Document: NUREG-0800
Document ID: 96afb1d6-6ce9-41e4-b4ec-1fc7747bc0b2
Document Type: srp
Title: Revision 8 – January 2021
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML2033/ML20339A647.pdf
Revision Date: 2023-05
Chapter: 7
Section ID: 7
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Content:
ensure that reviews apply the appropriate RGs and endorsed industry standards. A. BACKGROUND Digital technology offers significant operational and maintenance benefits for I&C systems of nuclear power plants (NPPs). Digital instrumentation and control (DI&C) systems consist of both hardware components and logic elements (e.g., software). Hardware components in DI&C systems are susceptible to failures similar to those considered for analog systems. In this guidance, the term “software” refers to software, firmware,1 and logic developed from software-based development systems (e.g., hardware description language programmed devices). DI&C systems or components are vulnerable to common-cause failures (CCFs) due to latent design defects in active hardware components, software, or software-based logic.2 A CCF occurs when multiple (usually identical) systems or components fail due to a shared cause.3 Latent design defects are errors in the design of the DI&C system or component that can remain undetected despite rigorous design-basis development, verification, validation, and testing processes. Certain events, unexpected external stresses, or plant conditions can trigger latent design defects within redundant portions (e.g., safety divisions) of a system designed to perform safety functions and thus lead to a systematic failure. CCFs can have two different effects: (1) they can cause a loss of the capability to perform a safety function or can initiate a plant transient, or (2) they can initiate the operation of a function without a valid demand or can cause an erroneous (i.e., spurious) system action. The latter is typically referred to as “spurious operation” or “spurious actuation.” CCFs with a loss of safety function are postulated concurrent with an anticipated operational occurrence (AOO), a postulated accident (PA), or normal operations, while spurious operations are postulated as an initiating event. In accordance with Commission direction in the staff