Document: NUREG-0800
Document ID: 2ceb30a4-38c9-442c-bd66-5a699d0e6480
Document Type: srp
Title: Appendix 7-A
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0525/ML052500554.pdf
Revision Date: 2023-06
Chapter: 7
Section ID: 7
CFR Part: 
CFR Title: 

Content:
o implement for applications produced using the high-level languages typical of PLCs. PLC applications are usually coded using ladder logic or sequential function charts. The resulting programs can be expected to use standard functions provided by the PLC vendor. Standard functions may have considerable industrial experience. This experience may supplement other methods of evaluating the quality of the PLC program, provided that the experience is commensurate with the reactor application, and that field trouble reports are generated, available, and reviewed. If existing industrial experience cannot be shown to be applicable to the safety system application, it is of limited use. Appendix 7.0-A, Section C.3 describes the advantages of using high-level languages such as ladder logic and function charts. It also describes precautions that should be observed when reviewing systems specified or designed using such languages. Many vendors of PLCs allow programming languages other than ladder-logic to be used (e.g., C). The reviewer should take this possibility into account and assess the impact of using programming languages on the design of the PLC and on the application. An I&C system built using PLCs contains a number of purchased components: the hardware, including the processor, memory, I/O equipment, communications equipment, terminals, etc.; and the software, consisting of one or more operating systems, interpreters, compilers, libraries, configuration software, tools, and variations thereof. This purchased equipment should be of a quality appropriate to the proposed application. Other issues associated with the application of digital computers to I&C systems (e.g., maintenance, verification and validation, EMI, and calibration) apply and should be reviewed. The Staff should not accept an argument that the PLC is somehow simpler or different from a computer and hence does not require the rigorous review that a computer system would receive. Appendix 7-A Rev. 4 —