria for Programmable Digital Computer Systems in Safety Systems of Nuclear Power Generating Stations," American Nuclear Society, July 6, 1982.
[4] NUREG/CR-5420, "Multiple System Responses ProgramIdentification of Concerns Related to a Number of Specific Regulatory Issues," U.S. Nuclear Regulatory Commission, October 1989.
[5] Regulatory Guide 1.152, "Criteria for Programmable Digital Computer System Software in Safety- Related Systems of Nuclear Power Plants," U.S. Nuclear Regulatory Commission, November 1985. [8511220286]
[6] ANSI/IEEE-ANS-7-4.3.2-1982, "Application Criteria for Programmable Digital Computer Systems in Safety Systems of Nuclear Power Generating Stations," American Nuclear Society, July 6, 1982.
[7] Memorandum for M. Virgilio from S. Newberry, "Proposed Research Programs to Support SICB Regulation Needs," April 26, 1990. [9005090104]
[8] NUREG-0800, "Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants," U.S. Nuclear Regulatory Commission, (1st Ed.) November 1975, (2nd Ed.) March 1980, (3rd Ed.) July 1981.
[9] Regulatory Guide 1.152, "Criteria for Programmable Digital Computer System Software in Safety- Related Systems of Nuclear Power Plants," U.S. Nuclear Regulatory Commission, November 1985. [8511220286]
[10] SECY-11-0101, "Summary of Activities Related to Generic Issues Program," July 26, 2011. [ML111590814]
[11] Management Directive 6.4, "Generic Issues Program," U.S. Nuclear Regulatory Commission, November 17, 2009.
Page Last Reviewed/Updated 06/24/2025