Document: NRC Regulatory Guide
Document ID: 49ce24c8-1a15-48b2-9e26-8c6c2f9064f7
Document Type: regulatory_guide
Title: Dedication of Commercial-Grade Digital I&C Items for Use in Nuclear power Plants
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML2200/ML22003A180.pdf
Revision Date: 2023-05
Chapter: 
Section ID: RG-1.250
CFR Part: 
CFR Title: 

Content:
er, a third type of characteristic, referred to as “dependability,” is identified as being important when dedicating digital equipment that includes software. Dependability characteristics address attributes that are difficult to verify through testing or inspection alone and are heavily influenced by the quality of the processes used to produce the device or software. High-quality software is typically achieved by building quality in, using a systematic life cycle development approach that includes validation and verification steps at each stage of the development life cycle. The degree of dependability of digital devices is also influenced by the incorporation of designed-in elements to provide a robust hardware and software architecture, self-checking features, hardware- or software-based watchdog timers, and controlled failure management, such as use of redundant processors with automatic fail-over capabilities. An evaluation process that incorporates a critical examination of hardware and software development processes, design features (e.g., fault tolerance, diagnostic monitoring coverage, fail-safe design), and historical operating performance is needed to assess the overall dependability of a digital device. TR-106439 refers to this assessment as a critical digital review (CDR). The CDR requires an understanding of the specific programmable logic and hardware features embodied in the design, to verify that they are correct and appropriate considering the requirements of the intended application. Table 4-1 in TR-106439 summarizes a set of attributes associated with dependability critical characteristics for digital equipment. This table provides acceptance criteria, methods of verification, and remarks on the application of those methods of verification. Table 4-2 in TR-106439 identifies examples of design factors that can be evaluated in assessing digital item quality. However, TR-106439 states, “The dedicator must determine which activities are