Document: NUREG-0800
Document ID: 409035a3-eae4-4524-8ae0-ca7775f4072a
Document Type: srp
Title: Revision 5 - March 2007
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0705/ML070550073.pdf
Revision Date: 2023-06
Chapter: 7
Section ID: 7
CFR Part: 
CFR Title: 

Content:
esigned and implemented using a process that conforms with the guidance in SRP BTP 7-14. Software design and implementation for specific applications may be easier to implement for PLCs due to the use of high level languages and the fact that many service functions are already included as part of the commercial product. PLC application software 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 software, provided the experience is commensurate with the reactor application and 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. SRP Appendix 7.0-A, subsection 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 the application. An I&C system built using PLCs contains a number of purchased components: hardware, including the processor, memory, I/O equipment, communications equipment, terminals, etc.; and 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, such as maintenance, verification and validation, electromagnetic interference, and calibration, apply and should be reviewed. The staff should not accept an argument