Document: NUREG-0800
Document ID: 757b676a-0f71-4094-8677-ca3a50743281
Document Type: srp
Title: Revision 7 – August 2016
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1601/ML16019A344.pdf
Revision Date: 2023-06
Chapter: 7
Section ID: 7
CFR Part: 
CFR Title: 

Content:
mmable logic devices, field programmable gate arrays, and application-specific integrated circuits. These digital devices and components use software to develop the logic that later resides within the digital component (called “firmware”) and often cannot be changed in an individual component. These all should be considered in the assessment of diversity. NUREG/CR-6303, Section 3.2, describes six types of diversity and describes how instances of different types of diversity might be combined into an overall case for the sufficiency of the diversity provided. Typically, several types of diversity should exist, some of which should exhibit one or more of the stronger attributes listed in NUREG/CR-6303. Functional diversity and signal diversity are considered to be particularly effective. The following cautions should be noted where applicable: ● The justification for equipment diversity, or for the diversity of related system logic such as a real-time operating system, should extend to the equipment’s components to assure that actual diversity exists. For example, different manufacturers might use the same processor or license the same operating system, thereby incorporating common failure causes. Claims for diversity on the basis of the difference in manufacturer name are insufficient without consideration of the above. With respect to computer software and software-based logic diversity, experience indicates that independence of failure causes may not be achieved in cases where multiple versions of software, for example, are developed using the same set of software, system, and logic development tools. Other considerations, such as technology, functional and signal diversity that lead to different software, system, and logic requirements form a stronger basis for diversity. 3.9 System Testability If a portion or component of a system can be fully tested, then it can be considered not to have a potential for software-based CCF. Fully tested or 100 percent